G. M. Mikheev

Giant optical rectification effect in nanocarbon films

We present observations of the optical rectification effect in the nanocarbon film, which is excited by nanosecond pulses of a Nd:YAG laser in the absence of an external electric field. Effective second order susceptibility of the film material is found to be 10−6 CGSE, which is higher than that of conventional noncentrosymmetric crystals. The measured ratio of the dc voltage to the laser power is 500 and 650 mV/MW at the wavelengths of 1064 and 532 nm, respectively. This makes the nanocarbon materials a promising alternative to conventional semiconductor-based terahertz radiation sources.

Polarization-sensitive photoresponse of nanographite

We report on polarization-sensitive direct current photoresponse of nanographite films in a 532–4000 nm spectral range. It is found that irradiation of the nanographite by the nanosecond laser pulses produces the electric current with intensity depending on the incidence angle and polarization of the laser beam. The obtained dependencies of the photoresponse on wavelength and polarization of excitation laser beam are discussed in terms of the surface photogalvanic and photon drag effects.

Photon-Drag Effect in Single-Walled Carbon Nanotube Films

We observed an interaction of single-walled carbon nanotube films with obliquely incident nanosecond laser radiation in visible and infrared regions generating unipolar voltage pulses replicating the shape of the laser pulses. The photoelectric signal significantly depends on the laser polarization and has maximum value at the laser beam incidence angle of ±65° and at the film thickness of 350 nm. The results are explained in the framework of the photon-drag effect.

Size effect on the optical limiting in suspensions of detonation nanodiamond clusters

We report on the optical limiting (OL) in stable aqueous suspensions of detonation nanodiamond (ND) clusters with average size of 50, 110, and 320 nm. The nanosecond Z-scan measurements at wavelength of 532 nm revealed that the larger the cluster size, the better the OL performance and the higher the ray stability of the ND suspension. Our analysis showed that the nonlinear scattering and the nonlinear absorption are the dominant mechanisms of OL in aqueous ND suspensions.

Nonlinear scattering of light in nanodiamond hydrosol

The nonlinear scattering of light under the conditions of optical limiting of nanosecond pulsed laser radiation at a wavelength of 1064 nm in a nanodiamond (ND) hydrosol has been experimentally studied. Superstable hydrosols were obtained from detonation NDs with a modified surface. Using an improved scheme of z scanning, it is shown that a decrease in the optical transmission coefficient of an ND hydrosol under optical limiting conditions is due to enhanced nonlinear scattering. It is established that the energy of pulsed radiation scattered at a right angle obeys a power law in dependence on the energy density of incident radiation pulses. Hydrosols of detonation NDs with the modified surface exhibit high stability with respect to the periodic laser action at high power density.

Nanographite analyzer of laser polarization

An optical analyzer of laser polarization has been designed and manufactured. The principle of operation of this analyzer is based on the recording of the polarization-dependent surface photocurrents in nanographite films. The analyzer does not contain additional optical elements and consists of a cylindrical bushing with a gauge of its angular position, a nanographite film grown on a silicon substrate, two parallel measurement electrodes placed on the film surface, and an electrical measuring instrument. The nanographite film is placed on the bushing obliquely so that the measuring electrodes are parallel to the axial cross section of the bushing, which is oriented perpendicular to the film tilt plane. The analyzer can operate in the wavelength range from 266 to 4000 nm.

Circular photogalvanic effect observed in silver-palladium film resistors

The surface circular photogalvanic effect (CPGE) at a laser wavelength of 1064 nm was observed for the first time in silver-palladium resistors fabricated by a thick-film technology. The CPGE response was detected using the electrodes oriented parallel to the radiation incidence plane, for the laser beam obliquely incident onto the sample surface. The coefficient of the pulsed laser radiation power conversion into light-induced emf (with the polarity depending on the sign of the circular polarization) amounted to about 80 mV/MW for film dimensions of 0.02 × 20 × 20 mm and a load resistance of 50 Ω. The maximum absolute value of the conversion coefficient was observed for the angles of light incidence of ±60°.

Light-induced EMF in silver-palladium film resistors

We have studied the generation of nanosecond emf pulses in silver-palladium film resistors under the action of radiation of a Q-switched laser. The samples were fabricated using the technology of thick film resistors on dielectric substrates, based on fusing a resistive paste that contains palladium, silver oxide, glass, and an organic binder into the substrate at 880 K. The amplitude of detected pulses exhibits linear growth with the power of incident laser radiation, depends on the angle of light incidence (vanishes at the normal incidence) onto the film and the angle of film rotation about the normal to its surface, and changes its sign with that of the incidence angle. The duration of the generated emf pulses is several times that of the incident laser pulses. The signal is not of a thermoelectric nature and can be related to the current generation by means of the surface photogalvanic effect and the photon quasi-momentum transfer to charge carriers during light absorption by the film material.

Quick-Response Film Photodetector of High-Power Laser Radiation Based on the Optical Rectification Effect

The efficiency of conversion of high-power laser radiation to an electric signal based on the optical rectification effect in nanographite films is studied experimentally. The amplitude of the signal is found to significantly depend on the size of the film, as well as on the length and arrangement of measuring electrodes. The maximal sensitivity of the photodetector (above 500 mV/MW at a wavelength of 1064 nm) consisting of the film with electrodes and operating without an external power supply and add-on components is shown to be achieved when the size of the film is comparable to the laser beam diameter. The sensitivity of the photodetector is studied under the condition when a nanosecond beam from a pulsed laser scans the surface of the film in two mutually perpendicular directions. The local sensitivity increases near the free ends of the photodetector. It is shown that the nanographite detector and a similar photodetector made of a polished silicon wafer have radically different parameters.

Effect of the burning temperature on the phase composition, photovoltaic response, and electrical properties of Ag/Pd resistive films

Silver-palladium (Ag/Pd) films were grown by thick-film technology using a resistive paste consisting of Pd, Ag2O, and glass on ceramic substrates at burning temperatures of 878, 1013, and 1113 K. The effect of the burning temperature and Pd content in the initial paste on the phase composition, resistivity, photovoltaic properties of films, free carrier concentration, and mobility was studied. It was found that the films grown at a burning temperature of 878 K have the greatest factor of conversion of the pulsed laser power to the photovoltaic signal, which depends on the direction of the incident radiation wave vector. Using X-ray diffraction, X-ray photoelectron spectroscopy, and thermodynamic modeling, it was shown that the AgPd alloy and PdO oxide are the main components of the Ag/Pd film with photovoltaic properties.