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A semi-analytical dimensionless formula is presented for predicting the period-one frequency of an optically-injected laser over a wide range of injection powers and positive detunings. The result shows that for any given injected optical power, there exists an optimal detuning at which the period-one frequency is maximized. The formula is applied to a tabletop optical injection system with a commercially-available quantum-well distributed feedback laser with previously unknown design parameters. By extrapolating the linearity of the period-one frequencies at zero-detuning and weak-injection regimes, the physical control parameters of the laser are approximated to the analytical formula for wide ranges of injection powers and positive detunings. The accuracy of the model is experimentally verified, achieving period-one frequencies as high as 84.7 GHz.

In recent years, the Industry 4.0 paradigm has gained special relevance, focused on the integration of smart structures to increase the efficiency of processes. Photonics, with laser advanced manufacture and light-based sensors, can offer great possibilities in this field. Within advanced manufacturing, femtosecond lasers allow inscribing different optical structures. Waveguides are one of the most widely used structures in photonic sensors. This work proposes the design, simulation and manufacture of symmetric cladding waveguides in optical fibers using the slit beam shaping technique. Cladding waveguides characterized by their low losses (0.21 dB/cm), quasi?step-index refractive index profile, and circular cross-section are used to couple evanescent light from the core of a single-mode fiber to each of the four cores of a multicore fiber. This work has been supported by the Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación (PID2019-107270RB- C21), the Ministerio de Educación, Cultura y Deporte of Spain (PhD grant FPU2018/02797), and FEDER funds.

A simple method to measure the length of optical fiber is proposed using microwave photonic technology. The length of fiber is measured according to the free spectral range (FSR) of the microwave photonic system. The measurement accuracy is only related to the accuracy of FSR measurement. The accuracy is further improved by introducing a reference fiber, and the method was verified in the experiment with 2–10 m single-mode fiber.

Two techniques for multielement analysis of liquid-droplet aerosol are compared, which are based on the spectral analysis of the radiation of a laser plasma generated in a laser breakdown (LIBS) or during laser pulse filamentation in a liquid droplet aerosol (R-FIBS). A liquid-droplet aerosol containing Na solution is used. It is shown that there are optimal delay times of the start of signal recording relative to the start of plasma generation, at which the signal-to-noise ratio is maximal, for both techniques. The dependence of the signal-to-noise ratio is derived for different laser radiation focusing deep into a liquid-droplet cloud for LIBS. The Na detection limits are determined for both methods.

A conduction cooled high peak power, narrow linewidth, and sub-nanosecond multi-beam laser as an excellent candidate for non-scanning lidar is demonstrated. This laser is based on master oscillator power amplifier (MOPA) scheme which consists of a pulse pumped Nd:YAG/Cr4+:YAG microchip laser as the master oscillator and a high efficient grazing incidence Nd:YVO4 slab amplifier, and the output beam is expanded to 100 mm diameter by a 50× low aberration Galileo beam expander and then divided into a 50×2 staggered arrangement multi-beam array by a diffractive laser splitter. The laser operates at 1 064.28 nm with a spectral linewidth about 20 pm, which generates 1 mJ, 0.78 ns pulses at 7 kHz rate. The fluctuation of output power is less than ±2% when it works continuously for 1 h. The energy uniformity of the 100 sub-beams is up to 90%, the divergence of each sub-beam is about 20 µrad, and the total transmission efficiency of the diffractive laser splitter is more than 85%.

The amplifying dynamics of the pulse burst in Yb3+-doped fiber amplifier (YDFA) with high-power pulse pump is numerically analyzed by a finite-difference time-domain (FDTD) method. The numerical simulations show that the amplitude uniformity of the amplified pulse burst can be modified by adjusting the parameters of pump, such as relative delay and power. Though optimizing the pump parameters, we can reduce the gain difference between the pulses in a burst and improve the efficiency of coherent pulse stacking based on Gires-Tournois interferometers (GTIs). These results can be applied to the design of high energy ultra-short pulse amplifiers based on burst-mode amplification and coherent pulse stacking technology.

Results of experiments on the influence of the excitation mode on the CuBr laser pulse duration are described. One of the distinctive features of the research is the use of train pulses for CuBr molecule dissociation. The effect of the number of pulses in a train and the delay time between the last pulse in a train and an excitation pulse on lasing parameters is studied. It is shown that the variation in the delay time allows one to change the lasing pulse duration by more than three times.

In order to obtain excellent slow-light performance, we propose a photonic crystal waveguide (PCW) that introduces extrinsic defect rods in the center row of a complete square lattice rotated 45° counterclockwise and the second row adjacent to it. The continuous cavities are used as a storage of electromagnetic energy and a speed reducer of light speed, used for slow optical transmission in PCWs. Then, the plane wave expansion method (PWE) is used to study the slow light transmission characteristics of the proposed structure, and the influence of the structure parameters on the slow light performance is analyzed. Finally, the bandwidth is obtained at 23.37 nm when the normalized delay bandwidth product (NDBP) reaches 0.40. In addition, considering the effect of material properties on slow light performance, NDBP is further optimized to 0.44, and the bandwidth reaches 27.63 nm. A simple but universal structure is designed to provide an important theoretical basis for further improving the storage capacity with high bandwidth and high NDBP slow light.

Results of the numerical study of a possibility of compensating for aero-optical aberration distortions of the beam wavefront using the aperture sensing technique based on atmospheric backscatter signals are described. It is shown that the technique makes it possible to partially compensate for aero-optical aberrations. The cross section beam size becomes several times smaller than that of a beam without the wavefront adaptive control, and the intensity distribution becomes more symmetric about the optical axis.

Within this dissertation, several optofluidic devices are presented for applications in atom-optics and on-chip biosensing. Oxide-based optofluidic devices compatible with alkali vapors designed for all-optical atomic cooling and for slow and stopped light based photonic devices are presented. Also presented are polydimethylsiloxane-based optofluidic devices with single virus detection sensitivities. By controlling the liquid flow characteristics through such polydimethylsiloxane optofluidic devices, chip-based detection of single viruses is enhanced using hydrodynamic focusing and velocity multiplexing is demonstrated using a stacked-channel design. Lastly, a novel on-chip distributed feedback dye laser is presented which is fabricated with an integrated fluidic detection channel.

A photonic approach is proposed to generate microwave arbitrary waveforms based on the stimulated Brillouin scattering (SBS) effect and the Sagnac loop. The Sagnac loop is utilized to generate the optical signals of ±1st-order and ±3rd-order sidebands. Due to the principle of velocity adaptation, even order optical sidebands are suppressed. Thanks to the SBS effect, the microwave signal consisting of odd order harmonics is generated after the photodetector (PD), which can construct the triangular waveform, the square waveform, or the sawtooth waveform by adjusting the weight of the harmonics.

Optics has already established as a very successful information carrier for computation and communication both in analog and digital domain for its several salient advantages. In last few decades, there were found several approaches where optics was suitably used to get different coded data. Here, in this paper, the authors propose a complete all-optical system for getting the intensity varied Manchester-encoded data.

A method to evaluate the influence of the laser linewidth on the linearly frequency-modulated (LFM) signals generated by heterodyning two free-running laser diodes (LDs) is proposed. The Pearson correlation coefficient between the instantaneous frequency of the generated LFM signal and that of an ideal LFM signal is introduced to quantify the quality of the generated LFM signal. The closed-form solution of the correlation coefficient is given, which shows that the correlation coefficient is determined by the ratio of the LFM signal bandwidth to the square root of the total linewidth of the two LDs when the observation interval is fixed. Simulation results are also given, which proves the correctness of the theoretical results.

We report a Tm-doped noise-like mode-locked (NLML) pulsed fiber laser with a compact linear cavity which consists of dual nonlinear optical loop mirrors (NOLMs). The design of dual-NOLM shows both exceptional compactness in construction and distinct flexibility. In this laser, mode-locking can be realized through the nonlinear optical loop mirror technique. Stable noise-like mode-locked pulses with spectral bandwidth of 29.18 nm and pulse energy of 46 nJ are generated at a central wavelength of 1 999.7 nm. Our results indicate that such a simple and inexpensive structure can pave the way for the development of generating supercontinuum with desirable performance.

The developed and tested methods of dynamic control of micro-objects (MOs) of nuclear fuel, based on the reconstruction of spatial geometric characteristics of MOs along the contours of two-dimensional shadow projections, are considered. To describe the dimensions of the MOs, the overall dimensions and the average projected diameter are chosen, and their shape is described using the nonsphericity coefficient, which is defined as the ratio of the maximum overall size of the object to its minimum overall size. Metrological characteristics of control methods are given.

The possibility of reconstructing the spatial distribution of average air density in a supersonic jet from results of laser transillumination is considered. It is shown that the reconstruction procedure for axisymmetric flows can be performed based on Abel transforms by results of measurements of local wavefront tilts. An algorithm for reconstructing the average density of air in a medium from the deviations of the front of the transillumination wave relative to the jet axis is developed. The algorithm is tested in experiments on the vertical jet facility of the Institute of Theoretical and Applied Mechanics, Siberian Branch, Russian Academy of Sciences. The results agree well both with contact measurement data known from the literature and with the numerical solution of the hydrodynamic problem.

The work is devoted to the creation and research of a model of a laser pulse location (LPL) system without the use of an electron-optical converter (EOC) as an external shutter. The system is designed to detect light reflecting objects (LROs), including optical and optoelectronic surveillance devices. The description of the hardware and capabilities of the created special software is presented. The results of measuring the dependence of the signal on the LRO rotation angle relative to the direction of the optical axis of the LPL system, on the distance to the object, and on the aperture of its lens are presented. The light reflecting characteristics (LRCs) of typical video recording devices in real conditions were experimentally determined. A method for calculating the maximum detection range of LROs in the presence of information about their LRCs by measuring an informative signal at obviously shorter ranges with an increased degree of aperture is proposed and demonstrated.

The results of experimental and theoretical studies of the evolution of the small-scale transverse structure of high-power femtosecond laser radiation propagating in air in the multiple filamentation mode are presented. It has been found that the presence of intensity inhomogeneities in the initial transverse profile of the laser beam leads to the formation of spatially isolated light channels due to the Kerr self-focusing effect. When the power in these channels exceeds a certain threshold value (the critical power), radiation filamentation occurs in them. The parameters of these light channels are theoretically estimated on the basis of the diffraction-ray model of single filamentation. It is shown that for a laser beam with a centimeter radius and subterawatt power, the initial radius of intensity inhomogeneities in the transverse profile has a characteristic value of several millimeters.

An optical circuit is designed for the ring cavity of an optical parametric oscillator (OPO) based on two series-mounted active elements—mercury thiogallate crystals (HgGa2S4) with the radiation tunable in the near- and mid-IR ranges (4.75–9.07 μm). The dependences of the radiation idler wavelength on the phase-matching angle and of the distribution of the IR OPO output radiation intensity on the idler wavelength are derived. The possibility of narrowing the spectral width of the output radiation by introducing a dispersing element (Fabry–Perot etalon) into the cavity is considered.

In order to generate high quality regular optical vortex array (OVA), we present an experimental method for generating OVA using phase only liquid crystal spatial light modulator (LC-SLM) assisted two gratings. In the scheme, holograms of two grating are displayed on the screen of two LC-SLMs respectively; the diffraction optical fields are captured by a CCD camera. The simulated and experimental results show that the regular OVA can be generated by using double diffraction gratings. The generated OVAs have a constant topological charge of ±1. The method can provide a useful pathway to produce regular OVA for some applications in optical communication, particle trapping and optical metrology.

In order to implement 3D point cloud scanning of small hole structure, which could not be contacted or damaged, we propose a noncontact 3D measuring method. The system contains a laser triangulation displacement sensor, a Michelson interferometer system and a coordinate measuring machine, with the advantages of non-invasive scanning, fast measurement speed and high precision. Focusing on reconstructing 3D point cloud data, random sample consensus is used to separate surface data and hole data respectively from the raw dataset. Least square optimization determines the function of the cylinder, as well as hole diameter and inclined angle between the hole and the surface. In the experiment scanning a round hole, the estimated result has diameter error and angle error within 30 µm and 0.2°, respectively. Results manifest the effectiveness and feasibility of this system and express practicality in manufacturing industry.

In order to study the influence of backscattering of indicating laser in laser guidance process and laser guidance countermeasure test, the scattering function and volume extinction coefficient of typical aerosol distribution are calculated, and the backscattering detection model of 1.06 µm horizontally transmitted laser is established, based on Mie scattering theory and scattering function optimization algorithm; the model is used to study the change of backscattering energy detected by the detector at different positions and different detection angles, and the false-alarm area of laser guidance along the indicating laser path under different detection thresholds is obtained. The results can help to deepen the understanding of the influence of atmospheric scattering on the laser guidance process, and provide theoretical reference for the scheme design of the laser guidance countermeasure test.

A new version of the reflecting interferometer for $$S$$ -polarized light consisting of a thin metal film placed in front of a multilayer dielectric interferometer is considered. The appearance of narrow extremes in the spectral or angular dependence of the reflection coefficient depends on the location of the metal film in the node or antinode of the standing wave reflected from the interferometer (maxima or minima).

We present results of using a laser monitor with an independent illumination source (bistatic laser monitor) for imaging processes blocked from an observer by the background light. The maximal imaging speed was 15 × 103 fps. The possibility to observe the structural transformations in a combustion wave of self-propagating high-temperature synthesis is shown. A bistatic laser monitor is shown to allow significant improvement of the image quality (contrast and brightness) of low-contrast objects.

Problems associated with the radiography of objects made of steel having thickness of 100 mm and more are outlined. The classical method of gathering information provides for mounting semiconductor photo detectors directly on scintillators. As a result, gamma radiation scattered in a scintillator enters photo detector increasing the image noise and providing a negative effect on processing electronics. A method to design a recording system using a wavelength-shifting fiber having no disadvantages of the classical technique is proposed. This method makes it possible to decrease the image noise, to remove electronics from direct effect of gamma radiation and to increase the registration efficiency. Various approaches of implementing the method proposed to detect signals are explored experimentally with selecting the optimal techniques. This research enabled developing a design base to engineer recording element. The results on measuring parameters of the registering element are presented.

Electrically controlled light refraction in a nematic liquid crystal (LC) with homeoplanar orientation possessing different thicknesses has been investigated at angles of light incidence on the layers exceeding the angle of total internal reflection of an ordinary beam δo. The optical response rise and decay time dependences (τon and τoff, respectively) on the electric field and angle of light incidence δ on the LC layer are obtained for LC cells with thicknesses d = 7, 14, and 22 μm.

The transient current technique (TCT) is widely used in the field of silicon particle detector development. So far, only laser wavelengths with a photon energy larger than or similar to the silicon bandgap (single photon absorption) were used. Recently, measurements using two-photon absorption (TPA) for silicon detector testing have been carried out for the first time. Excess carriers are only created at the focal point of the laser beam and thus resolution in all three spatial directions could be achieved. The resolution perpendicular to the incident laser beam could be increased roughly by a factor of 10. First measurements using this new method were performed at the Singular Laser Facility of Universidad del País Vasco (UPV)/Euskal Herriko Unibertzitatea (EHU). Following the initial success of the method, a compact TPA-TCT setup is under development. A first description of the setup and laser system is presented in this article., This work was supported in part by the Spanish Ministry of Economy and Competitiveness (MINECO) under Grant FPA2013-48387-C6-1-P and in part by the Wolfgang Gentner Programme of the German Federal Ministry of Education and Research under Grant 05E15CHA.

The method of pulse laser location is studied in relation to the problem of detecting retroreflective objects, including optical and optoelectronic surveillance devices. Using the created mobile specialized hardware and software stand, the retroreflection indicators of typical video recording devices in real conditions were experimentally determined. The effectiveness of periodic illumination, frame accumulation, and the formation of difference images for the detection of objects in conditions of intense sunlight is demonstrated.

Numerical and experimental studies were investigated for the self-Q-switching Nd:LuAG laser which was achieved by the Kerr lens effect. By applying two output couplers of 6% and 1.4%, the shortest pulses of 193.4 ns and 5.1 ns were generated respectively while the corresponding repetition rates were 1.175 MHz and 96.15 MHz respectively. Related to the average powers of 3.34 W and 2.56 W, the system demonstrated the optical to optical efficiency of 21.87% and 21.1% for coupler of 6% and 1.4% respectively. The short pulses with the high repetition rates can be applied in many fields which demonstrate the high value of the research on this self-Q-switching laser.

Time-of-flight single-photon counting laser ranging offers an important tool for remote sensing and imaging. However, limited by the temporal properties of a single-photon detection and counting system, it encounters a challenge for high-resolution and high-precision distance metrology. Here, we incorporated dual-comb based laser ranging, an enabling technique for rapid distance measurements with high precision and large range ambiguity, with time-correlated single-photon counting (TCSPC) technology and demonstrated its feasibility for precise laser ranging under a photon-starved condition. Based on interferometric measurements of two asynchronous 2.8-pW, 25-GHz electro-optic laser combs with TCSPC, micrometer-level ranging precision was achieved for consistent distance measurements (a stand-off distance of 15.6 m) over several days. New opportunities might open up for high-resolution and high-precision single-photon counting laser ranging.

We report the generation of harmonic noise-like mode-locked pulses in a thulium-doped fiber laser. In this laser, mode-locking can be realized through the nonlinear polarization rotation (NPR) technique. The ring cavity configuration uses 5 m of a Tm-doped dual-cladding fiber, as a gain medium, pumped by a 793 nm diode laser. The cavity uses a couple of polarization controllers (PCs) and polarization-dependent isolator to form a nonlinear polarization-rotating saturable absorber. By carefully adjusting of the PCs, the laser generates noise-like mode-locked pulses at the 2.04 µm band. With the increase of the pump power, the laser generates harmonics of the mode-locking fundamental repetition frequency of 6.88 MHz, from which we can obtain the second harmonic in a controlled mode. The obtained results may be useful for enhancing the understanding of the mechanism and characteristics of noise-like pulse at the 2 µm band.

Results of the complex experimental study of the spectral and temporal characteristics of the emission glow of control samples of several solid-state substances (imitation of topographic targets in the atmosphere) and of solid aerosols (imitation of air pollutants) under the action of femtosecond pulses of a Ti:Sa laser (at a carrier wavelength of 800 nm) and nonlinear optical effects are presented.

An optical design of a novel structure has been proposed and demonstrated to perform photon recycling in a transmission-type laser-pumping white light. The structure includes a hemisphere reflector and a phosphor plate located at the center of a hemisphere reflector. The hemisphere reflector is not only used for photon recycling to increase the energy efficiency but also to keep the energy efficiency nearly unchanged when the number of the multiplexing laser increases. The experimental measurement shows that the photon recycling with the hemisphere reflector can increase the energy efficiency from 36.2% to 53.3% for on-axis incidence, and 35.2% to 55.7% for off-axis incidence. Besides, the efficiency keeps the same up to three-laser multiplexing in the experiment, and potentially can be extended to more than 10 in the simulation for various hole structures. The result is not only on the efficiency enhancement but also on the enhanced exitance of the laser white light and the unchanged etendue of the light source. This property is an important advantage for lasers rather than LEDs in a solid-state white light source.

The nonlinear optics of gigawatt power, 10 �m, 3 and 200 ps long pulses propagating in gases and semiconductors has been studied experimentally and numerically. In this work, the development of a high-repetition rate, picosecond, CO2 laser system has enabled experiments using peak intensities in the range of 1 – 10 GW/cm2, approximately one thousand times greater than previous nonlinear optics experiments in the long-wave infrared (LWIR) spectral region. The first measurements of the nonlinear refractive index of the atomic and molecular gases Kr, Xe, N2, O2 and the air at a wavelength near 10 �m were accomplished by studying the four-wave mixing (FWM) of dual-wavelength, 200 ps CO2 laser pulses. These measurements indicate that the nonlinearities of the diatomic molecules N2, O2 and the air are dominated by the molecular contribution to the nonlinear refractive index. Supercontinuum (SC) generation covering the infrared spectral range, from 2 – 20 �m, was realized by propagating 3 ps, 10 �m pulses in an approximately 7 cm long, Cr-doped GaAs crystal. Temporal measurements of the SC radiation show that pulse splitting accompanies the generation of such broadband light in GaAs. The propagation of 3 ps, 10 �m pulses in GaAs was studied numerically by solving the Generalized Nonlinear Schr�dinger Equation (GNLSE). These simulations, combined with analytic estimates, were used to determine that stimulated Raman scattering combined with a modulational instability caused by the propagation of intense LWIR radiation in the negative group velocity dispersion region of GaAs are responsible for the SC generation process. The multiple FWM of a 106 GHz, 200 ps CO2 laser beat-wave propagating in GaAs was used to generate a broadband FWM spectrum that was compressed by the negative group velocity dispersion of GaAs and NaCl crystals to form trains of high-power, picosecond pulses at a wavelength near 10 �m. Experimental FWM spectra obtained using 165 and 882 GHz beat-waves revealed an unexpected and rapid decrease in the FWM yield that was not predicted by the GNLSE model that accounts for third-order nonlinearities alone. These results suggest that the effective nonlinear refractive index of GaAs, having formidable second- and third-order susceptibilities, may be altered by quadratic nonlinearities.

A photonic method of highly reconfigurable microwave waveform generation based on time-wavelength interleaving has been proposed and experimentally demonstrated. By modulating multi-wavelength laser sources with Mach-Zehnder modulators (MZMs), multiple Nyquist pulses corresponding to different wavelengths are generated and overlapped with each other in the time domain. A dispersion compensation fiber (DCF) is used to separate these pulses due to the wavelength dependent delay. These pulses add together after photodetection and form desired waveforms. By controlling the wavelengths and powers of multiple laser sources, we can obtain various desired waveforms with tunable repetition rates and duty cycles. Experimentally, 9 waveforms including square, triangle, sawtooth, reversed-sawtooth and trapezoid with tunable repetition rates from 3 GHz to 6 GHz and duty cycles from 20.9% to 58.4% are obtained. This work demonstrates the great potential of incoherent time-domain synthesis for highly versatile arbitrary waveform generation.

Real-time observation of the emergence of coherent structures from noise via instabilities is of particular interest across disciplines ranging from biology to astrophysics. In the context of photonics, ultrafast fibre lasers provide an ideal test-bed for experimental observation of dynamical instabilities and generation of coherent structures of ultrashort pulses. Here we present experimentally obtained switch-on dynamics of counter-propagating ultrashort pulses in a bidirectional mode-locked fibre laser with delayed pulse formation via Q-switched and modulation instabilities, pronounced central wavelength drift, with the multiple-pulse formation. We define a localisation parameter using the round-trip resolved autocorrelation function to quantify the extent of the pulse formation, indicating an energy interchange between coherent features and background radiation. Furthermore, we report the formation of synchronised and unsynchronised dispersion waves. Our results reveal the complexity of the establishment of coherent features and their interaction with background radiation, contributing further towards the understanding of nonlinear systems in general. Emergent coherence in noisy, nonlinear systems of broad scientific relevance can be examined in real-time in optical analogues. Here, the complex dynamics of counter-propagating coherent pulses is examined, revealing how energy is exchanged between both channels and background radiation.

Main properties of holographic waveguide periscopic multiplexors of the exit pupil of optical systems of augmented reality displays are considered. Limitations in the operation of waveguide holograms, compensation of chromatic aberrations in periscopic schemes, and influence of waveguide defects on the operation of augmented reality displays constructed based on waveguide holograms are analyzed.

The techniques for alignment and quality checking of the primary 2.2-m diameter mirror of the Siberian lidar station (SLS) are suggested. The results of computer simulation of the field aberrations of the primary mirror are presented, and the area of the coma-free region is estimated. The spot diagram of the SLS primary mirror is measured based on the estimates of the image size of stars transiting through the zenith. Lidar signals are numerically simulated using ray tracing in the optical design program ZEMAX, accounting for the effect of the real spot diagram of the receiving optics. The shapes of the experimentally recorded and ray tracing simulated lidar signals are compared.

Based on a previously developed mathematical model describing the behavior of the window of a multi-kilowatt laser with an unstable cavity, the case of a two-component output window is considered. The two-component window consists of a transparent annular polycrystalline diamond and a central opaque area, separated by a plastic vacuum gasket. To reduce the heat load, the central opaque part is equipped with a cooler. Numerical calculations of thermomechanical processes for such windows used in high-power CO2 lasers are carried out. The mathematical model used for the calculations consists of three parts: thermophysical, mechanical, and optical. The advantages of the two-component design with a cooler being used with a multi-kilowatt gas laser are demonstrated. The dependences of the maximum admissible output radiation power, temperature distribution, and mechanical stresses on the window thickness are obtained. Conditions under which such an output window should not only successfully withstand the extreme radiation loads, but also ensure the minimum possible divergence of the outgoing radiation are considered.

The efficiency of retrieval of images distorted by atmospheric turbulence formed by single- and multiaperture systems is analyzed. It is shown in numerical simulation that the use of multiaperture observation systems for computer correction of atmospheric distortions under anisoplanatism can significantly reduce the exposure time. The main distortions are well corrected when imaging for a short exposure time, which corresponds to the case of a “frozen” turbulent medium. Correction of residual small-scale distortions requires an-order-of-magnitude shorter time than in the case of long-exposure imaging with the use of common single-aperture observation systems.

The designs of a warm (uncooled) aperture diaphragm in a gas-filled cryostat with a matrix photodetector sensitive in the infrared spectral range are studied numerically and experimentally. It is shown that for the chosen design of a warm aperture diaphragm, a $$384\times 288$$ pixel matrix photodetector is cooled by liquid nitrogen to operating temperatures (85 K) in less than 40 seconds, and by a throttle microcooler in 15 seconds, while maintaining the standard sensitivity of photodetectors based on cadmium–mercury–tellurium (CMT) structures.

—A wavefront corrector has been designed in the form of a cooled stacked-actuator deformable mirror for the correction of aberrations of laser radiation propagating through the turbulent atmosphere. The main parameters of this mirror are theoretically estimated. A technique for cooling the reflecting surface of the wavefront corrector through piezo actuators is suggested and experimentally tested. The main parameters of the deformable mirror are measured: the initial shape of the surface, the response functions of the actuators, the mirror stroke, and the frequency-amplitude characteristic of optical surface.

A reflective beam splitter is proposed and verified. The unit cell of the beam splitter is composed of a metal pattern, a dielectric substrate, and a metallic ground. Each subarray structure of the device is composed of four unit cells, which are gradually rotated at 45°. The horizontal and vertical subarrays form a 4×4 gradient metasurface supercell. In the operating frequency band, the incident linearly polarized terahertz wave is reflected and divided into four beams of approximately equal power but different propagation directions. The proposed terahertz beam splitter based on metasurface has the advantages of small size, low cost and easy processing, and can be applied to terahertz stealth and imaging.

In this paper, we use femtosecond laser pulse to scribe 304 stainless steel foil, detect the Fourier transform infrared spectrum of the sample before and after processing, confirm the “cold processing” and “thermal processing” and their mutual conversion, and determine the “cold processing” parameter window. The ablation threshold and incubation coefficient of 304 stainless steel foil are calculated, and the effects of scanning speed and effective pulse number on the ablation threshold are analyzed. The ANSYS software is used to simulate the radial and axial temperature distributions of the surface on 304 stainless steel foil sample and the heat-affected zone with a femtosecond laser fluence of 10 J/cm2 and an effective number of pulses of 1 200 are obtained. In the aspect of spectral detection, the Fourier transform infrared spectra of the sample before and after processing are measured and two processing mechanisms of “cold processing” and “hot processing” are confirmed, which proves that we can achieve the conversion between “cold processing” and “hot processing” by changing the laser fluence and determine the “cold processing” laser fluence range.

Time-resolved measurement enables us to reveal the dynamical evolution of the system. The ultrashort laser and pump-probe method provide a powerful tool for achieving the time resolved measurement. With the development of laser technology, e.g., Q -switching, mode-locking, chirped pulse amplification and the application of the Ti:Sapphire crystal, the pulse width of laser is getting shorter and shorter, and the pulse energy is getting higher and higher. It has brought tremendous changes to the field of optics and photonics. For example, in the 1980s, femtosecond (1 fs =10–15 s) lasers have been used to study the evolution of molecular intermediate states during chemical reactions, which revealed the dynamics of chemical reactions at the molecular level. Nevertheless, the electron inside atoms and molecules moves even faster on a timescale of “attosecond” (1 as =10–18 s). At the dawn of the 21st century, attosecond pulses were produced from the high harmonics generated in the interaction between intense femtosecond laser and novel atoms. In 2001, an isolated attosecond pulse with a duration of 650 as was produced in the experiment via a 7 fs few-cycle driving laser. In the same year, an attosecond pulse train with a duration of 250 as for single pulse was produced by a multicycle driving laser. These results marked that the pulse width of the laser broke through the femtosecond timescale, and opened the door to attosecond science. In the next decades, lots of ultrafast processes inside atoms and molecules, e.g., tunneling ionization, Auger decay of atoms and electron localization and internal charge transfer of molecules, have been invested by pump-probe measurement combining the attosecond pulses and few-cycle near infrared laser pulses. In addition, the applications of attosecond pulses have been gradually extended from gas to solid materials. By using the attosecond pulse, it is possible to manipulate the electron motion in the attosecond time scale, which corresponds to an extremely high frequency rate of petahertz. Such manipulation is considered to be the basis for developing the photoelectric information processing at petahertz. Attosecond science has become one of the most important achievements in the field of ultrafast optics in the past two decades. The crucial issue is the generation and control of attosecond laser pulses. Many schemes have been demonstrated to produce the isolated attosecond pulses. The most popular scheme is few-cycle driving laser, which requires carrier-envelope phase stabilized ultrashort laser pulse. On the other hand, since the generation efficiency of the attosecond pulse depends on the driving laser ellipticity, a polarization gating scheme has also been developed, which was later generalized to double optical gating. Another scheme is the two-color field scheme, which synthesizes the laser pulses with different wavelengths. The advantage of this method is that multi-cycle driving laser pulse can be used to produce isolated attosecond pulse. Recently, this method has been extended to the three-color cases. In addition, ionization gating and lighthouse schemes are also demonstrated in experiment. With these methods, the pulse duration of the attosecond pulse decreases gradually. At present, the shortest pulse width has reached 43 as and high power isolated attosecond pulse with a peak power of 2.6 GW has been produced. But how to improve the attosecond pulse energy and generation of circularly polarized attosecond pulses are still the hot topics currently.