Abstract

In the past several years, a new class of ultrashort pulse sources for long-wavelength-driven strong-field experiments has been developed based on ultrabroadband optical parametric chirped pulse amplification (OPCPA) with 2-μm signal wavelength [1-3]. These amplifiers share the advantageous properties of few-cycle duration, passive carrier-envelope phase control and close-to-millijoule energy, but also, due to low seed energy, high gain, and large mode cross section, a propensity towards significant contamination from amplified vacuum noise. This amplified superfluorescence has been found both to degrade the signal-to-noise ratio (SNR) and to transfer a significant portion of the pump wave energy to an incoherent pedestal remaining after compression. The ratio of coherent amplified signal energy and incoherent superfluorescence pedestal energy, i.e., signal-to-pedestal ratio (SPR), has been measured as low as 4:1 [2], and its degradation remains a limitation to pulse energy scalability. Due to the intrinsic difficulty of their experimental measurement and the nonlinear and quantum-mechanical nature of the physical system, the saturation dynamics of quantum noise in OPCPA have remained controversial. Their understanding, however, is requisite for optimization of OPCPA performance.

© 2011 Optical Society of America