Abstract
We demonstrate cryogenic Ti:sapphire single-pass amplification of sub-7 fs laser pulses with 80 MHz repetition rate. We amplify the output of a broadband Ti:sapphire oscillator by more than a factor of two, re-compress the pulses down to sub-7 fs, and show that the rms carrier-envelope phase jitter stays below 70 as after amplification. The amplified output exceeds 2 MW of peak power and 1 W of average power. In addition, we demonstrate amplification of ∼200 fs, 75 MHz oscillator pulses up to 1.6 W with a gain of four. This work opens a new way to explore phase sensitive and highly nonlinear phenomena at the full oscillator repetition rate. As a first example, we demonstrate white light generation in a bulk crystal at the full oscillator repetition rate.
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GENERAL SCIENTIFIC SUMMARY Introduction and background. Short pulse lasers emit trains of pulses with high repetition frequency, usually in the range of around 100 MHz, but maximum output power is limited. This is why laser amplifiers are frequently used. Often times the pulse energy is greatly enhanced, while the repetition rate is reduced drastically to around 1 kHz. This is not acceptable for many applications that require high repetition rates, such as femtosecond frequency combs used for precision spectroscopy, where a high repetition rate ensures that individual spectral modes of the laser can be resolved.
Main results. In our paper we show that we can efficiently amplify the output of a femtosecond laser oscillator with a liquid nitrogen cooled single pass titanium:sapphire amplifier at the full oscillator repetition rate. We show that the ultrashort pulse duration of the laser can be maintained and that the amplifier works without deteriorating the phase stability of the laser pulses, which is crucial for many modern applications such as high harmonic generation. The peak power behind the amplifier is high enough for white light generation in a bulk crystal at the full oscillator repetition rate of 80 MHz, which we demonstrate and which, to the best of our knowledge, has not been achieved before.
Wider implications. High harmonic generation allows the generation of frequency combs (Nobel Prize in physics in 2005) in the extreme ultraviolet (XUV). For versatile atomic spectroscopy of important systems like He+ it is of utmost interest to have high repetition rate XUV frequency combs available. The current amplifier will help to obtain high enough pulse energies for high harmonic generation at high repetition rates, particularly when combined with field enhancing methods such as a passive enhancement cavity.