Ultra-high-contrast few-cycle pulses for multipetawatt-class laser technology
Published in Optics Letters, Vol. 36 Issue 16, pp.3145-3147 (2011)
Spotlight summary: Since the technique of chirped pulse amplification (CPA) was first introduced by D. Strickland and G. Mourou in 1985, ultraintense and ultrashort pulse laser systems have been rapidly developed in the past few decades and now lead to a study of light matter interactions even in the relativistic regime at small-scale laboratories. To perform well-controlled light¬matter interaction experiments in such a high-intensity regime, the few cycle durations and the temporal contrast of the laser pulse are critical to achieve the high peak power and to rule out unwanted effects resulting from the temporal structure of laser pulses, respectively. However, CPA processes usually generate a large amount of amplified spontaneous emission nanosecond background, sub 100-ps time scale temporal structures and prepulses, significantly degrading temporal contrast of the laser pulse. For improving temporal contrast, a number of techniques have been suggested such as frequency doubling, plasma mirrors (PMs), saturable absorbers, optical parametric chirped pulse amplification (OPCPA), and cross-polarized wave generation (XPW).
In a paper by Mikhailova et al., the authors construct a state-of-the-art laser system that generates few cycle multiterawatt pulses with a temporal contrast of greater than 1010 by integrating two pulse cleaning techniques, XPW and PM, into the OPCPA system. A brief description of the authors' laser system is as follows: Femtosecond pulses from a Ti:sapphire oscillator are first amplified using a multipass Ti:sapphire amplifier and then are spectrally broadened in the wavelength range of 700-1000 nm in a neon-filled, hollow-core fiber (HCF) for the generation of few cycle pulses. Improving the temporal contrast of fs laser pulses by a XPW unit using a third-order nonlinear process in BaF2 follows the spectral broadening process in an HCF. Subsequently, the pulses are stretched by a negative-grism stretcher and acousto-optical modulator and then are amplified parametrically over a broad spectral band with greatly reduced background radiation in two noncollinear OPCPA stages. Once the broadband parametric amplification is finished in two OPCPA stages, a positive-dispersion, bulk-glass precompressor and four chirped multilayer mirrors in a vacuum chamber recompress the stretched pulses. Finally, a PM is used to further enhance the temporal contrast of the recompressed pulses, since it can eliminate low-intensity background prior to the formation of plasma induced by the primary pulse, without affecting the FWHM pulse duration.
Overall, the authors demonstrate the generation of ultrahigh contrast few cycle multiterawatt pulses with a pulse duration and energy of 7.8 fs and 100 mJ, respectively, using a combination of XPW, PM, and two OPCPA stages. As the authors note, these pulses themselves allow for a new class of high-field experiments and moreover can be used for a light source for a high-contrast multipetawatt laser system.
--Taek Yong Hwang
Technical Division: Optoelectronics
ToC Category: Lasers and Laser Optics
|OCIS Codes:||(140.7090) Lasers and laser optics : Ultrafast lasers|
|(190.4970) Nonlinear optics : Parametric oscillators and amplifiers|
|(320.7090) Ultrafast optics : Ultrafast lasers|
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