Nikolai S Vorob'ev

Bimodal temporal distribution of photons in ultrashort laser pulse passed through a turbid medium

Abstract The criteria were determined for simultaneous observation of scattered and unscattered (ballistic) peaks in temporal distribution of a narrow pulsed laser beam passed through a strongly scattering medium. Conditions were found for such an observation on the basis of non-stationary two-flux model for radiation transport. Calculation results permitted the definition of a compromise between the parameters of the initial laser pulse and the properties of a scattering medium. This provided the separate observation of various types of photons. The theoretical calculations were confirmed by experiments on recording pulse profiles of passed radiation of fs-laser in a water–milk solution.

On the use of a chirped Bragg grating as a cavity mirror of a picosecond Nd : YAG laser

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.

Absorption and luminescence properties of Cr{sup 4+}-doped silica fibres

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 Cr{sup 4+} ions at 1100 nm at room temperature. The quantum yield of luminescence is estimated to be 10{sup -4}-10{sup -5}. (optical fibres)

Two-frequency tunable laser with electrooptic feedback

A two-frequency pulsed laser generating radiation with a sinusoidal profile was constructed. The probability of generation of sinusoidally modulated laser radiation with 100% modulation depth exceeded 80% and was independent of the frequency separation between the two emitted modes. This frequency separation could be tuned quasicontinuously from one shot to the next, which made it possible to vary the period of sinusoidal modulation between 6.6 ns and 300 fs. The simultaneous emission of two axial modes and Q-switched operation were ensured using an electrooptic feedback loop.

Anglo-Soviet Imacon 500 Streak/Synchroscan Picosecond Cameras Fitted With PV-001 Tubes

A series of Anglo-Soviet picosecond streak/synchroscan cameras was designed for application in various branches of science and technology. We are analyzing some of the most important steps in arranging of this joint camera production as well as briefly discussing further directions of our activity. Dynamic tests of mutually developed streak/synchroscan cameras are described.

Picosecond Image Converter Photonics & Its Applications In Semiconductor Structures Research

Present situation in picosecond image converter photonics is analized on the basis of the results obtained by the authors. Picosecond radiation sources are described as well as various approaches in image-tube photocathodes fabrication are discussed. Some new image converter cameras and CCD read-out devices will be introduced together with recent examples of their application in physics research.