A nonmonotonic dependence of the stimulated Raman scattering (SRS) threshold of 240-fs second-harmonic pulses of an ytterbium fiber laser (515 nm, 3 Hz, up to 11 μJ/pulse) in organic glass (polymethylmethacrylate, PMMA) on C-H stretching vibrations has been discovered when moving the waist of the focused beam (lens F = 16 mm) from air into the sample volume. The first minimum of the threshold ( 2 μ J) was found when the waist combined with the surface. Here, the maximum intensity and the maximum value of the nonlinear refractive index (nonlinear lens) supported channeling of the pump in the medium at the maximum length of the SRS exponential gain, taking into account that half of the beam caustic was in air. The second minimum was achieved by moving the entire beam caustic, stretched along the beam axis because of spherical aberration, in a layer of 1.8 mm near the sample surface. Subsequent movement of the waist was accompanied by a five-fold increase in the SRS threshold due to conversion of a part of the pump pulse energy (515 nm) into the Stokes component (605 nm), the pulse of which was shifted forward because of dispersion of the refractive index and group velocities. This delay of the pump pulse destroyed the synergetic factor of action, which reduced the probability of a breakdown with a five-fold increase in pump energy. The delay reached a value of 480 fs at a PMMA sample thickness of 10 mm. The breakdown was observed with pump fluctuations in the vicinity of the minimum threshold (2 μJ) at the input surface of the PMMA sample.

Experiments on stimulated Raman scattering (SRS) in transparent polymethylmethacrylate excited by 240 fs laser pulses ($515 \mathrm{~nm}, \leq 11 \mu \mathrm{J} /$ pulse) have been carried out. We have discovered a non-trivial SRS threshold dependence on the distance from the laser beam focal plane to the sample front surface: a linear growth as the focal plane moved in the sample volume. The physical mechanism of such SRS threshold dependence is discussed.

A compact waveguide Tm:YAP laser with a pulse repetition rate of 8 GHz is developed. A controllable change in the intracavity loss provides continuous tuning of the central emission wavelength of the laser operating in the Q-switched mode-locking in the range from 1925 to 1950 nm, as well as makes it possible dual-wavelength lasing. The main approach of this study is the use of waveguide structures inside the Tm:YAP crystal and the saturable absorber based on graphene. This approach is universal for producing compact lasers with the gigahertz pulse repetition rate, operating in a wide spectral range.

This paper presents single-mode waveguide Nd:YAG laser passively mode-locked with graphene saturable absorber. Fine tuning of intracavity losses provides the possibility not only to adjust the mode-locking stability but also to controllably switch between single- and dual-wavelength operation.

A passive mode locking Nd:YAG waveguide laser with a gigahertz pulse repetition rate is presented. Single-layer graphene is used as the saturable absorber. A tubular waveguide in the active medium was developed to provide generation of only the fundamental transverse mode. Due to this approach, stable generation of pulses with a duration of < 20 ps and a repetition rate of 9.8 GHz was achieved.

We report a new solid-state waveguide laser generating picosecond pulses with a GHZ, repetition rate, based on the use of graphene as a saturable absorber. Lasing at the main transverse mode is provided by the geometry of a cylindrical waveguide formed in the active crystal volume by the method of direct writing with a femtosecond laser beam. Fine tuning of the intracavity interferometer formed between the active medium and output mirror makes it possible to control the spectral-temporal parameters of output radiation and to smoothly tune the repetition rate of pulses having a duration of less than 20 ps. In particular, the possibility of dual-wavelength generation in the regime of continuous passive mode locking using a single saturable absorber based on graphene is demonstrated. By amplifying laser output radiation in the ytterbium fibre amplifier, an average output power of 539 mW is obtained.

Distortions of the displacements measured by the heterodyne interferometer due to penetration of the electric excitation signal of the acousto-optic modulator into the path of registration and processing of optical signals are considered. The level of this type of noise is estimated and the ways of its elimination from data obtained using a three-coordinate heterodyne interferometer are proposed.

Предложен способ определения функций площади поверхности алмазных инденторов нанотвердомеров с помощью метрологического атомно-силового микроскопа с трехкоординатным лазерным интерферометром. Были проведены измерения формы граней ряда инденторов типа пирамиды Берковича. Точность измерения координат точек поверхности индентора составила 1 nm. Показано, что в процессе использования инденторов происходит изменение формы их вершины, в частности на первых 100 nm отклонение от идеальной пирамидальной формы может превышать 30 nm. Таким образом, одним из способов верификации функции площади поверхности индентора может быть периодическая поверка инденторов на метрологическом атомно-силовом микроскопе. DOI: 10.21883/PJTF.2017.03.44223.16487

A method for determination of the contact-area functions for diamond indenters of nanohardness testers using a metrological atomic-force microscope with three-coordinate laser interferometer is proposed. Face shapes of a number of indenters of Berkovich pyramid type are measured. The precision of the indenter surface coordinates measurement is 1 nm. It is demonstrated that the indenter tip shape changes in the course of its use; in particular, for the first 100 nm the deviation from the ideal pyramid can exceed 30 nm. Thus, one of the methods for verification of the contact-area function for an indenter is its periodic calibration using a metrological atomic-force microscope.

Test structures used for calibration of scanning probe microscopes have certain limitations. They are short-lived, their work surface becomes coated with microparticles over time, and it gradually wears out by contact with the measuring probe, resulting in the etalon geometry deformation. Dynamic etalons allow calibrating SPMs in ranges from pm to nm. In this article we present the results of dynamic etalon metrological characteristics research using an SPM equipped with tree-coordinate heterodyne laser interferometer. Obtained data indicates stability of piezoelectric modulus and absence of piezoelectric hysteresis phenomena in the etalon samples used.

Three-coordinate laser interferometer was designed to enable metrological measurements using conventional scanning probe microscopes. This article presents the results of the errors sources investigation in three-coordinate laser interferometer, describes the features of the optical scheme and data processing system that ensure sub-nanometer accuracy of the measurements.