Non-Stationary Photovoltage in Materials Science of Wide Band-Gap Semiconductors of Modern Adaptive Optics and Optoelectronics

Bulletin of the Lebedev Physics Institute - Non-stationary photovoltage excitation in silicon carbide and gallium oxide crystals is studied. The signal transient responses are measured, and the...     

Amplitude autocorrelation of femtosecond laser pulses using linear photogalvanic effect in sillenite crystals

We demonstrate excitation of the linear photogalvanic current in a Bi₁₂TiO₂₀ crystal by two orthogonally polarized femtosecond laser pulses with detecting the electrical current via charge accumulation on the sample electrodes. Such a setup was used to implement an interferometric autocorrelation technique for characterization of ultrashort light pulses. Integration of the detected current in femtosecond time domain leads to vanishing of a bipolar component of the photogalvanic current which arises due to a pulse chirping. The advantage of the proposed technique is that it produces the electric field correlation function directly without the need for data processing using a compact, robust, and non-expensive detector in the form of a photoconductive cell of a non-centrosymmetric crystal.     

Polarization of Fluorescence of Excimer Vinylpyrene

The polarization of the excimer luminescence of copolymers of 1-vinylpyrene with methyl methacrylate has been studied. The obtained polarization dependences in absorption and fluorescence spectra differ for luminescence in the region of the maximum of the excimer band and of its longwave portion, which is due to the influence of the nonequilibrium configurations of the dimeric complex on the polarization properties of its luminescence.     

Sensing of multimode-fiber strain by a dynamic photorefractive hologram

We present a strain sensor in which a multimode fiber is used as a sensitive element. High sensitivity to dynamic strains is achieved by means of vectorial wave mixing in a photorefractive CdTe:V crystal. It was found that the largest source of noise in our sensor is related to the instability of the polarization state of speckles emerging from the fiber. This noise is significantly diminished in fiber with a core of large diameter (550 microm).     

Linear photogalvanic current excited in sillenite crystals by femtosecond laser pulses

We observe electric pulses generated in sillenite crystals (Bi₁₂SiO₂₀ and Bi₁₂TiO₂₀) by 100-fs laser pulses at the wavelength of 400 nm (below the band gaps of both crystals). The peak value of the current pulses scales linearly with the intensity of laser pulses up to ∼45 GW/cm². The direction of the induced current depends on the polarization state of the laser pulse. This polarization dependence and features of the current detection via charge accumulation at the sample electrodes allow us to conclude that the electric pulses are generated due to the linear photogalvanic effect.     

A multichannel adaptive interferometry system

A multichannel adaptive interferometer based on dynamic reflecting holograms multiplexing in a photorefractive crystal of cubic symmetry is proposed. The efficiency of hologram multiplexing is studied theoretically and experimentally. For the recording geometry used, a crosstalk between channels is shown to be less than the single-channel inherent noise for a wide angular range of beams entering the crystal, and the sensitivity depletion in one channel is insignificant for a large number of channels.     

Developing Physical Bases for Low-Frequency Acoustic Tomography in the Arctic Shelf Using Fiberoptic Geophones

Principles of the design and operation of a fiber-optic geophone based on a Mach–Zehnder interferometer for seismic monitoring of the Arctic Shelf when there is an ice cover are considered. The proposed approach to geophone design is based on the combined application of interferometric means of measuring and the spatial localization of the fiberoptic interferometer. The results from field experiments to test geophone prototypes are presented. It is shown that the seismic receiver’s threshold sensitivity of 10^?7 m s^?2 allows the recording of weak seismic signals in the area of the land–sea transition.     

Mobile adaptive holographic laser hydrophone

A mobile adaptive holographic laser hydrophone based on a dynamic hologram formed in a photorefractive crystal is developed. The hydrophone sensitivity is to –163 dB (rel. 1V/μPa) or 8.6 · 10^?3 rad/Pa in the frequency range of 1–15 kHz. Field tests of the hydrophone were performed in water area of a sea bay. The results confirm the efficiency of the use of measuring systems based on adaptive holographic interferometers to solve problems of recording weak signals (acoustic, hydroacoustic, and others) under non-laboratory conditions.