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The paper presents the results of the formation of thermochemical laser induced periodic surface structure on Cr thin films (40–350 nm) that was sputtered on the glass substrate. The different dependence of TLIPSS formation on processing rate in case of thin (40 nm) and thick (350 nm) is observed.

In the course of assessing OPC compact modeling capabilities and future requirements, we chose to investigate the interface between CD-SEM metrology methods and OPC modeling in some detail. Two linked observations motivated our study: 1) OPC modeling is, in principle, agnostic of metrology methods and best practice implementation. 2) Metrology teams across the industry use a wide variety of equipment, hardware settings, and image/data analysis methods to generate the large volumes of CD-SEM measurement data that are required for OPC in advanced technology nodes. Initial analyses led to the conclusion that many independent best practice metrology choices based on systematic study as well as accumulated institutional knowledge and experience can be reasonably made. Furthermore, these choices can result in substantial variations in measurement of otherwise identical model calibration and verification patterns. We will describe several experimental 2D test cases (i.e., metal, via/cut layers) that examine how systematic changes in metrology practice impact both the metrology data itself and the resulting full chip compact model behavior. Assessment of specific methodology choices will include: • CD-SEM hardware configurations and settings: these may range from SEM beam conditions (voltage, current, etc.,) to magnification, to frame integration optimizations that balance signal-to-noise vs. resist damage. • Image and measurement optimization: these may include choice of smoothing filters for noise suppression, threshold settings, etc. • Pattern measurement methodologies: these may include sampling strategies, CD- and contour- based approaches, and various strategies to optimize the measurement of complex 2D shapes. In addition, we will present conceptual frameworks and experimental methods that allow practitioners of OPC metrology to assess impacts of metrology best practice choices on model behavior. Finally, we will also assess requirements posed by node scaling on OPC model accuracy, and evaluate potential consequences for CD-SEM metrology capabilities and practices.

The semiconductor industry is moving toward a half-pitch of 7 nm. The required metrology equipment should be one order of magnitude more accurate than that. Any metrology tool is only as good as it is calibrated. The characterization of metrology systems requires test patterns that are one order of magnitude smaller than the measured features. The test sample was designed in such a way that the distribution of linewidths appears to be random at any location and any magnification. The power spectral density of such pseudo-random test pattern is inherently flat, down to the minimum size of lines. Metrology systems add a cut-off of the spectra at high frequencies; the shape of the cut-off characterizes the system in its entire dynamic range. This method is widely used in optics, and has allowed optical systems to be perfected down to their diffraction limit. There were attempts to use the spectral method to characterize nanometrology systems such as SEMs, but the absence of natural samples with known spatial frequencies was a common problem. Pseudo-random test patterns with linewidths down to 1.5 nm were fabricated. The system characterization includes the imaging of a pseudo-random test sample and image analysis by a developed software to automatically extract the power spectral density and the contrast transfer function of the nanoimaging system.

Monte Carlo-based SEM image simulation can reproduce SEM micrographs by calculating scattering events of primary electrons inside the target materials. By using the simulated SEM images, it is possible to optimize imaging conditions prior to the specimen observation, which could save time for finding suitable observation condition. However, a recent trend of miniaturized and 3-dimentional structures of semiconductor devices, and introduction of various novel materials have created a challenge for such SEM image simulation techniques; that is, more precise and accurate modeling is required. In this paper, we present a quantitatively accurate BSE simulation and a precise parameters setting in voltage contrast simulation, for both to reproduce experimental SEM images accurately. We apply these simulation techniques to optimize the accelerating voltage of SEM for sub-surface imaging, and to analyze a charge distribution on the insulating specimen under the electron irradiation. These applications promise the advancement in developing a new device by preparing inspecting condition in a timely manner.

Femtosecond-pulse modification of the refractive index in transparent materials enables the inscription of fiber Bragg gratings with new features and extended capabilities. In this study we present the results of fiber Bragg gratings inscription in Corning 62.5/125 multimode graded index fiber with IR femtosecond laser pulses. The specifics of point-by-point inscription including single and multiple Bragg grating inscription in limited fiber segment as well as different transverse modes excitation/suppression is discussed. Multimode fiber Bragg gratings inscribed with femtosecond radiation are investigated for the first time directly in the Raman fiber laser cavity.

Experimental investigation of thermochemical laser-induced periodic surface structures (TLIPSS) formation on metal films (Ti, Cr, Ni, NiCr) at different processing conditions is presented. The hypothesis that the TLIPSS formation depends significantly on parabolic rate constant for oxide thin film growth is discussed. Evidently, low value of this parameter for Ni is the reason of TLIPSS absence on Ni and NiCr film with low Cr content. The effect of simultaneous ablative (with period ≈λ) and thermochemical (with period ≈λ) LIPSS formation was observed. The formation of structures after TLIPSS selective etching was demonstrated.

The concept of random lasers exploiting multiple scattering of photons in an amplifying disordered medium in order to generate coherent light without a traditional laser resonator has attracted a great deal of attention in recent years. This research area lies at the interface of the fundamental theory of disordered systems and laser science. The idea was originally proposed in the context of astrophysics in the 1960s by V.S. Letokhov, who studied scattering with “negative absorption” of the interstellar molecular clouds. Research on random lasers has since developed into a mature experimental and theoretical field. A simple design of such lasers would be promising for potential applications. However, in traditional random lasers the properties of the output radiation are typically characterized by complex features in the spatial, spectral and time domains, making them less attractive than standard laser systems in terms of practical applications. Recently, an interesting and novel type of one-dimensional random laser that operates in a conventional telecommunication fibre without any pre-designed resonator mirrors–random distributed feedback fibre laser–was demonstrated. The positive feedback required for laser generation in random fibre lasers is provided by the Rayleigh scattering from the inhomogeneities of the refractive index that are naturally present in silica glass. In the proposed laser concept, the randomly backscattered light is amplified through the Raman effect, providing distributed gain over distances up to 100 km. Although an effective reflection due to the Rayleigh scattering is extremely small (∼0.1%), the lasing threshold may be exceeded when a sufficiently large distributed Raman gain is provided. Such a random distributed feedback fibre laser has a number of interesting and attractive features. The fibre waveguide geometry provides transverse confinement, and effectively one-dimensional random distributed feedback leads to the generation of a stationary near-Gaussian beam with a narrow spectrum. A random distributed feedback fibre laser has efficiency and performance that are comparable to and even exceed those of similar conventional fibre lasers. The key features of the generated radiation of random distributed feedback fibre lasers include: a stationary narrow-band continuous modeless spectrum that is free of mode competition, nonlinear power broadening, and an output beam with a Gaussian profile in the fundamental transverse mode (generated both in single mode and multi-mode fibres). This review presents the current status of research in the field of random fibre lasers and shows their potential and perspectives. We start with an introductory overview of conventional distributed feedback lasers and traditional random lasers to set the stage for discussion of random fibre lasers. We then present a theoretical analysis and experimental studies of various random fibre laser configurations, including widely tunable, multi-wavelength, narrow-band generation, and random fibre lasers operating in different spectral bands in the 1–1.6 μm range. Then we discuss existing and future applications of random fibre lasers, including telecommunication and distributed long reach sensor systems. A theoretical description of random lasers is very challenging and is strongly linked with the theory of disordered systems and kinetic theory. We outline two key models governing the generation of random fibre lasers: the average power balance model and the nonlinear Schrodinger equation based model. Recently invented random distributed feedback fibre lasers represent a new and exciting field of research that brings together such diverse areas of science as laser physics, the theory of disordered systems, fibre optics and nonlinear science. Stable random generation in optical fibre opens up new possibilities for research on wave transport and localization in disordered media. We hope that this review will provide background information for research in various fields and will stimulate cross-disciplinary collaborations on random fibre lasers.

Reflection properties of a fiber Bragg grating (FBG) inscribed in a multimode fiber strongly depend on the transverse profile of FBG. Point-by-point FBG fabrication by IR femtosecond pulses with highly nonlinear refraction index variation as a function of intensity within the focal spot offers an opportunity to tailor the FBG transverse profile with high spatial resolution. In this paper we review our recent results on the femtosecond inscription of FBGs in multimode fibers, study of their spectral and mode-selective properties as well as applications for mode selection in multimode and multicore fiber lasers.

We study Raman lasing in a 7 m polarization-maintaining fiber with an array of fiber Bragg gratings with random phases/amplitudes. After optimization of the grating number the threshold pump power decreases to 0.8 W, whereas generated Stokes power at 1092 nm grows linearly above the threshold, reaching ~3 W for both forward and backward waves. A comparison of experimental data with a developed model shows what such a random laser generates in a coherent regime. Near the threshold, single-longitudinal-mode generation with a ~50 kHz linewidth is obtained, whereas the number of generated modes grows with power exceeding ~100 at ~0.1 W. At higher power, a transition to an incoherent regime with different power increments is observed, while the linewidth grows nonlinearly reaching ~80 pm. Insertion of a 30 m fiber before gratings enables ~1.5 times higher backward Stokes power at a narrower linewidth. Additionally, tunable parametric generation around 1140 nm is observed.

In this paper, we present a new method of point-by-point femtosecond inscription of fiber Bragg gratings (FBG) arrays of different configurations in a 7-core spun optical fiber. The possibility of FBGs inscription with predefined periods in individual fiber cores allowed us to realize: 1) longitudinal FBG arrays with identical or variable resonant wavelengths in all side cores, 2) longitudinal FBG arrays inscribed only in the central or in the selected side core, and 3) an FBG array in a transverse cross section of a fiber consisting of an FBG inscribed in the central and three side cores. Based on the proposed method, by enabling the inscription through the acrylate protective coating of the fiber, a vector bend sensor has been created. Implementation of this sensor has shown that bending radii less than 4 mm can be measured with a high precision using a single-channel interrogation scheme.

In this chapter we briefly review the basic principles of Raman fiber lasers operating via random distributed feedback, including details of feedback mechanism, various cavity designs, and corresponding power and spectral characteristics, as well as their statistical properties. We also compare performances of the random Raman fiber lasers (RRFLs) with that for conventional Raman fiber lasers (RFLs) with linear cavity based on two reflectors. The performance analysis includes polarization management, optimization of conversion efficiency, cascaded generation of higher Stokes orders, opportunities for short-wavelength generation via direct pumping by high-power laser diodes, or frequency doubling of random Raman fiber laser radiation. Pulsed operation of random Raman fiber lasers via active or passive Q-switching is also analyzed. The analysis shows that the output characteristics of Raman fiber lasers with random distributed feedback reached to the moment already outperform in many aspects those for conventional Raman fiber lasers. The unique performance of random fiber lasers opens the door to their application in advanced technologies, such as long-distance amplifier-free transmission and remote sensing, low-coherence IR, and visible sources for bio-imaging and others.

A review of recent results on synchronous generation of Raman dissipative solitons in dissipative-soliton fiber laser cavity, as well as comb of highly-chirped pulses obtained at mixing of Raman and main dissipative solitons, is given.

All-fiber Raman laser based on a graded-index fiber directly-pumped by multimode laser diodes is demonstrated for the first time. High-quality narrowband output of 50 W at 954 nm is generated with slope efficiency of 67%.

The formation of thermochemical laser-induced periodic surface structures (TLIPSS) on 400-nm Ti films deposited onto a glass substrate is investigated under irradiation by a femtosecond laser with a wavelength of 1026 nm, pulse duration of 232 fs, repetition rate of 200 kHz, and with different spot sizes of 4–21 μm. The optimal fluence for TLIPSS formation reduces monotonously with increasing the spot diameter in the range. It is found that the standard deviation of the TLIPSS period depends significantly on the beam size and reaches approximately 2% when the beam diameter is in the range of 10–21 μm. In addition to TLIPSS formation with the main period slightly smaller than the laser wavelength, an effect of TLIPSS spatial frequency doubling is detected. The optical properties of TLIPSS (reflection spectrum and diffraction efficiency at different incident angles and polarizations) are investigated and compared with theoretical ones to give a basis for the development of an optical inspecting method. The refractive index and absorption coefficient of oxidized ridges of the TLIPSS are theoretically estimated by simulation of the experimental reflection spectrum in the zeroth diffraction order.

The main source of placement error in maskmaking using electron beam is charging. DISPLACE software provides a method to correct placement errors for any layout, based on a physical model. The charge of a photomask and multiple discharge mechanisms are simulated to find the charge distribution over the mask. The beam deflection is calculated for each location on the mask, creating data for the placement correction. The software considers the mask layout, EBL system setup, resist, and writing order, as well as other factors such as fogging and proximity effects correction. The output of the software is the data for placement correction. Unknown physical parameters such as fogging can be found from calibration experiments. A test layout on a single calibration mask was used to calibrate physical parameters used in the correction model. The extracted model parameters were used to verify the correction. As an ultimate test for the correction, a sophisticated layout was used for verification that was very different from the calibration mask. The placement correction results were predicted by DISPLACE, and the mask was fabricated and measured. A good correlation of the measured and predicted values of the correction all over the mask with the complex pattern confirmed the high accuracy of the charging placement error correction.

Random fiber lasers operating via the Rayleigh scattering (RS) feedback attract now a great deal of attention as they generate a high-quality unidirectional laser beam with the efficiency and performance comparable and even exceeding those of fiber lasers with conventional cavities. Similar to other random lasers, both amplification and random scattering are distributed here along the laser medium being usually represented by a kilometers-long passive fiber with Raman gain. However, it is hardly possible to utilize normal gain in conventional active fibers as they are usually short and RS is negligible. Here we report on the first demonstration of the RS-based random lasing in an active fiber. This became possible due to the implementation of a new Bi-doped fiber with an increased amplification length and RS coefficient. The realized Bi-fiber random laser generates in a specific spectral region (1.42 μm) exhibiting unique features, in particular, a much narrower linewidth than that in conventional cavity of the same length, in agreement with the developed theory. Lasers of this type have a great potential for applications as Bi-doped fibers with different host compositions enable laser operation in an extremely broad range of wavelengths, 1.15–1.78 μm.

In maskmaking, the main source of error contributing to placement error is charging. DISPLACE software corrects the placement error for any layout, based on a physical model. The charge of a photomask and multiple discharge mechanisms are simulated to find the charge distribution over the mask. The beam deflection is calculated for each location on the mask, creating data for the placement correction. The software considers the mask layout, EBL system setup, resist, and writing order, as well as other factors such as fogging and proximity effects correction. The output of the software is the data for placement correction. One important step is the calibration of physical model. A test layout on a single calibration mask was used for calibration. The extracted model parameters were used to verify the correction. As an ultimate test for the correction, a sophisticated layout was used for the verification that was very different from the calibration mask. The placement correction results were predicted by DISPLACE. A good correlation of the measured and predicted values of the correction confirmed the high accuracy of the charging placement error correction.

We experimentally demonstrate a cascaded generation of a conventional dissipative soliton (DS) at 1020 nm and Raman dissipative solitons (RDS) of the first (1065 nm) and second (1115 nm) orders inside a common fiber laser cavity. The generated high-energy pulses are shown to be linearly-chirped and compressible to 200-300 fs durations for all wavelengths. Moreover, the pulses are mutually coherent that has been confirmed by efficient coherent combining exhibiting ~75 fs and

Random Raman lasers attract now a great deal of attention as they operate in non-active turbid or transparent scattering media. In the last case, single mode fibers with feedback via Rayleigh backscattering generate a high-quality unidirectional laser beam. However, such fiber lasers have rather poor spectral and polarization properties, worsening with increasing power and Stokes order. Here we demonstrate a linearly-polarized cascaded random Raman lasing in a polarization-maintaining fiber. The quantum efficiency of converting the pump (1.05 μm) into the output radiation is almost independent of the Stokes order, amounting to 79%, 83% and 77% for the 1st (1.11 μm), 2nd (1.17 μm) and 3rd (1.23 μm) order, respectively, at the polarization extinction ratio >22 dB for all orders. The laser bandwidth grows with increasing order, but it is almost independent of power in the 1–10 W range, amounting to ~1, ~2 and ~3 nm for orders 1–3, respectively. So, the random Raman laser exhibits no degradation of output characteristics with increasing Stokes order. A theory adequately describing the unique laser features has been developed. Thus, a full picture of the cascaded random Raman lasing in fibers is shown.

We demonstrate a linearly-polarized high efficiency random Raman lasing of the 1st-order Stokes wave and cascaded generation in 0.5- and 1-km-long PM fiber, respectively, under polarized pumping. Quantum efficiency of converting input pump radiation (1.05μm) into the 1st (1.11μm), 2nd (1.17μm) and 3rd-order (1.23μm) Stokes waves is about 80% in the cascaded generation, regardless of the order, and amounts to 92% for the 1st-order Stokes wave in the 0.5-km PM fiber. Polarization extinction ratio is >22 dB for all the waves at output powers of up to 10 W. An analytical model describing adequately the generated power for all components of the cascaded random Raman fiber laser has been developed. The laser bandwidth increases with Stokes order, amounting to ~1, ~2 and ~3 nm for the consecutive orders, respectively.

Digital planar holograms (DPH) are successfully fabricated for the first time by nanoimprint lithography (NIL). A state-of-the-art UV-NIL process is developed by combining both advantages of step and repeat technology at low pressure for high-throughput and imprinting of spin-coated resist films for easy pattern transfer. The nanofabrication process is used in order to replicate DPH structures, composed of multi-million lines grating, into silicon dioxide waveguide core. Optical performances of nanospectrometers chips are in agreement with simulations.

In this paper, we present the study of the thermochemical laser-induced periodic surface structures (TLIPSS) formation on a thin chromium film under femtosecond laser (λ = 1026 nm, τ = 232 fs) irradiation focused on the astigmatic spot with an axis ratio of ≈1/10 and a width along the long side of 155 µm. The effect of the number of laser pulses and the repetition rate (2–200 kHz) on the formation of the structures is investigated. Variation of the number of pulses allowed us to observe the dynamics of the formation of structures. It has been found that the ordering of TLIPSS structures increases with increasing repetition rate of laser pulses, which is explained by the heat accumulation effect on the oxidation process and, consequently, on the formation of TLIPSS structures in the case of a high repetition rate of pulses, which is confirmed by the results of numerical modelling. This effect leads to a different oxidation dynamics and the formation of various types of oxides: predominance of CrO2 in the case of a high-rate impact and an increase in the contribution of Cr2O3 in the case of a low repetition rate of pulses.

Digital planar holography enables the creation of a new generation of integrated photonic circuits with desired transfer function. We give here, for the first time, the basis for designing computer-generated planar holograms and demonstrate their application for spectroscopy-on-chip. Nanospectrometer chips are demonstrated with unmatched spectral resolution of up to 2 ·105. A specific configuration is demonstrated for easy integration of planar holograms into the full spectrometer system. The ultraminiaturization and very high performances of the devices are a breakthrough in spectroscopy and open a novel route for the digital processing of light.

An external-cavity generation of powerful ultrashort pulses in an all-fiber scheme by using a new type of phosphosilicate polarization maintaining fiber is investigated. The phosphorus-related Stokes shifted Raman pulse near 1.3 microns is observed. Optimization of Stokes output spectrum depending on pump pulse duration (chirp), energy and output coupling ratio of the cavity is performed. As result, the output energy of highly-chirped pulses compressible to 570 fs reaches 1.6 nJ.

Nature Communications 6: Article number: 6214 (2015); Published 3 February 2015; Updated 25 May 2018 The original HTML version of this Article had an incorrect volume number of 2; it should have been 6. This has now been corrected in the HTML; the PDF version of the Article was correct from the timeof publication.

A reflectometric approach is proposed for interrogation of multiple fiber Bragg grating (FBG) sensors recorded in a single fiber optic line, based on the differential registration FBGs’ response to a short probing laser pulse using conventional OTDR. A special optical layout has been developed allowing transformation of FBG’s spectrally modulated signals into intensity modulated signals and at the same time eliminating the susceptibility of the system to light power fluctuations. Threshold sensitivity of the method amounted to ~50 μstrain within the measurement range of ~4000 μstrain. The maximum number of FBGs interrogated by the proposed technique is estimated at several hundred, which by far surpasses the requirements of most practical applications. Due to its simplicity, efficiency and usage of conventional OTDR equipment the proposed FBG interrogation technique can find a wide range of applications, in particular in structural health monitoring.

Two types of distributed fiber sensor systems for temperature measurements have been developed: the first one is multi-point Fiber Bragg Grating based system with interrogation by CW tunable laser and nonlinearity compensation by reference interferometer. The second device is Raman scattering system based on optical time domain reflectometry (OTDR) with a pulsed laser providing spatial resolution of several meters and efficient spectral filtering of the Stokes and anti-Sokes signals by means of WDM couplers. Physical effects important for the systems operation are analyzed and their parameters are compared and optimized for applications in oil-gas industry and turbogenerator temperature monitoring.

A distributed feedback (DFB) fiber laser based on a 32-mm long pi-phase-shifted fiber Bragg grating inscribed using the femtosecond point-by-point technique in a single-mode erbium-doped optical fiber (CorActive EDF-L 1500) is demonstrated. The lasing power of the DFB laser reaches 0.7 mW at a wavelength of 1550 nm when pumped with a laser diode at a wavelength of 976 nm and power of 525 mW. The width of the lasing spectrum is 17 kHz. It is shown that the pi-phase-shifted fiber Bragg grating fs-inscribed in a non-PM fiber provides the selection of the single polarization mode of the DFB laser. DFB laser formation in a highly doped non-photosensitive optical fiber (CoreActive SCF-ER60-8/125-12) is also demonstrated.

BEAMETR technique is developed for robust operator independent measurement of electron beam sizes in two coordinates. This method involves software and a specially designed pattern-sample. In this paper, we report the fabrication of this sample and the demonstration of beam size and shape measurements for different Scanning Electron Microscopes and operating conditions (voltage, aperture, astigmatism) with a good consistency. Electron Beam Lithography system (100keV) was used for patterning; proximity correction was applied to improve pattern quality. In this chip version, the minimum feature linewidth was 20nm after lift-off.

© 2015 AIP Publishing LLC. We present a modulation transfer function (MTF) calibration method based on binary pseudo-random (BPR) one-dimensional sequences and two-dimensional arrays as an effective method for spectral characterization in the spatial frequency domain of a broad variety of metrology instrumentation, including interferometric microscopes, scatterometers, phase shifting Fizeau interferometers, scanning and transmission electron microscopes, and at this time, x-ray microscopes. The inherent power spectral density of BPR gratings and arrays, which has a deterministic white-noise-like character, allows a direct determination of the MTF with a uniform sensitivity over the entire spatial frequency range and field of view of an instrument. We demonstrate the MTF calibration and resolution characterization over the full field of a transmission soft x-ray microscope using a BPR multilayer (ML) test sample with 2.8 nm fundamental layer thickness. We show that beyond providing a direct measurement of the microscope's MTF, tests with the BPRML sample can be used to fine tune the instrument's focal distance. Our results confirm the universality of the method that makes it applicable to a large variety of metrology instrumentation with spatial wavelength bandwidths from a few nanometers to hundreds of millimeters.

Raman lasing in a 2.5-km-long multimode graded-index (GRIN) fiber directly pumped by a multimode 915-nm laser diode is studied. Low-index transverse modes at 954 nm are generated with slope efficiency >40%. All-fiber variant is demonstrated. Article not available.

Spatial hole burning in an active medium of a linear cavity Yb-doped fiber laser leads to formation of a dynamical fiber Bragg grating. Reflectivity of the grating (~5%) is measured for the first time.

The all-fiber all-normal-dispersion cavity length and mode-field diameter have been increased simultaneously up to 40-m and 10-μm. By suppressing Raman effect, highly-chirped pulses with energy >50 nJ at 250 fs compressed duration are generated.

Single transverse mode is selected by FBGs inscribed by femtosecond technique in a graded-index fiber. High beam quality and narrow spectrum have been obtained in the Raman fiber laser with multimode 915-nm laser diode pumping.

On the base of the phase shifted fiber Bragg grating of 4 cm length written in the active non-PM Yb-doped fiber, a resonator with distributed feedback (DFB) has been formed. The single frequency single polarization unidirectional generation with the output power up to 4.5 mW has been obtained. The spectral and energy performances of the single frequency DFB fiber laser depending on the pump laser parameters and ways of pump wave coupling have been investigated. The competition between orthogonal polarization states has been also studied, and the single polarization regime of 0.5 mW power has been achieved.

The cascaded generation of a conventional dissipative soliton (at 1020 nm) together with Raman dissipative solitons of the first (1065 nm) and second (1115 nm) orders inside a common fiber laser cavity is demonstrated experimentally and numerically. With sinusoidal (soft) spectral filtering, the generated solitons are mutually coherent at a high degree and compressible down to 300 fs. Numerical simulation shows that an even higher degree of coherence and shorter pulses could be achieved with step-like (hard) spectral filtering. The approach can be extended toward a high-order coherent Raman dissipative soliton source offering numerous applications such as frequency comb generation, pulse synthesis, biomedical imaging, and the generation of a coherent mid-infrared supercontinuum.

Generation of regular pulses of linearly polarized radiation with periodic self-induced laser line sweeping by ~10 nm near central wavelength of ~1460 nm has been demonstrated for the first time in an all-fiber Bismuth laser without any tuning element. It has been shown that the radiation of each pulse is single-frequency, and the pulse-to-pulse frequency shift is as low as 1 MHz corresponding to one intermode interval in 100-m long laser cavity. The measured intra-pulse frequency chirp is below 1 MHz while the pulses are long (~10 μs) and overlapping. Thus the sweeping is nearly continuous in frequency and time domains.

This work reports on the development of a binary pseudo-random test sample optimized to calibrate the MTF of optical microscopes. The sample consists of a number of 1-D and 2-D patterns, with different minimum sizes of spatial artifacts from 300 nm to 2 microns. We describe the mathematical background, fabrication process, data acquisition and analysis procedure to return spatial frequency based instrument calibration. We show that the developed samples satisfy the characteristics of a test standard: functionality, ease of specification and fabrication, reproducibility, and low sensitivity to manufacturing error.

We demonstrate cascaded generation of first- and second-order Raman dissipative solitons in an all-fiber laser cavity. Optimization and coherent combining of dissipative soliton and second-order Raman dissipative soliton is performed.

Conventional (1015 nm) and Raman (1055 nm) dissipative solitons generated in an all-fiber Yb laser are mixed in an external photonic crystal fiber (PCF) at pulse energy of up to 4 nJ at the input. It has been found that red-shifted ~20 ps pulses with energy up to 1 nJ are generated in the parametric process. Their peak wavelength is tunable from 1084 to 1102 nm by means of the delay variation between the input pulses. At that, the parametric pulses are shown to be coherent with the input ones and compressible to ~2 ps that is useful in applications. The performed modeling explains the main features of generated pulses.

Energy of chirped dissipative solitons (DS) generated in fiber lasers may exceed a threshold of stimulated Raman scattering (SRS) leading to formation of a noisy Raman pulse (RP). As we demonstrated recently, a feedback loop providing re-injection of the Raman pulse into the laser cavity can form a Raman dissipative soliton (RDS) with similar characteristics to those of the main dissipative soliton. Here, we present the results of feedback optimization of the generated RDS spectra. First experimental results of coherent combining of DS and RDS are also shown.

Second harmonic generation (SHG) of a random laser operating at 1308 nm via Rayleigh backscattering in a phosphosilicate fiber with Raman gain has been studied. SHG power of < 100 mW at 654 nm has been obtained in PPLN pumped by ~7 W laser power. The SHG beam is stable, herewith its spectrum has no mode structure within ~0.5 nm bandwidth that is different from conventional Raman fiber laser with linear cavity. Direct comparison of SHG in two laser configurations demonstrates better parameters of the random laser having great potential for imaging and other applications requiring low-coherent visible light.

Traditional wave kinetics describes the slow evolution of systems with many degrees of freedom to equilibrium via numerous weak non-linear interactions and fails for very important class of dissipative (active) optical systems with cyclic gain and losses, such as lasers with non-linear intracavity dynamics. Here we introduce a conceptually new class of cyclic wave systems, characterized by non-uniform double-scale dynamics with strong periodic changes of the energy spectrum and slow evolution from cycle to cycle to a statistically steady state. Taking a practically important example—random fibre laser—we show that a model describing such a system is close to integrable non-linear Schrödinger equation and needs a new formalism of wave kinetics, developed here. We derive a non-linear kinetic theory of the laser spectrum, generalizing the seminal linear model of Schawlow and Townes. Experimental results agree with our theory. The work has implications for describing kinetics of cyclical systems beyond photonics.

Effects of intensity interactions (pump power depletion and sequential saturation of cascade generation) have been studied in a two-stage phosphosilicate Raman fiber laser in experiment and modeling. An analytical model of the laser which takes into account power variation along the fiber and spectral broadening of the first Stokes wave has been developed that describes experimental data both qualitatively and quantitatively. Good agreement between calculated and experimental values of the thresholds, differential efficiency for the first and the second Stokes waves and saturation levels for the residual pump and the first Stokes wave powers is demonstrated.