POWERFUL PULSED SINGLE-MODE ULTRAVIOLET

The large number of applications imposes strict, occasionally contradictory requirements on the parameters of modern ultraviolet lasers in regard to power (pulse power and average power), repetition frequency and duration of the radiation pulses, temporal and spatial coherence, radiation modes, stability of power, optical axis, and time-dependent characteristics, and, finally, in regard to the dimensions of the laser. Naturally, nil these requirements can hardly be met in the design of a single laser. But depending upon the designation of the laser, certain groups of requirements can be combined. The present article reports on some parameters of the radiation of a powerful pulsed ion laser operated in single-mode operation on the 346.5-nm line and designated for holography. The active medium of the laser is xenon on whose ion transitions powerful lasing was achieved in both the visible and the ultraviolet portions of the spectrum [2]. Owing to the combination of properties, the ion transitions in xenon are suitable for pulsed single-mode lasing, as confirmed by the communications of [3,4] concerning the construction of a pulsed xenon laser with an output power of 30 W in single-mode operation at a repetition frequency of 10 Hz. The conditions of lasing were optimized with active elements whose design resembles that shown in Fig. 1. The inner diameter of the discharge channel was 7, 9, or 11 mm and the total length of the active element amounted to 1300 ram. Cold indium electrodes and a gas storage system are the outstanding features of the design. Radiation is generated at three ultraviolet ion transitions in xenon at the wavelengths 366.9, 364.5, and 333 nm. The 364.5-nm !ine is the strongest of these lines. Figure 2 depicts the dependence of the radiation power upon the amplitude of the voltage pulse at the active element. The greatest pulse power was obtained with a voltage of 10 kV applied to the active element in which the discharge channel had an internal diameter of 9 ram. The dependence of the current resembles that shown in Fig. 2a, because the dependence of the discharge current upon the voltage is linear. Figure 2b depicts the dependence of the lasting pulse power upon the pressure in the active element. The figure shows that the optimum operating pressure in the active element having a discharge channel with the diameter 9 mm amounts to (7-10) �9 10 -3 torr. Though the rate at which the gas "hardens" is reduced by utilization of cold indium cathodes, the low pressure of operation can be maintained for an extended period of time only with the aid of a gas storage system consisting of a xenon generator and an electromagnetic metering device. The gas losses are periodically compensated for by gas admitted from the metering device in proportion to the depletion of the gas reserve in the gas generator. The metering device is manually switched on by the operator. The active element is placed into an emitter which consists basically of a holder for the optical system composed of two heads with at1 adjustment mechanism, the heads being joined by four Invar rods. Strength of the construction is obtained by intermediate lightweight flanges~ The mechanism is adjusted with proper regard for long-term stable adjustment of the resonator.