We suggest using modulated self-injected radiation to achieve lasing regimes similar to Q-switching in a CO2 laser without loss of average output power. The feasibility of this solution is verified both theoretically and experimentally. Our theoretical model of CO2 laser is based on a standard six-temperature model supplemented with terms accounting for self-injection of laser output radiation. We show that temporal modulation of self-injected radiation with power several percent that of the laser output power in external optical systems achieves pulsed-periodical generation regime. The model is experimentally verified using a commercial CO2 laser. With modulation less than 5% of the output power pulsed-periodical lasing was realized. Pulse duration obtained was 300 ns with repetition rate of 20 kHz and power maximum-to-average rate around 20.
High-power lasers are useful instruments suitable for applications in various fields; the most common industrial
applications include cutting and welding. We propose a new application of high-power laser diodes as in-bulk heating
source for food industry. Current heating processes use surface heating with different approaches to make the heat
distribution more uniform and the process more efficient. High-power lasers can in theory provide in-bulk heating which
can sufficiently increase the uniformity of heat distribution thus making the process more efficient. We chose two media
(vegetable fat and glucose) for feasibility experiments. First, we checked if the media have necessary absorption
coefficients on the wavelengths of commercially available laser diodes (940-980 nm). This was done using
spectrophotometer at 700-1100 nm which provided the dependences of transmission from the wavelength. The results
indicate that vegetable fat has noticeable transmission dip around 925 nm and glucose has sufficient dip at 990 nm. Then,
after the feasibility check, we did numerical simulation of the heat distribution in bulk using finite elements method.
Based on the results, optimal laser wavelength and illuminator configuration were selected. Finally, we carried out
several pilot experiments with high-power diodes heating the chosen media.
Laser speckle analysis is a very powerful method with various existing applications, including biomedical diagnostics. The majority of the speckle applications are based on analysis of dependence of scattered light intensity distribution from sizes of the scattereres. We propose a numerical model of speckle formation in reflected light in one-dimension which shows that properties of the scattered light are strongly dependent on the form of the scatterers. In particular, the dependence of number of speckles from the size of the scatterers was investigated for the light reflected from the surface with varying roughness; the single roughness on the surface was assumed to have the form of one-dimensional ‘pyramid’ with the sides having either linear or parabolic descent from the top of the ‘pyramid’ to the bottom. It was found that for the linear roughness, number of speckles decreased with increase of the roughness size, whereas for the parabolic roughness the number of speckles increased. Results of numerical simulation were compared with experiment investigations of roughness samples (0.5-2.5 μm) made of glass and copper. Due to different production processes, the glass samples are likely to have the parabolic roughness and copper samples are likely to have the linear roughness. Experiments show that the dependences of number of speckles also have different slopes, the same as in numerical simulation. These findings can lead to new analytical methods capable of determining not only the size distribution of roughness (or scatterers) but also the shape.
We consider a problem of direct synthesis of the laser beam with predetermined intensity distribution, by means of intracavity adaptive optics. The mathematical formulation of the problem is reduced to the study of the solutions of the resonator equation, expressed in terms of the field amplitudes and phases inside the resonator, and the parameters of resonators that includes the deformable mirror. It is shown that, with some assumptions, the shape of the deformable mirror can be expressed as a function of the output intensity distribution. The results of direct numerical simulations agree with the obtained analytical estimates. Experimental verification is in progress.
Paper presents results of own development in the field of organic recording media for working (WERM) and archives (WORM) optical memory. Recording media for working optical memory have been prepared with the use of original thermally irreversible photochromic compounds from diarylethenes and fulgimides as well as polycarbonate as a polymer binder. Using these recording media, refractive and fluorescent methods for nondestructive readout of optical information have been elaborated. Aiming at making recording media for archives optical memory organic compounds (chalcone, diarylethene) which formed fluorescent products during irreversible photochemical reaction under laser irradiation were used. Based on developed photochromic materials samples of three-layer photochromic recording media have been prepared and tested with positive results on the developed optical device. This device includes Nd - laser and provides generation of several harmonics of laser irradiation.
The method of measurement of thermo-optical distortions (a thermal lens) in the active element Nd:YVO4 arising under axial diode pumping which distinctive feature is simplicity of processing and speed of reception of results of measuring have been described. Investigations were realized by means of Hartmann method based on monitoring of parameters of pumping radiation wave-front passing through investigated optical element. It is shown, that the proposed method enables direct investigation of thermo-optical distortions in small pumped areas (hundreds and tens micrometers). Presented is a method for research of thermo-optical distortions in an active element ensuring direct measurement of high orders aberrations.
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