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We present the results of measurements of low optical absorption and scattering coefficients in lithium triborate crystals using the method of piezoelectric resonance laser calorimetry under the action of polarised single-mode laser radiation at wavelengths of 1070 and 532 nm in the power ranges of 50 – 300 and 5 – 50 W, respectively. It is shown that when radiation propagates along the crystal axis a, these coefficients remain constant in the specified power ranges and do not depend on the direction of laser radiation polarisation. The measured optical scattering coefficients are compared with the results obtained by the method of integrating spheres.

We report the latest results on inscribing extended fibre Bragg grating (FBG) arrays upon fibre drawing, obtained at the Kotelnikov Institute of Radioengineering and Electronics of RAS. The properties of these structures are considered, and examples of their application in sensor systems of microwave dense wavelength multiplexing and as a basis for designing single-frequency fibre lasers are considered. The optical and laser characteristics of FBG arrays, inscribed (using 248-nm UV laser radiation) both in standard single-mode telecommunication fibres of the SMF-28 type and in erbium-doped active fibres, are investigated.

The properties of optical fibres with an array of fibre Bragg gratings written directly during the fibre drawing are considered. Such optical fibres offer new possibilities for producing new types of active and passive fibre elements due to the enhanced back-reflected signal of the so-called artificial Rayleigh scattering, and are of interest for modelling physical phenomena associated with the statistics of reflecting centres in optical fibres, such as, e.g., localisation of photons. We studied fibres with an array of Bragg gratings written in photosensitive fibres, ordinary single-mode optical fibre of the SMF-28 type and in fibre with a core doped with erbium ions. To control the spectrum width of the reflected signal, we used chirped phase masks, as well as writing arrays of gratings in tapered optical fibres.

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.

A PS-1/S1 picosecond streak camera with a linear sweep is used to measure temporal characteristics of synchrotron radiation pulses on a damping ring (DR) at the Budker Institute of Nuclear Physics (BINP) of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk). The data obtained allow a conclusion as to the formation processes of electron bunches and their 'quality' in the DR after injection from the linear accelerator. The expediency of employing the streak camera as a part of an optical diagnostic accelerator complex for adjusting the injection from a linear accelerator is shown. Discussed is the issue of designing a new-generation dissector with a time resolution up to a few picoseconds, which would allow implementation of a continuous bunch monitoring in the DR during mutual work with the electron-positron colliders at the BINP.

The first experimental evidence is presented that the use of a chirped volume Bragg grating (CVBG) as a cavity mirror of a Q-switched picosecond Nd : YAG laser with self-mode-locking leads to significant changes in the temporal parameters of the laser output. Measurements have been performed at two positions of the CVBG: with the grating placed so that shorter wavelengths reflected from its front part lead longer wavelengths or with the grating rotated through 180°, so that longer wavelengths are reflected first. In the former case, the duration of individual pulses in a train increased from ~35 to ~300 ps, whereas the pulse train shape and duration remained the same as in the case of a conventional laser with a mirror cavity. In the latter case, the full width at half maximum of pulse trains increased from ~70 ns (Nd : YAG laser with a mirror cavity) to ~1 ms, and the duration of individual pulses increased from 35 ps to ~1.2 ns, respectively, which is more typical of free-running laser operation.

The principles of simultaneous spatial and temporal focusing of photoelectron beams in nonstationary electric fields are theoretically studied and experimentally realised as applied to time-analysing image-converter tubes (ICTs). It is theoretically shown that the use of nonstationary focusing electric fields makes it possible to surpass the theoretical time resolution limit of ICTs (10−4 s) determined for stationary fields by Zavoisky and Fanchenko in the 40s—50s of the last century. The possibility of forming electron packets with an energy of 10–30 KeV and a subfemtosecond duration (below 10−15 s) gives impetus to the development of time-resolved electron diffraction, which is a direct method of investigation of atomic-molecular dynamics in solid and gaseous media.

The evolution of the phase delay between linearly polarised orthogonal modes in a spun fibre elastically twisted around its axis has been studied experimentally and theoretically using a model for a helical structure of the built-in linear birefringence axes. The phase delay is a sinusoidal function of elastic twist angle, with an amplitude and period dependent on fibre parameters: spin pitch and built-in linear birefringence beat length. It is shown that, at a known spin pitch, phase delay versus elastic twist angle data can be used to determine the beat length of built-in linear birefringence in the range 0.01 to 100 mm. The theoretical analysis results are supported by experimental data for conventional and microstructured spun fibres.

A PS-1/S1 picosecond image-tube streak camera (ITSC) with slit scan (streak camera), developed and manufactured at the General Physics Institute RAS, has been used to measure the spatiotemporal characteristics of ultrashort laser pulses generated by a petawatt-power laser installation 'FEMTO' at the Institute of Laser Physics Research in Sarov. It is found that such a camera is suitable for measuring the spatial and temporal parameters of single laser pulses with an accuracy of about one picosecond. It is shown that the intensity time profile of a train of picosecond pulses may be precisely defined for the pulses separated in time by a few picoseconds. The camera allows the contrast of radiation to be determined with a high (no less than 103) accuracy; spatial distribution of the laser pulses can be measured with an accuracy of tens of microns, and the temporal separation of single laser pulses can be identified with an accuracy of 1 – 1.5 ps.

We report a simple design of spun holey fibres and the first experimental study of the magneto-optical response of spun microstructured fibres with high built-in birefringence. Such fibres enable the Faraday-effect-induced phase shift to effectively accumulate in a magnetic field even at very small coiling diameters. For example, the magneto-optical sensitivity of a 5-mm-diameter fibre coil consisting of 100 turns is ~70% that of an ideal fibre, in good agreement with theoretical predictions.

An experiment has been proposed, theoretically substantiated and accomplished which has provided conclusive evidence in favour of one of two models for the behaviour of polarised light in optical fibres fabricated by spinning preforms with a high built-in linear birefringence (spun fibres): a helical structure of the built-in linear birefringence axes and circular birefringence. The experiment, carried out with a reflective fibreoptic dual-polarisation interferometer, has shown that the behaviour of polarisation states in spun fibres can be understood in terms of a helical structure of the built-in linear birefringence axes.

Laser-induced fluorescence is used for measuring the concentration of iodine molecules at the output of an electric-discharge generator of atomic iodine. Methyl iodide CH3I is used as the donor of atomic iodine. The fraction of iodine extracted from CH3I in the generator is ~50%. The optimal operation regimes are found in which 80%—90% of iodine contained in the output flow of the generator was in the atomic state. This fraction decreased during the iodine transport due to recombination and was 20%—30% at the place where iodine was injected into the oxygen flow. The fraction of the discharge power spent for dissociation was ~3%.

We report our experimental investigations of the formation and development dynamics of laser plasma produced in gas microvolumes (microplasma) upon multiple ionisation by tightly focused (to a spot 2—3 μm in diameter) high-intensity (up to ≈1017 W cm-2) femtosecond pulses of a Ti:sapphire laser (τp 130 fs, λ = 800 nm). Precision interferometric measurements (with a spatial resolution of ≈1.5 μm) were made of the spatiotemporal distribution of the refractive index and electron density in the microplasmas of the air and helium immediately during the action of the exciting femtosecond laser pulse and at the initial stage of free plasma expansion. The microplasma formation was shown to occur as a result of almost complete (up to bare nuclei) ionisation of the initial gas. For the first time the spectral continuum and the dynamics of spectral line formation in the UV and visible spectral ranges were investigated with a picosecond time resolution for the femtosecond laser-produced microplasmas of the air, N2, Ar, and He at normal conditions. For the first time the generation of the second (even) laser radiation harmonic was recorded in a femtosecond subcritical-density plasma of gases.

The propagation of laser radiation through a layer of a highly-scattering medium (HSM) is considered on the basis of two theoretical models: a nonstationary axial (two-flux) model and a nonstationary diffusion model. Analytic expressions for the temporal distributions of the photons of an ultrashort laser pulse transmitted through the HSM are presented. Experimental temporal distributions are used to obtain the parameters of models corresponding to an HSM, to determine the theoretical temporal distributions, and to compare them with the experimental curves. These two theoretical models are compared quantitatively for the first time. Their advantages and drawbacks that must be considered in the development of HSM transmission optical tomography are pointed out.

We propose a new method of temporal shaping of picosecond laser pulses using interference of chirped beams reflected from chirped volume Bragg gratings. This method is numerically simulated and experimentally tested. Quasi-rectangular picosecond pulses are experimentally obtained.

Long-period gratings are fabricated in an optical fibre for the first time by second-harmonic radiation from a femtosecond Ti:sapphire laser without the use of an amplifier. The photosensitivity of different fibres exposed to femtosecond pulses is studied. The estimates of the photosensitivity and the thermal properties of long-period gratings showed that the mechanism of the change in the refractive index induced by the 400-nm second-harmonic radiation differs from the corresponding mechanisms upon exposure to UV radiation from excimer lasers or irradiation by amplified 800-nm femtosecond pulses.

Generation of Stark spectral components in free-running Q-switched Nd:YAP (1064 nm and 1073 nm) and Nd:YAG (1062 nm) lasers is obtained. For this purpose reflecting volume Bragg gratings placed into the laser resonator and permitting to tune the laser emission spectrum were used. Stable generation of Stark components in both lasers is obtained. The possibility of obtaining two-frequency generation in an Nd-glass laser with the help of these gratings is shown.

The problem of enhancing the contrast of optical images in a strongly scattering medium by means of luminescent and absorbing dyes, topical in laser tomography, is examined. Preparations based on diphthalocyanine compounds were selected on the grounds of their tropism and resistance to the action of heat and light. Images with enhanced contrast in model scattering media (an aqueous solution of milk and margarine) were obtained in the IR region of the spectrum using the radiation of a picosecond neodymium laser. (laser applications and other topics in quantum electronics)

The conditions are identified for simultaneous observation of the peaks of scattered and unscattered (ballistic) photons in a narrow pulsed laser beam crossing a strongly scattering medium. The experimental results are explained on the basis of a nonstationary two-flux model of radiation transport. An analytic expression is given for the contribution of ballistic photons to the transmitted radiation, as a function of the characteristics of the scattering medium. It is shown that the ballistic photon contribution can be increased by the use of high-contrast substances which alter selectively the absorption and scattering coefficients of the medium.

An experimental investigation was made of the dependence of the optical density of a layer of a strongly scattering medium on its thickness in the case of a model aqueous milk solution. The radiation sources were IR lasers generating pulses of various (from nanosecond to femtosecond) durations. The dependences of the attenuation coefficients of such pulses on the solution concentration were determined for low and high optical densities of the solution layer. Estimates were obtained of the absorption and scattering coefficients of the medium. A modification of the two-flux Kubelka — Munk model was used to derive an expression describing the dependence of the transmission of a solution layer on its parameters when radiation detectors with a finite angular aperture are used. A comparison of the calculations and experiments revealed a forward scattering anisotropy of short-duration laser radiation in an aqueous milk solution.

A transient two-flux model of the interaction of light with a strongly scattering medium is developed on the basis of the concept of the paraxial photon propagating along the direction of thin pulsed laser beam incident on such a medium. An analitic expression for the radiation flux transmitted by a scattering medium is derived. Calculations are made of the dependences of the parameters of the temporal distributions of the transmitted radiation on the characteristics of the scattering medium. It is swown that the absorption and scattering coefficients of such a medium con be determined from the profile of the temporal distributions of the transmitted radiation. An experimental determination of the temporal distributions is reported for the radiation from a picosecond neodymium laser transmitted by a model scattering medium (a solution of dried milk in water). The experimental results are described well by the theoretical model.

The prototype of a passively Q-switched, longitudinally diode-pumped erbium glass laser is fabricated. A slope efficiency of 38% is achieved in the free-running lasing regime. It is shown that a pump energy of only 42 mJ is required to generate a 9-ns, 1.8-mJ output pulse with efficiency 4.2%.

The fibre fuse effect was observed for the first time in microstructured fibres exposed to laser radiation. The threshold power for this effect in such fibres is an order of magnitude higher than that for conventional silica fibres.

Continuous wave lasing is obtained for the first time in a flashlamp-pumped ytterbium ? erbium-doped glass.

A model constructed previously for plasma production through the laser heating, evaporation, and ionization of a microscopic surface defect is refined in an effort to determine the breakdown conditions in an aerosol. Simple analytic expressions are derived for the threshold laser intensity as a function of the wavelength of the laser light, the dimensions and material of the aerosol particles, the shape of the laser pulse, and the evaporated volume of the particle. The results are compared with experiments on the laser breakdown of air caused by beams from CO2 and Nd lasers in the presence of an aerosol consisting of carbon particles 0.1–25 μm in radius. The results are also compared with the predictions of the explosion model.

The absorption and luminescence spectra of silica fibres doped with chromium and various dopants are studied. Fibres doped with aluminium and gallium exhibit a broad (300 nm) luminescence band of Cr4+ ions at 1100 nm at room temperature. The quantum yield of luminescence is estimated to be 10-4-10-5.

The lasing parameters of active elements made of a new LGS-KhCh chromium — ytterbium — erbium glass are studied in the free-running mode. The methods for optimising the pump parameters and the laser design are demonstrated. An average output power of 8 W was achieved in a repetitively pulsed regime at the radiation divergence of 12 mrad at the 0.9 level.

An experimental investigation was made of the influence of an erosion plasma (formed from the target vapour) on the dynamics of a laser-supported detonation wave in the gas surrounding the target. The results confirmed self-consistent numerical model predictions of slowing down of a wave propagating under conditions of partial absorption of laser radiation. The observed effect was attributed to a reduction in the intensity of the radiation, reflected by the target surface and transmitted for the second time by the plasma, because of the absorption in the dense ionised vapour of the target material.

Experimental and theoretical investigations are reported of axial and radial shock waves formed in argon during propagation of an optical detonation wave maintained by a CO2 laser pulse. The experimental results are not be described by the standard self-similar law of motion of a cylindrical shock wave, but instead they agree well with the results of self-consistent two-dimensional numerical calculations. This is attributed to displacement of a hot gas along the beam axis out of the zone of absorption of laser radiation. The distance R travelled by the front of the resultant radial shock wave during a time interval t is described by the law R ∝ tα, where 0.55

An analysis is made of a model of the formation of a surface laser plasma which takes account of the heating and vaporisation of thermally insulated surface microdefects. This model is used in an interpretation of experiments in which such a plasma has been formed by irradiation of a titanium target with microsecond CO2 laser pulses. A comparison with the experimental breakdown intensities is used to calculate the average sizes of microdefects and their concentration: the results are in agreement with the published data. The dependence of the delay time of plasma formation on the total energy in a laser pulse is calculated.

A high space — time resolution is achieved in detection of radiation from a Ti:sapphire laser by the methods of femtosecond photoelectronics. A time resolution of 2 × 10-13 s is obtained at wavelength of 800 nm in a linear scan regime for a streak speed of 5 × 1010 cm s-1, an input power density of (1 — 5) × 103 W cm-2, and a linear dynamic detection range no more than 10.

Temporal separation of photons in an ultrashort laser pulse transmitted through a strongly scattering medium was reliably observed in experiments. The selected combination of the initial pulse parameters and of the characteristics of the scattering medium made it possible to ensure conditions necessary for the generation of a bimodal temporal profile of the transmitted radiation.