We demonstrate that the temporal profile of the transverse nanoseсond photovoltage pulse generated in the thin
semiсonduсtor СuSe/t-Se nanoсomposite film under irradiation with elliptiсally polarized femtoseсond pulse is determined
by the interplay of linear and сirсular photoсurrents. These photoсurrents have different durations indiсating the
dependenсe of the relaxation time of the photogenerated сarriers on their spin. The interplay of photoсurrent results in the
generation of either unipolar or bipolar pulse with temporal profile dependent on the handedness, shape, and orientation
of the polarization ellipse of the laser beam relative to the plane of incidence.
Silver–palladium nanocomposite films are widely used in electronics. They exhibit a photoresponse sensitive to the polarization and direction of a wave vector of an incident beam. We present the results of experimental research of the effect of direct current bias on the pulse shape of the polarization- and wave vector direction-sensitive photocurrent in Ag/Pd nanocomposite films under nanosecond laser excitation at 532 nm. It is established that the direct current bias applied to the film excites an additional component of the photocurrent, independent of the sign of the angle of incidence, the pulse duration of which is much longer than the one of the polarization- and wave vector direction-sensitive photocurrent. It is shown that depending on the sign of the angle of incidence, the direct current bias may decrease or increase the amplitude, pulse duration, and fall time of the total photocurrent pulse. The obtained results show the ability to control the polarization- and orientation-sensitive photocurrent in Ag/Pd nanocomposite films using a dc voltage.
We report on a saturable absorption in aqueous dispersions of nanodiamonds with femtosecond laser pulse excitation at a wavelength of 795 nm. The open aperture Z-scan experiments reveal that in a wide range of nanodiamond particle sizes and concentrations, a light-induced increase of transmittance occurs. The transmittance increase originates from the saturation of light absorption and is associated with a light absorption at 1.5 eV by graphite and dimer chains (Pandey dimer chains). The obtained key nonlinear parameters of nanodiamond dispersions are compared with those of graphene and carbon nanotubes, which are widely used for the mode-locking.
An experimental approach for the direct measurement of the circular photocurrent (CPC) has been developed. The method was tested for the measuring the CPC due to photon drag effect in the Ag/Pd nanocomposites film in a wide spectral range. Measurements were performed at the wavelengths of 266, 532, and 1064 nm. The experimental results were compared with those obtained by the indirect conventional scheme. The obtained results open a new possibility of application of the Ag/Pd nanocomposites film to determine the direction of the electric field vector rotation of elliptically polarized light.
The optical limiting (OL) of detonation nanodiamond (DND) suspensions in engine oil was studied at a temperature range of 20°C to 100°C. Oil suspensions were prepared on the basis of the DNDs with an average nanoparticle cluster size in hydrosols (Daver) of 50 and 110 nm. Raman spectroscopy was used to characterize the samples. The OL investigation was carried out by the z-scan technique. The fundamental (1064 nm) and second (532 nm) harmonic radiations of YAG:Nd3+ laser with passive Q-switching as an excitation source were used. The OL thresholds for both suspensions at 532 and 1064 nm were determined. It is shown that a decrease in the average nanoparticle cluster size as well as an increase of the wavelength of the incident radiation leads to the OL threshold increase. It is established that the OL performance is not influenced by increasing the temperature from 20°C to 100°C. The results obtained show the possibility of using the DNDs suspensions in engine oil as an optical limiter in a wide temperature range.
Polarization influence on the photovoltaic current raised due to the photon-drag effect in the single-walled carbon nanotube (SWNT) films and nanostructured silver-palladium (Ag/Pd) resistive films is examined at the wavelengths of 532 and 1064 nm of nanosecond laser pulses. The SWNT films were synthesized by the aerosol chemical vapor deposition technique. Ag/Pd films, consisting of AgPd alloy and palladium oxide (PdO), were prepared by burning a special paste on a ceramic substrate. The films obtained were characterized by Raman spectroscopy. It is shown that the Ag/Pd films Raman spectra consist of PdO peak that moves from 650 cm−1 to 628 cm−1 as the excitation He-Ne laser power increases. The photocurrent was measured at the oblique incidence of the laser beam on the film in the direction perpendicular to the plane of incidence. It is found that the transverse photocurrent in the SWNT films at circular polarization is absent and does not depend on the direction of the electric field vector rotation (the sign of the circular polarization) of the incident irradiation. The photocurrent in the Ag/Pd films at circular polarized irradiation is significant and depends on the circular polarization sign. The results obtained demonstrate the potential applications of the Ag/Pd resistive films as a sensor of the circular polarization sign of the incident light pulse in a wide wavelength range.
We studied performance of a fast-response nanographite film photodetector (PD) in the temperature range of 300-
1000 K. In experiment, we measured the magnitude of the electric signal generated in nanographite film (NGF) under
irradiation of intense nanosecond laser pulses at λ=1.064 μm. In vacuum, the measurements of the PD sensitivity were
performed in the temperature range of 300-800 K. We showed experimentally that the PD sensitivity at 300 K was about
30% higher than that at 625 K and 50% higher than that at 740 K. At T>625 K, the magnitude of the light-induced signal
decreases as a linear function of temperature and vanish at T ≈ 1000 K. In atmospheric conditions, we observed a stable
operation of the NGF-based PD during several tens of hours in the temperature range from 300 to 580 K. However, at
higher temperature, degradation of the NG film resulted in a drop in the PD sensitivity.
The possibility of measuring the hydrogen impurity concentration in dense gas mixtures by coherent anti-Stokes Raman
scattering (CARS) is studied. In this technique, biharmonic laser pumping based on stimulated Raman scattering (SRS)
in compressed hydrogen is used. Because of the interference between the coherent scattering components from buffer
gas molecules and molecules of the impurity to be detected, the signal recorded may depend on the hydrogen
concentration by a parabolic law, which has a minimum and makes the results uncertain. It is shown that this uncertainty
can be removed if the frequency of the biharmonic laser pump, which is produced by the SRS oscillator, somewhat
differs from the frequency of molecular oscillations of hydrogen in the test mixture. A sensitivity of 5 ppm is obtained as
applied to the hydrogen-air mixture under normal pressure. The description of a set-up for the determination of the
coefficient of the hydrogen diffusion in gas mixtures is given. The main assembly units are a diffusion chamber and an
automated laser system for the selective hydrogen diagnostics in gas mixtures by the SRS-CARS method. The
determination of the diffusion coefficient is based on the approximation of the experimental data describing the hydrogen
concentration varying with time at a specified point in the diffusion chamber and the accurate solution of the diffusion
equation for the selected one-dimensional geometry of the experiment.
A simple high-speed photodetector of high-power laser radiation, based on the optical rectification effect in the nanographit film, is described. It operates without an external power source. The spectral dependence of the optical rectification effect in nanostructured carbon (nanographite) films obtained by plasmachemical deposition was studied in a wavelength range from 266 to 5000 nm. The performance of this device was demonstrated by detecting pulsed laser radiation using the second, third, and fourth harmonics of radiation from an YAG:Nd3+-laser with passive Q-switching, radiation from light oscillators based on stimulated Raman scattering in compressed hydrogen and parametric oscillator pumped by the second harmonic of the YAG:Nd3+-laser. It was shown that the photodetector response time is shorter than 0.5 ns. It is suggested that nanographite films are promising materials for detectors of ultrashort laser pulses in the IR, visible, and UV spectral intervals and for generators of electromagnetic radiation operating in the terahertz frequency range.
The photodetector based on optical rectification effect (ORE) was created using nanostructured carbon (nanographite) films. Sensitivity of the photodetector was studied in dependence on the carbon films size. It is shown that amplitude of electrical pulses generated by the photodetector depends on the thickness, length and width of the film area. The maximal sensitivity is reached at the film thickness of about 2.5 micrometers. It is shown also that the photoelectrical pulses appearing on the nanographite film have different nature than those appearing in on the silicon substrate.
Special features of the interaction of the powerful pulse laser radiation with films from graphite-like carbon material (layers of oriented carbon nano-tubes and plate-like graphite crystallites with the size of the nanometer order) were studied experimentally. After irradiation with 5 - 10 laser pulses for 22 ns on the wavelength of 1064 nm at a power density of 10 - 30 MW/cm2, the appearance of lengthy structural formations on the rough surface of the carbon film has been observed. The formations have a preferred direction perpendicular to the plane of the linear polarization of laser radiation, which is normal incident on the film surface. It has been shown that the carbon film treatment with circularly polarized laser radiation does not give rise to the appearance of oriented structural formations. The investigation of special features of the diffuse-scattered light from the surfaces of carbon films in the initial state and carbon films irradiated with laser was carried out. It has been established that powerful laser radiation gives rise to the appearance of a significant anisotropy in the indicatrix of the diffuse-scattered light from the surfaces of the irradiated films under study. The model was proposed, which explained the experimental results by anisotropic evaporation of the graphite-like carbon material occurring due to the essential polarization dependence of the absorption and reflection factors of light at large angles of incidence on an absorbing rough surface.
The possibility of the pulse laser radiation treatment of thin metal films on glass substrates has been studied experimentally. On the glass substrates with sprayed coating the diffraction structures were obtained due to the selective evaporation of metal at the interference of the powerful pulse laser radiation. The experiments were conducted using copper, aluminum films and films from titanium oxides. The thickness of the films on the glass substrates was 0.1 ÷ 0.12 μm. The regimes normally used during the film treatment with a laser beam were as follows: the wavelength was 1.06 μm, the pulse duration was 10 ns, and the enegy density of the beam was 10 mJ/mm2. To obtain an interference pattern on the treated surface the beam of the coherent radiation was preliminary split into two. In dependence on the convergence angle of the interference beams, the diffraction gratings had the lattice spacing in the range of 1 ÷ 6 μm. They were used to produce diffraction lenses. These lenses are a plane device with a ring-shape zone of concentric grating grooves capable to focus a certain part of incident radiation. In dependence on the wavelength, the radiation is collected on the optic axis at different distances from the diffraction lens. This fact makes it possible to use the lens in production of a simple monochromator. The structure of the diffraction gratings obtained has been studied, and their main characteristics and main spheres of their application have been determined.
Hydrogen emission processes from transformer oil under the electrical breakdown and low power ultrasonic where investigated by the method of coherent anti-Stokes Raman scattering. It was shown that low power of ultrasonic may be successfully used for degassing of transformer oil. The diffusion coefficient of hydrogen in transformer oil was measured.
The researches and data processing of laser pulse interaction with the surface of the target of aluminum alloy versus the air pressure and pulse power were carried out. The alloy 1420 is composed of 92% Al, 6% Mg and 2% Li. The industrial laser with pulse-half width of 3 ms was used to achieve the power density up to 2 x 106 W/cm2.
This study was made for measurement of hydrogen concentration in gas mixtures by coherent anti-Stokes Raman spectroscopy (CARS) with the aim of devising a technique for the detection of hydrogen-released from metals and insulating liquids exposed to a variety of external agencies. It has been found experimentally that under the fixed parameters of resonance biharmonic laser pump (BLP) the CARS signal of low constant hydrogen density essentially depends on the pressure of buffer gas. The obtained results are attributable to motional narrowing and broadening of the Doppler line of the Q01(1) transition of H2 in the gas mixture.
The bending of the channel of laser destruction in metals and dielectrics is observed experimentally. The plane of bending is proved to be perpendicular to the polarization plane of the incident laser beam. It is shown that the bending is a result of the polarization dependence of the light reflectivity from the surface of the channel, but not of the intensity asymmetry in the beam crossection. Such asymmetry is essential for the choice of direction of bending in its plane only. The experimental results are substantiated by the theory of light reflectivity from absorbing media, they are in qualitative and quantitative accordance with each other.
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