Table of contents

By the example of absorbing liquids (water, ethanol) irradiated by erbium laser pulses (λ = 2.94 μm), the possibility was experimentally demonstrated for detecting the displacement of the laser evaporation front by the phase shift (delay) of the acoustic response to a high-frequency (ω > 0.1 GHz) modulation of a laser pulse with the duration τ > 1/ω.

The review is devoted to high-power semiconductor lasers. Historical reference is presented, physical and technological foundations are considered, and the concept of high-power semiconductor lasers is formulated. Fundamental and technological reasons limiting the optical power of a semiconductor laser are determined. The results of investigations of cw and pulsed high-power semiconductor lasers are presented. Main attention is paid to inspection of the results of experimental studies of single high-power semiconductor lasers. The review is mainly based on the data obtained in the laboratory of semiconductor luminescence and injection emitters at the A.F. Ioffe Physicotechnical Institute.

We have fabricated and investigated linear arrays of single laser diodes (LDs) and epitaxially stacked double LDs based on AlGaAs/GaAs heterostructures emitting in the 808-nm range. The power — current characteristic of the double-LD bars has a slope of 2.18 W A^-1, which is almost twice that of the single-LD bars (1.16 W A^-1). The voltage drop across the former bars is also larger. At a pump current of 60 A, the output power of 5-mm-long arrays of LDs based on epitaxially stacked double heterostructures is 100 W under quasi-cw pumping, which is a factor of 1.8 above that of the single-LD bars under identical conditions.

The parameters providing suppression of the intersubband nonradiative relaxation between laser levels have been optimised based on the calculations of the potential profile and relaxation times for the active element of unipolar laser with strongly asymmetric (in height) barriers. The photoluminescence, photoluminescence excitation, and IR absorption spectra of a structure with a multiply repeated optimised active element have been investigated. The experimental data are found to be in good agreement with the calculation results.

A numerical technique for calculating the time-dependent multimode lasing in an electron-beam-controlled CO₂ laser at significant optical inhomogeneities caused by radiation self-action is presented. The reported calculations for subatmospheric pressure yield a sequence of involvement of transverse modes in lasing, the evolution of their characteristics (which is self-consistent with the evolution of gain and optical inhomogeneities of the active medium), and the exclusion of output modes from lasing. This calculation technique can be used when the radiation round-trip time around the cavity is shorter than the characteristic time of change in the active-medium characteristics.

AlGaAs/GaAs double laser heterostructures containing two different active regions have been grown by metalorganic vapour phase epitaxy in a single growth process, and their properties have been studied. A typical slope of their power — current curves is 2.3 W A^-1, which is almost twice that for a laser diode (1.2 W A^-1). We demonstrate lasing of the emitter regions of the dual-wavelength lasers in the range 800 — 815 nm, with a separation between the peaks of ∼7 nm. The observed effect of pump current on the lasing wavelength of the active regions in the dual-wavelength and single lasers indicates that the emitter region farther away from the heat sink is more sensitive to pump current variations.

72-fs pulses are generated at the first Stokes component frequency upon stimulated Raman scattering in a barium nitrate crystal for the radiation of the Ti³⁺:Al₂O₃ laser with the pulse duration of 50 fs. The energy efficiency of conversion is 20%. The barium nitrate crystal was optically pumped by two consecutive orthogonally polarised chirped pulses with the following time compression of the Stokes radiation pulse.

Lasing of a miniature all-solid-state SRS laser based on a Nd³⁺:SrMoO₄ crystal with a LiF:F₂⁻-passive Q-switch is studied. The dependences of the laser and SRS self-conversion parameters on the initial transmission of the passive Q-switch are studied experimentally and theoretically. Simulation of the lasing kinetics has shown the possibility of nonlinear cavity dumping upon highly efficient SRS self-conversion of laser radiation. An increase in the active medium length from 1 to 3mm resulted in an increase in the energy of the output 1.17-μm SRS radiation from 20 μJ to record-high 60 μJ at the absorbed multimode diode pump energy of 3.7 mJ.

The possibility of increasing the efficiency of one-cascade 1.5-μm SRS lasing in a BaWO₄ crystal placed into an external SRS cavity and pumped by a nanosecond Nd:YAG laser at a wavelength of 1.34 μm is studied. Conditions that prevent energy outflow to the second Stokes SRS component with a wavelength of 1.78 μm are found, which allowed us to increase the efficiency of one-cascade intracavity SRS lasing at 1.53 μm up to 60% and the slope efficiency up to the quantum limit (∼80% at the SRS pulse energy up to 20 mJ). The use of pumping by laser pulse trains provided the possibility of increasing the 1.53-μm SRS radiation energy to 40 mJ in a three-pulse train.

Generation of an electrical signal (ES) is experimentally investigated in the interaction of the pulse of a non-chain electric-discharge HF laser with the bottom surface of a water column. It was found that the ES amplitude is influenced by thin water layers (water contacts) present in the system under study, which undergo mechanical action in the process of water column movement initiated by the laser. Approximately ten-fold increase in the ES amplitude is observed if the water layer is present in the gap between the end of the water cell and surface of the quartz plate covering the cell and having a contact with the top water column boundary, as compared to the case of the free top boundary. Possible reasons for the thin water layer influence on ES characteristics and for the mechanism for the second ES peak origin in collapsing of the vapour cavity produced during water volume explosive boiling under the laser radiation are qualitatively discussed.

Characteristics of a discharge-produced plasma (DPP) light source in the spectral band 13.5±0.135 nm, developed for Extreme Ultra Violet (EUV) lithography, are presented. EUV light is generated by DPP in tin vapour formed between rotating disk electrodes. The discharge is ignited by a focused laser beam. The EUV power 1000 W/(2π sr) in the spectral band 13.5±0.135 nm was achieved with input power about of ∼63 kW to the plasma at a pulse repetition rate ∼7 kHz . The results of numerical simulation are compared with the experimental data.

The problem of steady-state generation of a Gaussian partially coherent beam in a stable-cavity laser is considered within the framework of the method of expansion of the radiation coherence function in partially coherent modes. We discuss the conditions whose fulfilment makes it possible to neglect the intermode beatings of the radiation field and the effect of the gain dispersion on the steady-state generation of multimode partially coherent radiation. Based on the simplified model, we solve the self-consistent problem of generation of a Gaussian partially coherent beam for the given laser pump conditions and the resonator parameters. The dependence of the beam characteristics (power, radius, etc.) on the active medium properties and the resonator parameters is obtained.

A method for measuring the carrier envelope offset (CEO) frequency of the femtosecond frequency comb with a bandwidth of less than one octave by using a Fabry—Perot interferometer is proposed and experimentally demonstrated.

We report the fabrication of narrowband frequency-selective filters for the 1.5-μm telecom window, which include a single-mode polymer waveguide with a submicron Bragg grating inscribed by a helium-cadmium laser. The filters have a reflectance R > 98 % and a nearly rectangular reflection band with a bandwidth Δλ≈0.4nm. They can be used as components of optical multiplexers/demultiplexers for combining and separating signals in high-speed dense wavelength-division multiplexed optical fibre communication systems.

The possibility of controlling the kinematic parameters of ultracold neutrons (UCNs) is analysed by the example of a waveguide transfer and transformation of 2D images in ultracold neutrons and by the example of an increase in the concentration and deceleration/acceleration of ultracold neutrons during their transport in the waveguide with a variable cross section. The critical parameters of the problem are estimated, which indicates both consistency of the proposed approach and the emerging experimental limitations.

We report techniques for the fabrication of laser radiation diffusers for interstitial photodynamic therapy. Using chemical etching of the distal end of silica fibre with a core diameter of 200 — 600 μm, we have obtained long (up to 40 mm) diffusers with good scattering uniformity. Laser ablation has been used to produce cylindrical diffusers with high emission contrast and a scattering uniformity no worse than ∼10 % in their middle part. The maximum length of the diffusers produced by this method is 20 — 25 mm.

Aleksandr Appolonovich Kazakov, a talented Russian scientist, professor, prominent organiser in the field of laser technologies, director of M.F.Stel'makh 'Polyus' Research and Development Institute, was 60 on 13 July 2010.

The 14th International Conference 'Laser Optics 2010' in which more than 800 scientists and experts from 35 countries took part, was held from June 28 to July 2, 2010, in St. Petersburg.