The crystal growth of GaAs is briefly reviewed, mainly by concentrating on the relations possibly existing between the growth conditions and stoichiometry and impurity content in grown crystals. Two prospective methods, recently developed, are also described.
It is found experimentally that the phase of gas lasers can be efficiently locked by means of cavity length modulation, but no theoretical explanation has yet been given. Under the assumption that 3-mode oscillations are always possible and that the parameter coefficients of Lamb's differential equations vary slowly with the displacement of the reflecting mirror, we obtained numerical solutions of these equations. It is found that the experimental results so far obtained agree with the present numerical results.
An infrared frequency standard stabilized with respect to the absorption line of methane has been constructed and studied. An extra-cavity cell of CH4, which is kept at the triple point or the boiling point of nitrogen, is used to stabilize the 3.39μm 3He-22Ne laser. 22Ne line is shifted by pressure effect and broadened by Zeeman effect resulting in a flat top in the gain curve at the center of the absorption line. First derivatives of the output power passing through the cell show approximately constant slopes near the line center in the CH4 pressure range 13-70 Pa (0.1-0.5 torr), and the control signal is not sensitive to the CH4 pressure in this range. Two servo systems with and without an integrator have been tested, and from the traces of the error signal, fluctuations of the stabilized frequency are estimated to be ±2×10-11 in a day and ±8×10-11 in an hour respectively.
An interface between a desk calculator and a digital voltmeter, which measures the pho-tocurrent of a spetral line, is constructed for the purpose of on-line integration of the inten-sity profile. No modifications are necessary either in the calculator or in the digital volt-meter. Tedious and time-consuming manual proce-dure for calculations is eliminated.
The output power spectrum of a laser beam modulated by two vibrating quartz crystals is studied experimentally and theoretically. When the azimuthal angles of the two crystals are set at 45 degrees from the optical polarization direction, the spectrum consists of fundamentals, second harmonics and sum and difference frequencies of the two modulation frequencies. We can select any one of these components separately by changing the azimuthal angles. The experimental data agree well the theoretical computation.
An apparatus equiped with hdrogen-filled thyratrons and trigger delay circuits is con-structed to from an almost rectangular light pules from two intense xenon flashes. The duration of this “square” flash can be varied from 50 to 150μ sec. This illumination unit makes the use of a blast shutter unnecessary and much facilitates the perormance of an ultra-speed framing camera.