We propose and demonstrate an interferometric method of fabricating one-dimensional (1D) and two-dimensional (2D) periodic structures on planar substrates. The central idea of the method is to match the substrate or fiber translation velocity to that of the moving interference pattern so as to create its stationary image on the substrate or fiber. The moving interference pattern is produced by phase control of multiple interfering beams. The pitch of the structures can be changed by adjusting the frequency shifts between the interfering beams, and we demonstrate this pitch control technique in the case of interferometrically written 1D periodic structures. There is no limitation on the grating length, and grating designs can be arbitrarily complex optimized for use in both planar and fiber Bragg grating laser resonators.
We report tuning range and efficiency measurements of a novel dual-gain medium Brillouin/erbium fiber laser which utilizes the Brillouin gain in single-mode optical fiber and gain in erbium-doped fiber. Analytical results on the efficiency of the laser are presented which fit well to the experimental results and allow for an intuitive interpretation of the observed properties of the laser efficiency, which varies according to the laser operating conditions. Tuning range of 4nm was observed upon tuning of the Brillouin pump wavelength.
Evidence for different microscopic mechanisms of coherent photovoltaic effect in lead glass and semiconductor microcrystallite-doped glass is obtained by temperature studies of photoinduced second harmonic generation.
We report experimental studies of photoinduced second-harmonic generation (SHG) in lead glasses with different PbO concentrations. The dependencies of photoinduced second-harmonic saturation efficiency on PbO concentration and calculated third-order nonlinearity are observed. The optical concentration of PbO for photoinduced SHG is found to be approximately 50 wt%. Experimental results are interpreted on the base of photovoltaic model.
It is shown that second-harmonic generation efficiency in a photovoltaic model depends on the relationship of illuminated size to grating period. Model test experiments are proposed and realized. To explain the photo-induced second-harmonic generation (SHG) in glass optical fibers, two groups of models have been suggested, some based on separation of charges and appearance of a strong electrostatic field the others based on orientation of defects. However, a strong electrostatic field (approximately equals 104 V/cm) appears also in the last models. That is why neither the experiment on the discovery of such a field nor the experiment on the measurement of the component (chi)(2) tensor ratio gives an answer to the preference of either model. This paper shows that the efficiency of SHG by a (chi)(2) grating, resulting from a coherent photocurrent, depends strongly (approximately equals (r0/(Lambda) )-4) on the ratio of the transverse size r0 of the light beam, used for the grating preparation, and the grating period (Lambda). So we think that an experiment on SHG in a bulk sample to check this point will make it possible to clear up the mechanism of (chi)(2) grating formation. Another possibility is an experiment with the (chi)(2) grating writing by pump and second-harmonic waves, propagating in opposite directions in a fiber. In this case the grating period will decrease to (lambda)p/4 approximately equals 0.25 micrometers.
Photoinduced effects in optical waveguides are compared: photoinduced conversion of radiation polarization in lithium niobate optical waveguides and photoinduced second-harmonic generation in glass optical fibers. The cause of both phenomena consists in unusual interference between radiation with orthogonal polarization in one case and between radiation with a different frequency in the other one.
An x-ray preionized excimer laser is described. For this laser, the special sealed metal- ceramic x-ray preionizer with cold cathode was constructed. The cathode was made from carbon felt and had 4 X 80 cm2 area. The discharge volume was 70 X 4 X 3 cm3 and on XeCl one provided the energy up to 2J in a pulse. In the same discharge chamber, the different types of preionizers (spark discharges, UV laser radiation) were investigated. It was shown that the output energy depends on the electron density uniformity rather than the electron concentration.