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We develop a new avenue to creating the optical spectrometer for the Guillermo Haro astrophysical observatory (Mexico), which combines specifically progressed prism spectrometer with modern acousto-optical approach in the frame of a joint instrument. This schematic arrangement includes two principal novelties. First, we exploit recently developed acousto-optical nonlinearity of the two-phonon light scattering in crystals with linear acoustic losses, which admits an additional physical degree of freedom. This effect allows us to use nonlinear acousto-optical effect for linear processing of optical signals in parallel regime within all the visible range. Similar effect is based on the possibility for tuning the frequency of elastic waves and admits the nonlinear apodization improving the dynamic range. Secondly, we are using the cross-disperser technique with acousto-optical processing for the first time to our knowledge. Additionally, the acousto-optical spectrometers can provide almost 100% efficiency in the acousto-optical interaction in the optimized regime. In the case of 4% Mg doped LiNbO 3 crystal the absorption edge can be shifted down to 370 nm for limited intensity of incoming light. The observation window of optical spectrometer in that observatory is ~ 9 cm, so that the theoretical estimations of maximal performances for a low-loss LiNbO3-crystal for this optical aperture at 405 nm give the spectral resolution 0.0523 A, resolving power 77,400, and number of spots 57,500. The illustrative proof-of-principle experiments with available for us 6-cm LiNbO 3 -crystal have been performed and demonstrated the spectral resolution 0.0782 A at 405 nm and resolving power 51,790.

The designed practically prototype of an advanced acousto-optical radio-wave spectrometer is presented in a view of its application to investigating the Milky Way star formation problems. The potential areas for observations of the cold interstellar medium, wherein such a spectrometer can be exploited successfully at different approximations, are: 1) comparison of the Milky Way case with extragalactic ones at scale of the complete galactic disk; 2) global studies of the Galactic spiral arms; and 3) characterization of specific regions like molecular clouds or star clusters. These aspects allow us to suggest that similar instrument will be really useful. The developed prototype of spectrometer is able to realize multi-channel wideband parallel spectrum analysis of very-high-frequency radio-wave signals with an improved resolution power exceeding 103. It includes the 1D-acousto-optic wide-aperture cell as the input device for real-time scale data processing. Here, the current state of developing this acousto-optical spectrometer in frames of the astrophysical instrumentation is briefly discussed, and the data obtained experimentally with a tellurium dioxide crystalline acousto-optical cell are presented. Then, we describe a new technique for more precise spectrum analysis within an algorithm of the collinear wave heterodyning. It implies a two-stage integrated processing, namely, the wave heterodyning of a signal in an acoustically square-law nonlinear medium and then the optical processing in the same solid-state cell. Technical advantage of this approach lies in providing a direct multi-channel parallel processing of ultra-high-frequency radio-wave signals with the resolution power exceeding 104. This algorithm can be realized on a basis of exploiting a large-aperture effective acousto-optical cell, which operates in the Bragg regime and performs the ultra-high-frequency co-directional collinear acoustic wave heterodyning. The general concept and basic conclusions here are confirmed by proof-of-principle experiments with the specially designed cell of a new type based on a lead molybdate crystal.

An advanced conceptual design of a high-bit-rate triple product acousto-optical processor is presented that can be applied in a number of astrophysical problems. We briefly describe the Large Millimeter Telescope as one of the potential observational infrastructures where the acousto-optical spectrometer can be successfully used. A summary on the study of molecular gas in relatively old (age > 10 Myr) disks around main sequence stars is provided. We have identified this as one of the science cases in which the proposed processor can have a big impact. Then we put forward triple product acousto-optical processor is able to realize algorithm of the space-and-time integrating, which is desirable for a wideband spectrum analysis of radio-wave signals with an improved resolution providing the resolution power of about 105 - 106. It includes 1D-acousto-optic cells as the input devices for a 2D-optical data processing. The importance of this algorithm is based on exploiting the chirp Z-transform technique providing a 2D-Fourier transform of the input signals. The system produces the folded spectrum, accumulating advantages of both space and time integrating. Its frequency bandwidth is practically equal to the bandwidth of transducers inherent in acousto-optical cells. Then, similar processor is able to provide really high frequency resolution, which is practically equal to the reciprocal of the CCD-matrix photo-detector integration time. Here, the current state of developing the triple product acousto-optical processor in frames of the astrophysical instrumentation is shortly discussed.

Optical spectrometer of the Guillermo Haro astrophysical observatory (Mexico) realizes investigations in the visible and near-infrared range 350 - 800 nm and exploits mechanically removable traditional static diffraction gratings as dispersive elements. There is a set of the static gratings with slit-densities 150 - 600 lines/mm and optical apertures 9 cm × 9 cm that provide the first order spectral resolution from 0.8 to 3.2 A/pixel, respectively. However, the needed mechanical manipulations, namely, replacing the static diffraction gratings with various resolutions and following recalibration of spectrometer within studying even the same object are practically inconvenient and lead to wasting rather expensive observation time. We suggest exploiting an acousto-optical cell, i.e. the dynamic diffraction grating tunable electronically, as dispersive element in that spectrometer. Involving the acousto-optical technique, which can potentially provide electronic control over the spectral resolution and the range of observations, leads to eliminating the abovementioned demerits and improving the efficiency of analysis.

We develop an advanced approach to the optical spectrometer with acousto-optical dynamic grating for the Guillermo Haro astrophysical observatory (Mexico). The progress consists of two principle novelties. First is the use of the acousto-optical nonlinearity of two-phonon light scattering in crystals with linear acoustic losses. This advanced regime of light scattering exhibits a recently revealed additional degree of freedom, which allows tuning of the frequency of elastic waves and admits the nonlinear apodization improving the dynamic range. The second novelty is the combination of the cross-disperser with acousto-optical processing. A similar pioneering step provides an opportunity to operate over all the visible range in a parallel regime with maximal achievable resolution. The observation window of the optical spectrometer in that observatory is ∼9 cm, so that the theoretical estimations of maximal performances for a low-loss LiNbOsub3/subcrystal for this optical aperture at λ=405 nm give spectral resolution of 0.0523 Å, resolving power of 77,400, and 57,500 spots. The illustrative proof-of-principle experiments with a 6 cm LiNbOsub3/subcrystal have been performed.

We consider the collinear backward light scattering as one of potential physical mechanisms for creating an advanced collinear acousto-optical filter with significantly improved spectral resolution. Within co-directional crystalline collinear acousto-optical filters, the resolution is inversely proportional to the material’s birefringence, which is ~0.1 in the best case of LiNbO3-crystal. For the backward light scattering this parameter is replaced by the twice refractive index, so that the gain achieves > 45 times in LiNbO3-crystal. Thus, one can expect the resolution ~0.002 A instead of the value ~0.1 – 0.2 A recently obtained by us experimentally for co-directional geometry in that crystal. Moreover, the collinear backward light scattering can be implemented in an extended amount of available materials. However, the main limitation for applying the phenomenon is the acoustic attenuation in ultra-high frequency range peculiar to the materials for acousto-optical filters. Linear acoustic attenuation reduces the length of acousto-optical interaction and limits the spectral resolution. At an initial stage, our studies are concentrated on physical aspects of this phenomenon as well as on possibilities of its application to creating the acousto-optical filters of a high resolution. In particular, the frequency band-shapes of the scattered light intensity exhibit a tendency to specific acousto-optical nonlinearity, i.e. to more and more rectangular profile as the acoustic power density grows. Results of this analysis confirm the above-noted estimations for a triplet of trigonal acousto-optical crystals, having possibly lower acoustic attenuation.

We develop a multi-band spectrometer with a few spatially parallel optical arms for the combined processing of their data flow. Such multi-band capability has various applications in astrophysical scenarios at different scales: from objects in the distant universe to planetary atmospheres in the Solar system. Each optical arm exhibits original performances to provide parallel multi-band observations with different scales simultaneously. Similar possibility is based on designing each optical arm individually via exploiting different materials for acousto-optical cells operating within various regimes, frequency ranges and light wavelengths from independent light sources. Individual beam shapers provide both the needed incident light polarization and the required apodization to increase the dynamic range of a system. After parallel acousto-optical processing, data flows are united by the joint CCD matrix on the stage of the combined electronic data processing. At the moment, the prototype combines still three bands, i.e. includes three spatial optical arms. The first low-frequency arm operates at the central frequencies ~60-80 MHz with frequency bandwidth ~40 MHz. The second arm is oriented to middle-frequencies ~350-500 MHz with frequency bandwidth ~200-300 MHz. The third arm is intended for ultra-high-frequency radio-wave signals about 1.0-1.5 GHz with frequency bandwidth

Regime of effective non-collinear acousto-optical interaction with tangential phase matching had been identified and previously observed only in two limiting cases: in tellurium dioxide (TeO 2 ) at low acoustic frequencies (~60 MHz) and in rutile (TiO 2 ) at ultra-high frequencies (~5 GHz). Both these limits are motivated by optical properties of the chosen materials. Low frequencies in TeO 2 admit designing a wide-aperture acousto-optical cell, but limit the frequency bandwidth. While an acousto-optical cell made of TiO 2 has very small aperture and exhibits low spectral resolution due to the effect of linear acoustic attenuation. Instead of those limits, we propose an advanced regime of the anomalous acousto-optical interaction with tangential phase matching, which allows us varying the frequency range and optimizing all the performances (for instance, the spectral resolution) of a wide-aperture acousto-optical cell made of the chosen crystal, as the case requires. Recently, we had suggested and successfully tested experimentally the revealed additional degree of freedom, i.e. the action of the tilt angle within the refractive indices ellipsoids to manipulate by the performances of crystalline acousto-optical cells. Now, we consider an opportunity of refining this additional degree of freedom within those ellipsoids of crystalline acousto-optical cell through some declination of the acoustic beam. For our investigations, the lithium niobate (LiNbO 3 ) and rutile (TiO 2 ) crystals of about 5 cm length, operating with the slow-shear acoustic mode along the acoustic axes had been selected. The needed theoretical analysis, numerical estimations, and 3D-vector diagrams have been developed to reveal potential benefits of the proposed technique.

Performances of any system for data processing based on acousto-optical technique are mainly determined by parameters of the acousto-optical cell (AOC) exploited within the schematic arrangement. Here, basic properties of the AOC, involved into a novel processor for precise optical spectrum analysis dedicated to modern astrophysical applications, are considered. Because potential applications of this processor will be focused on investigations in extra-galactic astronomy as well as studies of extra-solar planets, an advanced regime of the non-collinear two-phonon light scattering has been elaborated for spectrum analysis with significantly improved spectral resolution. Under similar uprated requirements, the AOC, based on that specific regime in the calomel (Hg 2 Cl 2 ) crystal, had been chosen, and its parameters were analyzed theoretically and verified experimentally. Then, the adequate approach to estimating the frequency/spectral bandwidth and spectral resolution had been developed. The bandwidth was calculated and experimentally realized with the additionally involved tilt angle of light incidence, allowing variations for acoustic frequencies. The resolution was characterized taking into account its doubling peculiar to the nonlinear two-phonon mechanism of light scattering. Proof-of-principle experiments were performed with the calomel AOC of 52 mm optical aperture, providing ~94% efficiency in the transmitted light due to the slow-shear acoustic mode of finite amplitude (the acoustic power density ~150 mW/mm 2 ) with the velocity of 0.347×105 cm/s at the radio-wave acoustic frequency ~71 MHz. As a result, we have obtained the spectral resolution

The specific approach to characterizing the train-average parameters of low-power picosecond optical pulses with the frequency chirp, arranged in high-repetition-frequency trains, in both time and frequency domains is elaborated for the important case when the semiconductor laser is matched by an external single-mode fiber cavity and operates in the active mode-locking regime. This approach involves the joint Wigner time–frequency distributions, which can be created for those pulses due to exploitation of a novel interferometric technique. Practically, the InGaAsP/InP-heterolaser generating at the wavelength 1320 nm was used during the experiments carried out and an opportunity of reconstructing the corresponding joint Wigner time–frequency distributions was successfully demonstrated.

This article is devoted to the problem of improving the frequency resolution inherent in a parallel acousto-optical spectrum analysis via involving an additional nonlinear phenomenon into the data processing. In so doing, we examine possible application of the wave heterodyning to the real-time scale acousto-optical analysis of the frequency spectrum belonging to ultra-high-frequency radio-wave signals peculiar, for example, for radio-astronomy. The nonlinear process of wave heterodyning is realized through providing a co-directional collinear interaction of the longitudinal acoustic waves of finite amplitudes. This process, which is beforehand studied theoretically and investigated experimentally via the acousto-optical technique as well, allows us either to improve the frequency resolution of spectrum analysis at a given frequency range or to increase by a few times the current frequencies of radio-wave signals under processing. The first step along this way is connected with the experimental modeling of the acoustic wave heterodyning in solids via exploitation of the specific acousto-optical cell based on a liquid, which allows the simplest realization of a cell with the needed properties. Then, these theoretical and practical findings are used in our experimental studies aimed at creating a new type of acousto-optical cells, which are able to improve the resolution inherent in acousto-optical spectrum analyzer operating over ultra-high-frequency radio-wave signals. In particular, the possibility of upgrading the frequency resolution through the acoustic wave heterodyning is experimentally demonstrated using the cell made of lead molybdate crystal. The obtained results demonstrate practical efficiency of the novel approach presented.

A new technique of ultrafast analogue-to-digital (A-D) conversion for an all-optical data processing is proposed. This technique is based on the Kerr nonlinearity-induced cross-phase modulation in single-mode Mach–Zehnder interferometer configurations arranged in a specific way. Two schemes, capable of realizing both sequential and parallel A-D conversions of optical signals are considered. The potential for an extremely high-bit-rate processing, up to 1 THz in each converter, is due to a femtosecond time response of Kerr effect in fused silica glass. Optical schemes of proposed devices are presented and algorithmically estimated; their functional capabilities are discussed.

We consider physical conditions for realizing the Bragg regime of one-, two-, and three-phonon scattering of light in optically anisotropic crystalline materials. The exact and closed analytical models for describing these regimes are developed and solved. The performed analysis takes into account an opportunity of realizing 100% efficiency of light scattering in these regimes. Possible applications lie in the fields of creating large-aperture modulators of light. In connection with this, the problems of optimizing the frequency bandwidths and potential resolution of such modulators are studied. Reasonable attention is paid to the contribution of acoustic anisotropy to frequency bandwidth. The analytical results are illustrated by computer simulations and compared with proof-of-principle experimental data related to a multi-phonon light scattering in a tellurium dioxide crystal.

Our work is devoted to the collinear acousto-optical filter governed by the acoustic waves of finite amplitude. It represents a novel bulk-optical component, namely, the dispersive element for optical spectroscopy. This filter is based on specifically doped lithium niobate single crystal that unexpectedly works in the near ultraviolet range as well as this material usually works in the visible range. We examine the phenomena affecting the filter transmission efficiency and its resolution, i.e. the light-induced absorption and photorefraction. A new nonlinear approach is used to characterize performances of this collinear LiNbO3 acousto-optical filter exploiting our revealed specific acousto-optical nonlinearity. We have carried out the experiments with the collinear filter based on the congruent LiNbO3 crystal of 6.3 cm length at λ = 405 and 440 nm to verify our analysis and estimations. We also explore an opportunity to trade an amount of the efficiency to improve the spectral resolution. The transmission efficiency steeply increases with increasing light wavelength and with decreasing length of the filter, nevertheless the efficiency still remains higher than 30% in the near ultraviolet, if the spectral resolution is limited by δλ = 0.28–0.29 A. Moreover, we demonstrate the possibility to reach a resolution as high as δλ = 0.12–0.15 A (R > 24600), preserving at the same time an efficiency higher than 10% over the spectral interval that we considered. It looks like our filter holds the best to our knowledge experimentally confirmed spectral resolution for any collinear acousto-optical spectrometers dedicated to space/airborne operations.

Picosecond optical guiding-center solitons of the first order, peculiar for the cubic Ginzburg–Landau systems, are considered as the sync-signal carriers, being attractive for the transmission through optical fiber network. At first, we analyze the model, governed by the complex cubic Ginzburg–Landau equation in a reduced form, and present an approximate analytical description for the evolution of the main parameters inherent in guiding-center solitons. Then, these soliton-like pulses are compared with fundamental solitons adiabatically perturbed by low losses in optical fiber, being also potentially suitable to be the sync-signal carriers. This comparison suggests a conclusion that guiding-center solitons have considerable advantages in applying as lock-on signals from the viewpoints of energy consumption and ease of implementation. Interferometric technique of measuring time intervals with the help of train-average field strength correlation functions to a sub-picosecond accuracy is developed in the event of arriving the optical soliton-like pulses at a high repetition rate. Such an advantage of this technique as the ability of operating on the trains of low-power picosecond optical pulses, in particular, guiding-center solitons in single-mode fibers is revealed. Results of trial experiments with the mock-up, implemented as optical part of the sync-network for a short base radio-interferometer, are presented.

Both theoretical and experimental studies of an advanced opto-electronic processor realizing the algorithm of digital multiplication via analogue convolution and based on collinear interaction between a pair of the co- or counter-propagating non-optical waves in a crystal are presented. To carry out trial experiments, an acousto-optical realization is chosen for such a processor that exploits both acoustic and acousto-optic nonlinearities. The regime of wave digital multiplication of multi-bit binary data streams using the intermediate mixed binary format is analyzed and tested experimentally. The specific method of digitization for the mixed binary format signals applying the optical components of multi-pulse non-collinear three-wave coupled acousto-optical states is estimated algorithmically and examined experimentally.

Temporal Bragg solitons in the form of three-wave acousto-optical weakly coupled states are studied theoretically and experimentally for the digital amplitude modulation of light. Multi-bit weakly coupled states based conversion of the 1B/1B binary encoded input electronic signals into optical pulse trains in 1B/NB codes is experimentally demonstrated. Then this effect is used for controlling binary encoded optical pulse trains through performing the AND logic operation over multi-bit binary words.

We present an original approach to precise optical spectrum analysis based on combining the nonlinear acousto-optical processing with the cross-disperser technique. This novelty gives us a possibility to overlap all the visible range by the parallel analysis with a gained spectral resolution. For this goal, an advanced rutile-made acousto-optical cell has been designed and tested as dynamic acoustic grating at ultrahigh-frequency to provide the needed slit density to increase the resolving power and the nonlinear apodization to improve the profile of a resolvable spot. Theoretical estimations were developed for low-loss 6-cm rutile-crystal at λ=440 nm, and they show that one can expect the spectral resolution 0.0609 Å, resolving power 72,250, and the number of resolvable spots ∼39,200. The illustrative proof-of-principle experiments with that rutile-crystal-made acousto-optical cell have been carried out. Experimentally we have obtained the spectral resolution ∼0.0815 Å and resolving power ∼54,000.

This investigation represents a deep and advanced analysis of exploiting lithium niobate (LiNbO3) crystals for the collinear acousto-optical tunable filter (AOTF) in violet and near ultraviolet ranges. The selection of this material is motivated by its high birefringence, which is a key parameter for improving the resolution of AOTF. For this matter, we take into account all the important factors that can deteriorate the resolution in order to find extreme conditions for the best performances. In concrete, we analyze the well- known photorefraction effect accompanied by the light induced absorption in those ranges for the LiNbO3 crystals doped by selected materials. The best observed results have been obtained with magnesium (Mg) dopant in the congruent melt of LiNbO3, which also shifts the absorption edge far into the middle UV-range. This analysis had made it possible to formulate the physical criterion determining the enlarged practical limitations of the incident light power density. Together with previously studied non-uniformity and dispersion of the birefringence along the length of acousto-optical interaction in a crystal, we exploit the recently discovered and experimentally confirmed acousto-optical nonlinearity, which can improve the transmission function inherent in the collinear interaction via applying the acoustic waves of finite amplitude in the AOTF. As a result, the obtained spectral resolution is the best available for any collinear AOTF to our knowledge.

We investigate the components of dissipative multi-wave solitons in the form of three-wave weakly coupled states originating within the collinear acousto-optical interaction due to acoustic waves of finite amplitude. This investigation is carried out in a square-law nonlinear birefringent medium with linear optical losses, theoretically and experimentally. Theoretically, we study the three-wave collinear acousto-optical interaction using several acoustic pulse profiles, with the cases of infinite support (when the acoustic pulse envelope is gradually vanishing on the boundaries) and compact support (when acoustic pulse envelope is cut down on the boundaries), and consider the appropriate boundary conditions in a quasi-stationary regime with the phase mismatch. As a theoretical result, one has found that the system can be described; in particular, by the cnoidal Jacobi elliptic functions whose limiting cases lead to hyperbolic and trigonometric solutions. The experiments dedicated to examine these theoretical results have been done with a X-ray irradiated α-quartz crystalline cell enabling the collinear acousto-optical interaction. The cell used the pure longitudinal acoustic wave with the frequency mismatch along the 6 cm interaction length. Two types of acoustic pulses had been generated, namely, hyperbolic-secant pulse (infinite support) and a bounded rectangular pulse (compact support). During these experiments one had observed the optical components peculiar to the mismatched weakly coupled states. Rather well agreement between the theoretical model, simulated numerically, and the obtained data of measurements for the frequency detuning, acoustic power density, and efficiency of the coupled states localization have been achieved.

During subsequent development of the recently proposed multi-frequency parallel spectrometer for precise spectrum analysis of wideband radio-wave signals, we study potentials of new acousto-optical cells exploiting selected crystalline materials at the limits of their capabilities. Characterizing these wide-aperture cells is non-trivial due to new features inherent in the chosen regime of an advanced non-collinear one-phonon anomalous light scattering by elastic waves with significantly elevated acoustic losses. These features can be observed simpler in uniaxial, tetragonal, and trigonal crystals possessing linear acoustic attenuation. We demonstrate that formerly studied additional degree of freedom, revealed initially for multi-phonon regimes of acousto-optical interaction, can be identified within the one-phonon geometry as well and exploited for designing new cells. We clarify the role of varying the central acoustic frequency and acoustic attenuation using the identified degree of freedom. Therewith, we are strongly restricted by a linear regime of acousto-optical interaction to avoid the origin of multi-phonon processes within carrying out a multi-frequency parallel spectrum analysis of radio-wave signals. Proof-of-principle experiments confirm the developed approaches and illustrate their applicability to innovative technique for an advanced spectrum analysis of wideband radio-wave signals with the improved resolution in an extended frequency range.

We present a principally new acousto-optical cell providing an advanced wideband spectrum analysis of ultra-high frequency radio-wave signals. For the first time, we apply a recently developed approach with the tilt angle to a one-phonon non-collinear anomalous light scattering. In contrast to earlier cases, now one can exploit a regime with the fixed optical wavelength for processing a great number of acoustic frequencies simultaneously in the linear regime. The chosen rutile-crystal combines a moderate acoustic velocity with low acoustic attenuation and allows us wide-band data processing within GHz-frequency acoustic waves. We have created and experimentally tested a 6-cm aperture rutile-made acousto-optical cell providing the central frequency 2.0 GHz, frequency bandwidth ∼0.52 GHz with the frequency resolution about 68.3 kHz, and ∼7620 resolvable spots. A similar cell permits designing an advanced ultra-high-frequency arm within a recently developed multi-band radio-wave acousto-optical spectrometer for astrophysical studies. This spectrometer is intended to operate with a few parallel optical arms for processing the multi-frequency data flows within astrophysical observations. Keeping all the instrument's advantages of the previous schematic arrangement, now one can create the highest-frequency arm using the developed rutile-based acousto-optical cell. It permits optimizing the performances inherent in that arm via regulation of both the central frequency and the frequency bandwidth for spectrum analysis.

The Guillermo Haro astrophysical observatory (Mexico) realizes investigations in the visible and near-infrared range . Actually, the classical grating spectrometer with mechanically removable optical filters and diffraction gratings is exploited there. Unfortunately, the regular process of changing the diffraction gratings with different resolutions and recalibrating the spectrometer is inconvenient and wastes expensive time for observations. This is why exploiting an acousto-optical cell as a dynamic dispersive element is practically desirable, because potentially it realizes tuning the spectral resolution and the range of observation electronically and excludes filters. Some aspects of inserting just one dynamic acousto-optical diffraction grating instead of a set of the traditional static diffraction gratings are preliminarily considered.

The unexpected features of square-law nonlinearity inherent in the noncollinear three-phonon acousto-optical interaction controlled by elastic waves of finite amplitude in birefringent crystals with linear acoustic attenuation are distinguished and investigated. They lead to breakthrough applications of strongly nonlinear three-phonon interaction to linear optical spectrum analysis with ∼100% efficiency and qualitatively improved resolution. A principally new physical degree of freedom, unique for this nonlinear phenomenon, is revealed and characterized. The indispensable theoretical developments and proof-of-principle acousto-optical experiments with specially designed wide-aperture tellurium dioxide cells are presented. The obtained experimental results confirm the elaborated approaches, promising potentially the highest possible spectral resolution that one can expect in principle from the acousto-optical technique within optical spectrum analysis.

New physical details inherent in the non-collinear two-phonon Bragg light scattering controlled by ultrahigh frequency elastic waves of finite amplitude are studied in wide-aperture crystals exhibiting moderate linear acoustic losses. Recently, it had been demonstrated that the Bragg regime of light scattering exhibits the specific acousto-optical non-linearity with a set of unit-level maxima. Now, additionally to our previous analysis, we present an advanced analytical description of this phenomenon in the amplitude and frequency domains, and what is more, we orient it mainly at the second unit-level maximum. This non-linearity, together with the linear acoustic losses in an acousto-optical cell, produces a new effect of non-linear apodization. The light beam leaving the cell can suppress the side lobes and grow the dynamic range within the potential optical spectrum analysis. After that, we characterize comprehensively an acousto-optical cell, made of calomel and working within the second maximum of two-phonon light scattering, as a dispersive optical component. Finally, the results of our proof-of-principle experiments with the calomel-made cell operating in the chosen regime are presented and discussed.

We study the potentials of a wide-aperture crystalline calomel-made acousto-optical cell. Characterizing this cell is nontrivial due to the chosen regime based on an advanced noncollinear two-phonon light scattering. Recently revealed important features of this phenomenon are essentially exploited in the cell and are investigated in more detail. These features can be observed more easily and simply in tetragonal crystals, e.g., calomel, exhibiting specific acousto-optical nonlinearity caused by the acoustic waves of finite amplitude. This parametric nonlinearity manifests itself at low acoustic powers in calomel possessing linear acoustic attenuation. The formerly identified additional degree of freedom, unique to this regime, is exploited for designing the cell with an eye to doubling the resolution due to two-phonon processes. We clarify the role of varying the central acoustic frequency and acoustic attenuation using that degree of freedom. Then the efficiency of calomel is exploited to expand the cell’s bandwidth with a cost of its efficiency. Proof-of-principle experiments confirm the developed approaches and illustrate their applicability to innovative techniques of optical spectrum analysis with the improved resolution. The achieved spectral resolution of 0.205 A at 405 nm and the resolving power 19,800 are the best for acousto-optical spectrometers dedicated to space or airborne operations to date as far as we know.

Basic performances of the acousto-optical cells, which can be potentially involved into creating a novel triple-product acousto-optical processor for modern astrophysical applications, are under estimation. The main attention is paid to the time-bandwidth product, because just this parameter can be taken as the most general one for the characterization of performance data inherent in each individual cell. Functional capabilities peculiar to the cells operating over either normal or anomalous light scattering regime are under consideration. Evidently, the anomalous regime of light scattering promises better results. Both the theoretical estimations and the experimental data obtained for a large-aperture acousto-optical cell based on a tellurium dioxide crystal, exploiting the anomalous light scattering, gives the time-bandwidth product equal to about 4000 .

It is well known that an appropriate apodization of the light beam within acousto-optical data processing makes it possible to increase the potential dynamic range of a system up to 40 dB and more. Customary, the Gaussian apodization is used when a light beam incidents on a rectangular uniform operative aperture of acousto-optical cell. However, modern acousto-optics exploits often rather high-frequency radio-wave signals in a view of increasing the frequency bandwidth by itself or/and growing the time-bandwidth product inherent in a cell. Anyway, similar acoustooptical cells operate with such frequencies that acoustic losses become already pronounced, so that the effect of these losses along an aperture of a cell has to be taken into account. Typically, acceptable level of the acoustic losses accounts about 3 − 6 dB per cell’s aperture. By this it means that the expected no-uniformity of distributing the acoustic energy is now not negligible. To obtain really optimized profile of the incident light beam apodization the expected influence of acoustic losses ought to be analyzed and estimated. In connection with aforementioned no-uniformity or asymmetry, one can propose exploiting a quasi-Gaussian profile of the incident light beam reasonably shifted relative to the center of an aperture of the acousto-optical cell with appreciable acoustic losses.

Here we examine a new application of the adaptive detectors based on non-steady-state photo-electro-motive force effect for the detection of higher order correlation functions, aiming the estimation of the parameters of ultra short optical pulses arranged in high-repetition trains. For this purpose three beam interferometer scheme with two signal beams modulated at different frequencies is proposed. Theoretical analysis of non-steady-state photo-EMF current generated by light distribution formed by superposition of three waves is performed and the possibility to detect simultaneously second and higher order correlation function is demonstrated. Potential advantages and disadvantages of such detection scheme for measuring the higher order auto-correlations functions are discussed.

Rather specific types of light diffraction in the condensed matters are analyzed theoretically, so that in fact a set of processes conditioned by a multi-phonon light scattering in the Bragg regime is under investigation. Besides of their scientific novelty, studying these phenomena promises real progress in applications, because practical exploiting of the m - phonon processes in frontier schemes for the acousto-optical spectrum analysis of both optical and radio-signals leads potentially to improving the frequency and/or spectral resolution of the corresponding analyzers by almost m - times. With this in mind, the wave-based description, the corpuscular approach as well as the quantum interpretation of acousto-optical interaction are used here to characterize various aspects related to improving the expected resolution of acousto-optical devices exploiting a multi-phonon light scattering. In so doing, the quantity of orders under consideration is limited by number N ≤ 4 , which is still hopefully possible to be achieved experimentally in Bragg regime. Additionally, a brief description of a multi-order light scattering by usual thin diffraction grating is presented in the appendix for the convenience of its physical comparison with the results obtained for acousto-optics.

Both a high level of developing the spatially spot-like and one-dimensional input devices and the flexibility of a design inherent in two-dimensional optical systems with similar modulating components make it possible to realize various high-bit-rate opto-electronic processors. This is why a one-dimension acousto-optic technique has been involved in data processing and its modeling based on the algorithm of triple product correlations. Practically, triple product correlations originate within an optical scheme including the modulated light source, representing the first input port, and two wideaperture acousto-optical cells forming two other input ports. Due to specifically constructed lens system, initially modulated light beam is crossing sequentially the apertures of acousto-optical cells oriented at right angle to each other. Finally, a CCD-matrix integrates the received optical signal with respect to time and registers the resulting triple product correlations. In a view of arranging similar acousto-optical processor for modeling triple product correlations, we characterize a novel version of the acousto-optical cells exploiting now tellurium-dioxide crystals. Together with this, potential performances of the progressed design for similar processor are estimated as well.

The Fourier transform optical systems, creating an image and/or realizing its accurate spectral characterization, suffer from appearing remarkable level of side-lobes in the image intensity distribution that reduce performances, in particular, the dynamic range of these systems. Therefore, suppressing side-lobes in the image plane represents an actual practical task being important for various scientific and technical applications such as, for example, direct imaging and spectral characterization of Earth-like extra-solar planets or spectrum analysis of ultra-high frequency radio-wave signals with exploiting an advanced acousto-optical technique. We suggest applying as apodization systems novel refractive optical beam shapers of the field mapping type, which are able to convert the input (more or less) uniform intensity distribution, peculiar to the majority of usually exploited sources of light, to arbitrary pre-scripted intensity distributions. In the case of choosing, for instance, Gaussian, cosine on a pedestal, etc. distributions, these shapers make it possible to minimize the total level of side-lobes significantly and to increase, in doing so, the dynamic range of optical data processing up to 40 dB or more. The operation principle of these beam shapers is based on inducing, in a control manner, spherical aberration in order to provide the required intensity profile transformation and further compensation of that aberration. As a result, the beam shapers operate as telescopes of special type; they produce a low divergence collimated beam with a target intensity distribution and flat wave front. We describe the beam shaper design, implementation examples, and results of practical applications to the acousto-optical technique of precise multi-channel spectrum analysis.

We study, theoretically and experimentally, a new type of a multi-phonon Bragg light scattering in an optically anisotropic medium. A four-phonon Bragg anomalous light scattering in a tellurium dioxide crystal was observed using a light-blue optical beam of about 1 W in power from an argon gas-laser. Just the Bragg regime of light scattering was assured experimentally and a pentet of the light orders was distinguished and investigated.

A few optically matched by each other sub-systems related to an advanced prototype of acousto-optical spectrometer for radio-astronomy are analyzed jointly. Rather precise control over the incident light polarization should be assured in the scheme together with a required expanding of the incident light beam. Moreover, the needed light-beam apodization, suppressing side lobes within registration of each individual resolvable spot and increasing the dynamic range of spectrometer, has to be taken into account as well. The current stage of analysis related to afore-mentioned problems as well as the results of trial experiments are presented.

Practical applications to both ground-based and satellite exploitations have demonstrated that acousto-optical spectrum analyzers of radio-signals represent really reliable signal-processing technique for the millimeter radio-astronomy. These spectrometers provide sufficiently high efficiency of operation together with the frequency resolution needed for astronomic observations. The basic component of similar spectrometer is the acousto-optical cell, whose operation is based on its ability to shape large amount of independent dynamic diffractive gratings. Each of them reproduces the amplitude, frequency, and phase of only one spectral component from the signal under analysis. A multi-pixel CCD linear array detects the obtained responses in Fourier plane of the integrating lens. The main peculiarity of this prototype lies in exploiting a large-aperture tellurium-dioxide crystalline acousto-optical cell, oriented almost along the [001]- and [110]-axes. This cell allows a two-phonon light scattering providing the improved frequency resolution in comparison with conventional one-phonon regime. This fact determines technical requirements to the framing sub-systems and performances of the prototype as a whole. Due to rather high anisotropy of tellurium dioxide, the efficiency of both one- and two-phonon light scattering depends essentially on the ellipticity of the incident light polarization, so that high-efficient operation needs the eigen-state elliptic polarization, which is determined by the incidence angle, light wavelength, and accuracy of the cell's crystallographic orientation. Currently, an advanced prototype has used a green laser beam at 532 nm with central acoustic frequency about 52 MHz. The first trial experiments in a two-phonon light scattering regime have shown frequency resolution of about 30 KHz.

Some practical aspects of creating an acousto-optical processor oriented to the calculation of triple auto- and cross-correlations of low-power short optical pulses in time domain are under preliminary consideration. In so doing, the shapes of both the triple auto-correlations and the bispectra inherent in the most commonly used pulses are mathematically expressed and numerically illustrated, and the needed general schematic arrangement for a triple correlation acousto-optical processor is designed and briefly discussed. Then, in a view of exploiting the one-channel wide-aperture acousto-optical cells within operating similar processor, the performances of lead-molybdate crystalline cells are tentatively estimated.

We consider rather specific type of a multi-phonon light scattering in both isotropic and anisotropic media. The analysis performed shows that under some conditions it may be possible to expect realizing various multi-phonon processes of light scattering in a regime, which is very close to practically used Bragg scattering case. Preliminary experiment on a four-phonon Bragg anomalous light scattering has been realized in a tellurium dioxide crystal.

Practical applications confirm that acousto-optical spectrometers of optical and radio signals provide efficient and accurate processing of data in real time scale. The key component of similar spectrometers is an acousto-optical cell, which dictates performances of the optical scheme arrangement. Within non-collinear arrangement of spectrometer, the most compact and simplest scheme of really wide-aperture light beam expander appears with exploiting an even number of prisms. This arrangement of beam expander does not deflect light beam, provides rather high transmission, and needs less precision for alignment than as a lens telescope requires. We describe a four-prism beam expander providing a 35-time magnification and about 65%-transmission at a distance of 10 cm. Within elliptical polarization, this expander exhibits properties of an amplitude filter being sensitive to the angle of beam incidence. In a view of obtaining the needed eigen-states of elliptical polarization at the output of expander, the detailed analysis of polarization features is performed, numerically estimated, and selectively compared with experimental data.

In 1970 - 80s, novel optical spectral devices, electronically tunable acousto-optical filters (AOFs) had been proposed and developed. During the years gone AOFs have been remarkably progressed, and now they are widely exploited, for instance, in astrophysical observations. Schematically, AOFs can be separated on collinear and non-collinear filters, depending on the relative directions of passing the waves through crystalline cell, as well as on sequential and parallel ones, depending on the algorithm of spectrum analysis. Their features are characterized by the amplitude and spectral parameters. Here, we consider a few estimations of an advanced collinear AOF based on calcium molybdate single-crystal. In principle, this new AOF with a 15-microsecond time-aperture operates over all the visible range exhibiting 60%-efficiency at the electric power 1.0 W. Direct square-law dependence for crystal's length and inverse square-law dependence for its bandwidth on this minimal size make possible optimizing this advanced collinear AOF.

An advanced qualitative characterization of simultaneously existing various low-power trains of ultra-short optical pulses with an internal frequency modulation in a distributed laser system based on semiconductor heterostructure is presented. The scheme represents a hybrid cavity consisting of a single-mode heterolaser operating in the active mode-locking regime and an external long single-mode optical fiber exhibiting square-law dispersion, cubic Kerr nonlinearity, and linear optical losses. In fact, we consider the trains of optical dissipative solitons, which appear within double balance between the second-order dispersion and cubic-law nonlinearity as well as between the active-medium gain and linear optical losses in a hybrid cavity. Moreover, we operate on specially designed modulating signals providing non-conventional composite regimes of simultaneous multi-pulse active mode-locking. As a result, the mode-locking process allows shaping regular trains of picosecond optical pulses excited by multi-pulse independent on each other sequences of periodic modulations. In so doing, we consider the arranged hybrid cavity as a combination of a quasi-linear part responsible for the active mode-locking by itself and a nonlinear part determining the regime of dissipative soliton propagation. Initially, these parts are analyzed individually, and then the primarily obtained data are coordinated with each other. Within this approach, a contribution of the appeared cubically nonlinear Ginzburg-Landau operator is analyzed via exploiting an approximate variational procedure involving the technique of trial functions.

Both ground-based and satellite applications have demonstrated that acousto-optical spectrometers of radio-signals represent really reliable signal-processing technique for sub-millimeter and millimeter radio-astronomy due to these devices exhibit rather well efficiency as well as present sufficiently high frequency resolution in reasonably large frequency bandwidth. The key component of spectrometer is the acousto-optical cell, which dictates the basic parameters of signal processing. Its operation is based on the ability of cell to produce a large amount of independent from one another dynamic acoustic diffractive gratings, so that each of them reproduces the amplitude and frequency of only one spectral component from the incoming radio-signal. A multi-pixel CCD linear array detects and digitizes the obtained responses in the Fourier plane of a large-aperture integrating lens. The main peculiarity of this prototype lies in exploiting a large-aperture tellurium dioxide crystalline acousto-optical cell, which is oriented under a small angle to the [001]- and [110]-axes, in the regime of anomalous light scattering by extremely slow acoustic waves providing the improved frequency resolution. This circumstance determines the majority of technical requirements to the framing sub-systems and performances of prototype as a whole. Due to an extremely high anisotropy of this crystal, the efficiency of light scattering depends essentially on the incident light polarization, so that high-efficient operation needs the eigen-state polarization, which is determined by the incidence angle, light wavelength, and accuracy of the cell's crystallographic orientation. The first trial experiments have shown frequency resolution of about 45 KHz within about 1500 parallel frequency channels in real time scale.

vHere, we consider the possibility of involving the photo-EMF detectors in registration of the parameters peculiar to ultrashort optical pulses, and it is compared whit the recently triple correlator via Direct and Cascade Third Harmonic Generation. Knowledge of triple auto-correlation function, whose Fourier transformation shapes the corresponding bispectrum, makes possible recovering such train-average parameters as, for instance, the pulse width and frequency chirp as well as revealing asymmetry of ultra-short pulse envelope. The main advantage of applying the photo-EMF detectors lies in an opportunity to detect triple correlations directly, without any intermediate frequency conversion with optical nonlinear processes in additional crystals. Then, the theory of three-beam-correlations at photosensitive layer of the photo-EMF detector is developed, so that principal possibility of registering the high-order-correlations is demonstrated. It can be done within schematic arrangement including the three-beam Michelson interferometer, so that the obtained high-order-correlations have non-traditional form and need rather specific algorithm for their further processing. Also, the experimental characterizations are presented for gallium arsenide (GaAs) semiconductor and the poly-fluoren 6-co-triphenyldiamine (PF6-TPD) photo-conductor-polymer, which both exhibit the photo-EMF-effect. They both exhibit high-pass transfer functions that give us high vibration stability. This novel approach provides more reliable analyzing train-average parameters of picosecond pulses due to significantly higher level of the output optical signals under processing.

Dissipative three-wave weakly coupled states, appearing within collinear and non-collinear Bragg light scattering in a two-mode square-law nonlinear medium with the linear optical losses, are uncovered. The conditions for localizing these dissipative coupled sates as well as the spatial-frequency distributions of their optical components are studied theoretically in quasi-stationary regime. Then, a set of estimations related to the realization of similar dissipative three-wave coupled states have been performed within the acousto-optical experiments in the α-quartz crystalline cells providing collinear and non-collinear geometries of interactions. The distinguishing feature of these potential experiments is the fact that the presence of linear optical losses affects both shaping these dissipative weakly coupled states and the technique for detection and identification of their optical components.

We present an advanced approach to describing low-power trains of bright picosecond optical dissipative solitary pulses with an internal frequency modulation in practically important case of exploiting semiconductor heterolaser operating in near-infrared range in the active mode-locking regime. In the chosen schematic arrangement, process of the active mode-locking is caused by a hybrid nonlinear cavity consisting of this heterolaser and an external rather long single-mode optical fiber exhibiting square-law dispersion, cubic Kerr nonlinearity, and small linear optical losses. Our analysis of shaping dissipative solitary pulses includes three principal contributions associated with the modulated gain, total optical losses, as well as with linear and nonlinear phase shifts. In fact, various trains of the non-interacting to one another optical dissipative solitons appear within simultaneous balance between the second-order dispersion and cubic-law Kerr nonlinearity as well as between active medium gain and linear optical losses in a hybrid cavity. Our specific approach makes possible taking the modulating signals providing non-conventional composite regimes of a multi-pulse active mode-locking. Within our model, a contribution of the appearing nonlinear Ginzburg-Landau operator to the parameters of dissipative solitary pulses is described via exploiting an approximate variational procedure involving the technique of trial functions.

We discuss specifically elaborated approach for characterizing the train-average parameters of low-power picosecond optical pulses with the frequency chirp, arranged in high-repetition-frequency trains, in both time and frequency domains. This approach had been previously applied to rather important case of pulse generation when a single-mode semiconductor heterolaser operates in a multi-pulse regime of the active mode-locking with an external single-mode fiber cavity. In fact, the trains of optical dissipative solitary pulses, which appear under a double balance between mutually compensating actions of dispersion and nonlinearity as well as gain and optical losses, are under characterization. However, in the contrast with the previous studies, now we touch an opportunity of describing two chirped optical pulses together. The main reason of involving just a pair of pulses is caused by the simplest opportunity for simulating the properties of just a sequence of pulses rather then an isolated pulse. However, this step leads to a set of specific difficulty inherent generally in applying joint time-frequency distributions to groups of signals and consisting in manifestation of various false signals or artefacts. This is why the joint Chio-Williams time-frequency distribution and the technique of smoothing are under preliminary consideration here.

Spectral responsivity and reflectance of two types of InGaAs/InP photodiodes have been measured. The internal quantum efficiency calculated from them has shown that it is possible to obtain an absolute radiometer within 1100 nm and 1500 nm. Models to interpolate reflectance and internal quantum efficiency are presented in this work. Responsivity is the radiometric characteristic of main interest in the fields where these devices are to be used for optical radiation measurements. As it is well known, the responsivity of a photodiode can be calculated if the spectral reflectance and internal quantum efficiency are known [1]. The measurement and interpolation of spectral reflectance and internal quantum efficiency based on a model of layered structure in the diode are presented in this paper. This allows to use this type of photodiode to measure optical power at any wavelength within their spectral sensitivity range without having to calibrate them at every specific wavelength, what is important because of the wide use of this photodiodes to realize spectroradiometric scales in the near IR range.

Practical feasibility of measuring the train-average parameters of picosecond optical pulses being arranged in highfrequency repetition trains is investigated. For this purpose we consider exploiting the triple auto-correlations, whose Fourier transformations give the bispectrum of a pulse train. The main merit of similar approach consists in the capability of recovering signals and revealing asymmetry of pulse envelopes. The triple auto-correlation can be shaped by a three-beam scanning interferometer with the following one- or two-cascade triple harmonic generation. The efficiencies of these processes depend on the number of cascades and differ in various modern materials. The key features of measuring the train-average parameters of pulses with possible frequency chirp are also discussed.

10 páginas, 5 figuras.-- Comunicacion presentada al Congreso: "Physics and Simulation of Optoelectronic Devices XVIII" celebrado en San Francisco (USA) en Enero del 2010., We discuss specifically elaborated technique for characterizing the train-average parameters of low-power picosecond optical pulses with the frequency chirp, arranged in high-repetition-frequency trains, in both time and frequency domains. This technique is applied to rather important case of pulse generation when a single-mode semiconductor heterolaser operates in a multi-pulse regime of the active mode-locking. In fact, the trains of optical dissipative solitary pulses, which appear under a double balance between mutually compensating actions of dispersion and nonlinearity as well as gain and optical losses, are under characterization. The presented approach involves the joint Wigner time-frequency distributions, which can be found for those picosecond optical dissipative solitary pulses due to the exploitation of a novel interferometric technique. Practically, the semiconductor InGaAsP/InP-heterolaser generating at the wavelength 1320 nm was exploited during the illustrating experiments carried out and the possibility of evaluating the corresponding joint Wigner time-frequency distributions has been obviously demonstrated., This work has been financially supported by the CONACyT, Mexico (project # 61237).

The main features of arranging the polarization control in optical scheme of a 1000-channel acousto-optical spectrometer for the needs of radio-astronomy are analyzed. To realize a high-resolution spectrum analysis rather specific acousto-optical cell has to be exploited. For this cell a tellurium dioxide single-crystal oriented along the [001]- and [110]-axes has been chosen. Due to an extremely high anisotropy of this crystal, the efficiency of light scattering depends essentially on the ellipticity of the incident light polarization and increases when the state of polarization reaches the eigen-state of elliptic polarization, which is determined by the incidence angle, light wavelength, and accuracy of the cell's crystallographic orientation. This is why we analyze some peculiarities of designing the beam-shaping scheme, which includes tunable light polarizers and a multi-prism beam expander and has to provide the needed pre-assigned states of light polarization on the inputting aperture of acousto-optical cell.

Estimating the effective photo-elastic constants peculiar to a set of partial processes inherent in a one-phonon Bragg anomalous light scattering of light in tellurium dioxide crystal is progressed. Really high optic and acoustic anisotropy of this crystal leads to the fact that the efficiency of light scattering is critically conditioned by the ellipticity of the incident light polarization and details in the geometry of acousto-optical interaction. Using a technique of the eigenvectors for elliptical states of light polarization in anisotropic medium, we describe analytically the efficiency of a onephonon Bragg anomalous light scattering in and optimized cell, oriented along the [001] and [110] crystallographic axes with variously polarized incident light modes. Possible interpretation of the results obtained is briefly discussed.