Multisectional KrF laser with a pulse repetition rate of 4 kHz and inductive -capacitive discharge stabilisation

摘要

An electric-discharge KrF laser with an inductive capacitive discharge stabilisation and a pulse repetition rate up to 4 kHz is developed. The multisectional discharge gap with a total length of 25 cm is formed by 25 pairs of anode cathode plates. A discharge width of no more than 1 min is realised. Ne and He are used as the buffer gases, and F-2 serves as the fluorine donor. The maximum output pulse energy is similar to 6 mJ for the Ne-Kr-172 mixture at a total pressure of 1.6-3.2 atm. The maximum efficiency of the laser is similar to 1.4%. An original optical technique is worked out for measuring the gas velocity in the working gap. The maximum gas velocity in the gap between the electrodes is found to be 19 m s(-1) in the experiments. The average output power of the laser for a pulse repetition rate of 3-4 kHz is similar to 12 W, while the relative rms deviation of the laser pulse energy lies in the range 2 % - 3.8 %. It is shown that the refractive index gradient of the active medium, which is related to the free electron concentration in the discharge plasma, plays a significant role in the formation of laser radiation field in the resonator. The characteristic value of the refractive index gradient is found to be no less than 10(-5) cm(-1) for the KrF laser wavelength.