Abstract: We have studied the properties of laser-induced microplasma (LIMP) emerging in the ablation of a strongly light-absorbing target in the regime of confinement of spatial plasma expansion. The LIMP particle temperature is shown to be higher in this case than in the free expansion. It is found that the amplitude of the pressure pulse in the regime of spatial LIMP confinement is an order of magnitude higher than in the open surface case. The feasibility of writing microstructures on transparent dielectrics with the use of LIMP is demonstrated: microlens arrays and different diffraction elements are made.

Abstract: This paper considers the effect of an ultrashort laser pulse on a thin gold film on a glass substrate at a focal spot size near 1 mm. We analyse the motion and thermal history of a film that has peeled off from the substrate in the heating spot as a consequence of melting. The detached zone is shown to form a domeshaped bump whose motion is hindered by surface tension. After the dome stops and turns back, towards the substrate, a jet begins to grow on its top. Concurrently, because of the heat dissipation in the film, melt recrystallisation begins, involving first the dome and then the jet. The liquid part of the jet elongates and breaks up into droplets because of the Plateau – Rayleigh instability development. The formation of a neck and the detachment of the last droplet occur in the solidification zone between the crystalline and liquid parts of the jet. The propagation of the crystallisation zone in the jet leads the necking process, so neck disruption occurs in the solid phase under nonequilibrium crystallisation conditions (the melt temperature is hundreds of kelvins lower than the melting point), at limiting mechanical stress and at high deformation rates. As a result, the jet transforms into a high needle with an extremely small tip radius (a

Abstract: A possibility of using self-phase modulation and cascaded quadratic nonlinearity effects for the enhancement of the temporal intensity profile is analysed theoretically in application to petawatt pulses at a kJ energy level. Preliminary experiments at a petawatt CETAL laser facility demonstrate the reduction of a pulse duration from 46 fs down to 29 fs by using the self-phase modulation effect and consequent spectral phase correction. These efficient methods offer an opportunity to economically enhance existing laser facility intensities and offer a broader range of high-intensity physics to become more readily attainable.

Abstract: Laser diodes based on AlGaInAs/InP heterostructures with an ultra-narrow waveguide are developed. It is shown that the use of this waveguide in conjunction with profiled doping ensures a balance between internal optical losses and heat resistance. Laser diodes with a stripe contact 100 μm wide demonstrate at room temperature an output optical power exceeding 4 W in a continuous-wave mode and exceeding 20 W in a pulsed mode.

Abstract: A combined optical parametric oscillator (OPO) with continuous tuning of the radiation wavelength in the spectral range 2.5–10.8 μm, optically pumped with the radiation from a Q-switched Nd : YLF laser (1.053 μm), is developed and tested. The oscillation is provided by an OPO1 based on a MgO : PPLN 'fan-out' structure in the spectral region 2.5–4.5 μm and by an OPO2 based on HgGa2S4 nonlinear crystals in the spectral region 4.18–10.8 μm, respectively. The angles of phase matching are measured for the HgGa2S4 crystals in the spectral range 4.18–10.8 μm for the type II conversion (eo-e), which virtually coincide with the calculated ones. The experimental absorption spectra of a gas mixture in the range 2.5–10.8 μm obtained using a gas-filled sealed-off photoacoustic cell are presented.

Abstract: The characteristics of modern microdisplays based on liquid crystals and electromechanical micromirrors are considered. These displays, being spatial light modulators, can rapidly generate large optical data arrays to be recorded as holograms and used for data processing. The potential of microdisplays for visualising digital holograms in real time is estimated.

Abstract: We report the results of the implementation of a quantum key distribution (QKD) network using standard fibre communication lines in Moscow. The developed QKD network is based on the paradigm of trusted repeaters and allows a common secret key to be generated between users via an intermediate trusted node. The main feature of the network is the integration of the setups using two types of encoding, i.e. polarisation encoding and phase encoding. One of the possible applications of the developed QKD network is the continuous key renewal in existing symmetric encryption devices with a key refresh time of up to 14 s.

Abstract: The efficiency of light scattering by nanoparticles formed using the method of picosecond laser ablation of silicon in water and by nanoparticles of mechanically grinded mesoporous silicon is compared. The ensembles of particles of both types possess the scattering coefficients sufficient to use them as contrast agents in optical coherence tomography (OCT), particularly in the range of wavelengths 700 – 1000 nm, where the absorption of both silicon and most biological and mimicking tissues is small. According to the Mie theory the main contribution to the scattering in this case is made by the particles having a relatively large size (150 – 300 nm). In the experiments on visualising the agar phantom surface by means of OCT, the contrast of the medium boundary, provided by nanoparticles amounted to 14 dB and 30 dB for the ablated particles and the porous silicon powder, respectively. The numerical simulation of OCT images of skin in the presence of nanoparticles, confirmed the efficiency of using them as a contrast agent.

Abstract: The possibility of increasing the power and efficiency of 3.5 – 5.0 μm optical parametric oscillators (OPOs) based on one or two ZnGeP2 crystals pumped by a repetitively pulsed Ho: YAG laser (λ = 2097 nm), which, in turn, is pumped by a thulium fibre laser (λ = 1908 nm), is studied. The OPO based on a tandem of ZnGeP2 elements is demonstrated to generate high-quality beams with an average power up to 10 W in pulses with durations of 15 – 25 ns at a repetition rate of ~17 kHz. The total conversion efficiency of the fibre laser power to the mid-IR radiation reached 25%. A theoretical OPO model explaining a cluster spectrum and higher output power in the case of the ZnGeP2 tandem than in the case of a single element is developed.

Abstract: In the course of in vitro studies of blood of laboratory animals with progressing Ehrlich carcinoma, we have revealed the change of the blood plasma optical properties in the THz range, which can be used for developing the express diagnostics of the presence of oncological diseases. An applied software package is elaborated that allows the phantoms of biological samples having a complex structure to be numerically simulated and the parameters of the electromagnetic wave reflected from these samples in the THz frequency range to be calculated.

Abstract: This paper describes the first experiments carried out on the GARPUN MTW Ti : sapphire – KrF hybrid laser facility and aimed at gaining insight into the interaction of subpicosecond UV pulses with solid and structured low-density carbon nanotube targets at peak intensities of ~1016 W cm−2 in a focal spot ~70 μm in size. Using X-ray absorbers, the plasma electron temperature has been measured to be ~850 eV. In our experiments, we used an optimal configuration: direct double-pass ultrashort-pulse (USP) amplification in KrF amplifier stages, with multiple laser beam filamentation suppression in a xenon-filled cell. The highest energy on a target was 0.25 J at a USP contrast relative to amplified spontaneous emission of ~3 × 1010 for intensities and ~3 × 105 for fluences. Owing to two-photon resonance in the UV spectral region, the use of xenon, with a negative nonlinear refractive index, allowed us to make the cross-sectional fluence distribution more uniform and reduce the beam divergence to 0.14 mrad (at the 10 % intensity level). Reducing the USP duration via negatively chirped pulse amplification and filamentation suppression and reducing the focal spot size on a target by using parabolic short-focus optics are expected to ensure an increase in the intensity incident on the target by one to two orders of magnitude.

Abstract: We have developed an ultrafast transmission electron microscope for studying dynamic processes in samples excited by femtosecond laser pulses and for probing transient processes occurring under irradiation by a pulsed (~7 ps) photoelectron beam with an adjustable delay with respect to the excitation pulse. A 75-keV photoelectron beam is formed using a silver photocathode irradiated by a femtosecond laser beam. This microscope is shown to have a high spatial resolution in the photoelectron regime: nanoscale in the imaging regime and atomic in the electron diffraction regime. It is used for experimental observation of ultrafast interaction of a laser-induced electron cloud with a pulsed photoelectron beam. Using this effect, a method of spatial and temporal alignment of excitation laser and probe electron pulsed beams on a sample is experimentally implemented.

Abstract: We demonstrate the possibility of inducing, erasing and extra rapidly controlling population difference gratings resulting from coherent interaction of unipolar subcycle pulses with a resonant medium. Gratings can be produced without overlap of pulses in the medium, which is an important distinction of the proposed approach from the traditional one, in which gratings are produced using interference of two or more overlapping quasi-monochromatic light beams. The use of unipolar subcycle pulses ensures faster control over gratings in comparison with bipolar pulses studied by us previously.

Abstract: Measuring the characteristics of radiation scattered by surface plasmon polariton waves and detecting them in the far field is the only efficient method for studying the directivity of propagation, wave vector magnitude, and propagation length of such waves. In the present work, we demonstrate that it is possible to control the properties of surface plasmon polaritons propagating along the surface of metal nanofilms by scattering from nanoobjects, namely, nanogrooves and nanopits, formed in the nanofilms. It is shown that this technique allows the main parameters of surface plasmon polaritons to be measured.

Abstract: We have studied the factors that reduce the efficiency of cladding-pumped ytterbium fibre lasers and amplifiers operating in the spectral range around a wavelength of 0.98 μm. It has been shown that the core of the active fibre being not single-mode leads to accelerated development of amplified spontaneous luminescence around λ = 1.03 μm, which reduces the highest possible amplifier efficiency. We have examined the effect of spontaneous luminescence propagating in the first reflective cladding. It has been shown theoretically that the pump-to-signal conversion efficiency is highest when the ratio of the core and cladding diameters in a multimode active fibre lies in the range 0.7 – 1. We have fabricated and characterised an optical fibre with a core-to-cladding diameter ratio of 0.76 (core and cladding diameters of 95 and 125 μm, respectively), which allowed a pump conversion efficiency of 66 % to be reached, a record level for cladding-pumped ytterbium fibre laser systems emitting near 0.98 μm.

Abstract: A broadband stigmatic (imaging) soft X-ray (λ > 120 A) spectrometer is experimentally realised. The optical configuration of the spectrometer comprises a plane grazing-incidence reflection grating with a spacing varying across its aperture according to a preassigned law [a so-called varied line-space (VLS) grating] and a broadband spherical normal-incidence mirror with an aperiodic Mo/Si multilayer structure. The average plate scale amounts to ~5.5 A mm−1. The radiation is recorded with a matrix CCD detector (2048 × 1024 pixels of size 13 μm). The line spectra of the multiply charged ions LiIII and FV–FVII excited in laser-produced plasma are recorded with a spatial resolution of ~26 μm and a spectral resolving power R ≈ 500 is experimentally demonstrated.