Peculiarities of single harmonic amplification upon generation of higher harmonics in a GaAs plasma

The peculiarities of amplification of a single harmonic (the 27th harmonic at 29.4 nm) of a femtosecond laser are studied upon frequency conversion in a GaAs plasma. The influence of experimental parameters (the intensity of a picosecond heating pulse, the delay between picosecond and femtosecond pulses, the distance between the laser beam axis and a target, etc.) on the efficiency of the resonance single harmonic generation is investigated. It is shown that single harmonic amplification had the resonance nature when the 27th harmonic frequency was tuned to the frequency of the corresponding transition of a singly charged GaAs ion with the high oscillator strength.