The research presents a multi-wavelength Cr:LiSAF laser. An intra-cavity Bragg grating facilitates wavelength control, achieving two non-commensurate wavelengths in free and passive Q-switch modes. Experimental results show a tunable range of 795 nm to 930 nm, minimal tuning step of 0.1 nm, and a 1.5 nm wavelength difference.

The work is devoted to the implementation of methods for improving the quality of recognition of objects and defects with sizes of the order of $10-100$ microns. To achieve this goal, it is necessary to consider both filtering the reconstructed image and the original digital hologram, and filtering the intermediate data (for example, the wrapped phase difference).

We report the results of a study of laser-induced transparency under the conditions of the optical Stark effect in CdSe nanoplatelets. The induced absorption spectra are measured by the pump-probe technique. Laser-induced transparency is observed due to the transfer of the population of the electron states of the valence band to the conduction band as a result of two-photon optical transitions under the action of pump radiation. The transparency of the medium is maintained for the lifetime of the first excited exciton level, which corresponds to 180 ps. The presence of a hypsochromic shift of the exciton absorption band by 3.1 meV for a pump power density of 39 GW/cm2 with the coincidence of pump and probe pulses due to the optical Stark effect is demonstrated. The results of fundamental studies presented in this paper can find application in the development of new photonic devices for controlling light with light.

A comprehensive view of the problem of optical interaction of radiation developing in systems with several cavities is presented. Static and dynamic gratings in the lasers based on narrowband and broadband active media are considered. A number of practically implemented systems are shown and fundamental limitations are indicated.

The laser source with dual wavelengths, with tunable distance between them simultaneously generating is demonstrated. The possibility of using it for a two wavelength holography is shown. Dual wavelengths at 890.7 nm and 906.7 nm provides measured accuracy of 3d surface profile at 25 µm,

The comparison of the influence of intra-cavity spectral selectors: static Bragg gratings and dynamic gain gratings, has been presented. It has been shown that their effect on the spectral properties of the laser radiation with a loop resonator is similar. The performed statistical study of the mode composition of the groups of the generation pulses at the Q-factor modulation mode allows us to conclude that the rewriting of the grating by the subsequent group pulse does not prevent radiation at the same frequency. This opens up the possibility of frequency stabilization of the radiation. The presence of an intra-cavity Bragg grating causes an increase in the probability of preserving the radiation frequency in neighboring pulses of the radiation group. It has been shown that there is a narrowing of the pulse generation spectrum in the group, despite the fact that the spectral width of the grating exceeds the spectral width of the generation pulse. The combined operation of static and dynamic intra-cavity gratings makes it possible to create a line of lasers with high pulse energy, radiation quality close to the diffraction limit, high peak power, and a narrow radiation spectrum.

Subject of study. A digital holographic system for layer-by-layer control of component quality in additive manufacturing able to determine the size and depth of defects on the surface of each layer was investigated. Method. The digital holographic system for layer-by-layer control of component quality in additive manufacturing operates based on a two-wavelength holographic interferometry method. The digital holographic system is based on a Michelson interferometer. The considered method involves recording holograms of the surface of each component layer at two adjacent wavelengths. As a result of hologram reconstruction, the complex amplitudes of the object wave in the reconstruction plane are determined, which, in turn, define the phases of the waves and their difference. The wave phase difference allows the depth of the defect on the component layer surface to be determined. A tunable diode laser and camera based on a CCD matrix are used as the radiation source and detector, respectively. Main results. The results of the investigation of the surfaces of additively manufactured components using the two-wavelength holographic interferometry method are presented. The recognition of large irregularities is possible through expansion of the phase pattern. The detection of surface defects with the size of 25 mu m is demonstrated. The reconstructed surface of a component manufactured by laser sintering of successive layers using the M250 additive setup for selective laser sintering and the reconstructed surface of a millimeter-scale macroscopic object are presented. Practical significance. The possible use of the digital holographic system for component quality control in industrial settings, including those applying additive technologies, is demonstrated. The component quality criterion is the absence of defects (cavities or protrusions) with size larger than 25 mu m. (C) 2022 Optica Publishing Group

The experimental setup, based on a two-wavelength holography method is described. The possibility of recognizing defects of the order of 25 μm are demostrated. The ability of pulsed two- wavelength holography with 0 new inexpensive laser source is demonstrated.

Subject of study. The lasing spectra of a pulsed laser based on a Cr:LiSrAlF6 active medium are studied. Method. An intracavity transmission volume Bragg grating was used as the lasing mode on two aliquant wavelengths and wavelength tuning. The grating was recorded in a photo-thermo-refractive glass. Main results. For the first time in Russia, simultaneous narrowband lasing was demonstrated at two aliquant wavelengths in the band of 795-895 nm in a Cr:LiSrAlF6 crystal. The use of a volume transmission Bragg grating for continuous tuning of the central wavelength of the generated laser emission was demonstrated using additional feedback through a mirror with a high reflection coefficient positioned in the first diffraction order. Practical significance. Pulsed lasers with tunable wavelengths are applied in various scientific and practical applications including ecological monitoring of atmosphere conditions. The lasing at two aliquant wavelengths investigated in this study enables the design of high-power pulsed sources of terahertz radiation in the range of 15.5-27.1 THz. (C) 2022 Optica Publishing Group

Holographic interferometry is a well-established field of science and optical engineering. It has a half-century history of successful implementation as the solution to numerous technical tasks and problems. However, fast progress in digital and computer holography has promoted it to a new level of possibilities and has opened brand new fields of its application. In this review paper, we consider some such new techniques and applications.

A detailed statistical analysis was carried out, as a result of which the probability of retention the frequency of radiation of successive pulses was experimentally obtained. We demonstrate the effect of retention the frequency of radiation of Nd:YAG phase conjugate laser and determine the probability of retention the frequency of neighboring pulses in train.

We demonstrate electro-optic Q-switched solid state laser with Cr:LiSAF active medium. A single 50 ns pulse with 14 mJ of output energy is demonstrated. Simultaneous generation of several peaks with a step of 1.4 nm within the spectrum envelope with a full width at half maximum of 10.3 nm is demonstrated. For an electro-optic Q-switched mode a Pockels cell is used. Demonstrated laser can be used in differential absorption lidar systems.

Приведено сопоставление влияния внутрирезонаторных спектральных селекторов: статических решeток Брэгга и динамических решeток коэффициента усиления. Показано, что их влияние на спектральные свойства излучения лазера с петлевым резонатором аналогично. Проведенное статистическое исследование модового состава цугов импульсов генерации в режиме модуляции добротности позволяет сделать заключение о том, что перезапись решeтки последующим импульсом цуга не препятствует излучению на той же частоте. Это открывает возможность частотной стабилизации излучения. Наличие внутрирезонаторной решeтки Брэгга приводит к повышению вероятности сохранения частоты излучения в соседних импульсах цуга излучения. Показано, что наблюдается сужение спектра генерации импульса в цуге несмотря на то, что спектральная ширина решeтки превышает спектральную ширину импульса генерации. Совместная работа статических и динамических внутрирезонаторных решeток позволяет создать линейку лазеров с высокой энергией в импульсе, качеством излучения, близким к дифракционному пределу, высокой пиковой мощностью и узким спектром излучения. Ключевые слова: стационарная решeтка, динамическая решeтка, дифракционная эффективность, самонакачивающийся резонатор, обращение волнового фронта.

We demonstrate an instrument for high-precision measurements of parts manufactured with selective laser sintering systems. Operation concept is based on obtaining digital holograms of the surfaces of each layer of the part in the process of layer-by-layer sintering with subsequent processing of the obtained data and reconstruction of the internal structure and external surface of the part. Limitations of accuracy, field of view and spatial resolution are demonstrated. We demonstrate a system with less than 10 µm altitude spatial resolution with further improvement up to 1 µm. Field of view obtained is 300 mm2. Surface spatial resolution up to 100 µm is demonstrated. Compactability of system allows it to be installed in many laser sintering systems.

The paper presents experimental results on charging free-falling particles of titanium dust about 40 microns in size using femtosecond and nanosecond laser pulses. The results include the ratio of the achieved dust particle charge under various conditions: beam size, energy, and laser pulse duration. The effects of interaction of femtosecond and nanosecond charging are discussed.

The article presents experimental results on charging free-falling particles of titanium dust about 40 microns in size using femtosecond laser pulses, as well as comparing the results with earlier studies on particle charging by nanosecond laser pulses. The results include the ratio of the achieved charge of dust particles under various conditions: beam size, energy, and laser pulse duration. The problems of multiphoton ionization, the degree of nonlinear process, and the quantum efficiency of femtosecond charging are discussed.

This paper presented a comparison of spectral properties between the phase conjugate laser with and without intracavity reflecting Bragg grating. It is shown that the Bragg grating narrows the lasing spectrum from 20.7 pm to 5.3 pm.

The influence of reflective Bragg gratings that are formed in an active medium due to the spatial periodic modulation of gain on the spectral properties of lasing are investigated by an example of a pulsed Nd :YAG laser. It is shown that, at a certain choice of the formation regime of reflective gratings of gain, the lasing bandwidth can be reduced by a factor of 3-5, with a corresponding increase in the pulse energy and significant improvement of spatial beam quality.

The paper presents LiSrAlF6: Cr lamp-pumped laser. The possibility of tuning the central radiation wavelength in the range of 795-895 nm is shown. The passive Q-switching mode was provided by a saturable LiF: F2-absorber with an initial transmission of about 72%. In the single-pulse generation mode with a duration of 100 ns, the pulse energy was 3 mJ with a spectral width of 45 pm. The fundamental possibility of operating in the generation mode of two spectral components for the range of 865-885 nm is shown.