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

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 mm is realised. Ne and He are used as the buffer gases, and F₂ serves as the fluorine donor. The maximum output pulse energy is ~6 mJ for the Ne–Kr–F₂ mixture at a total pressure of 1.6–3.2 atm. The maximum efficiency of the laser is ~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 ms^-1 in the experiments. The average output power of the laser for a pulse repetition rate of 3–4 kHz is ~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.