Spatio-spectral couplings in saturated collinear OPCPA.

Timo Eichner,Tino Lang,Lutz Winkelmann,Guido Palmer,Thomas Hülsenbusch,Andreas R Maier,Julian Dirkwinkel

doi:10.1364/oe.448551

Abstract

Ultrafast laser pulses featuring both high spatio-temporal beam quality and excellent energy stability are crucial for many applications. Here, we present a seed laser with high beam quality and energy stability, based on a collinear optical parametric chirped pulse amplification (OPCPA) stage, delivering 46 µJ pulses with a 25 fs Fourier limit at 1 kHz repetition rate. While saturation of the OPCPA stage is necessary for achieving the highest possible energy stability, it also leads to a degradation of the beam quality. Using simulations, we show that spectrally dependent, rotationally symmetric aberrations dominate the collinear OPCPA in saturation. We experimentally characterize these aberrations and then remove distinct spatial frequencies to greatly improve the spectral homogeneity of the beam quality, while keeping an excellent energy stability of 0.2 % rms measured over 70 hours.

Highlights

The combination of high spatio-temporal beam quality and high energy stability are essential for a variety of high-intensity laser applications ranging from ultrafast spectroscopy [1,2] and microscopy [3] to laser-plasma acceleration (LPA) [4,5]
We have presented a collinear optical parametric chirped pulse amplification (OPCPA) system dedicated to providing low-spatio-temporal coupling (STC) seed pulses with high energy stability to seed a high intensity laser amplification systems for laser-plasma acceleration
To reach this high energy stability, the amplification process had to be saturated, which leads to aberrations of the intensity profile and wavefront of the pulse

Summary

Introduction

The combination of high spatio-temporal beam quality and high energy stability are essential for a variety of high-intensity laser applications ranging from ultrafast spectroscopy [1,2] and microscopy [3] to laser-plasma acceleration (LPA) [4,5]. Optical parametric chirped pulse amplification (OPCPA) [14] is often used as an alternative to more conventional Ti:Sapphire based regenerative amplifiers that are commonly found in the low energy front-end of high intensity laser systems [15,16,17]. Thereby, higher pulse quality can be achieved without the complexity of additional preventive measures required by NOPAs. The trade-off is in the phase matching bandwidth, which is significantly lower in the collinear case, but still sufficient to provide pulse durations in the 15-20 fs range which is enough for seeding many high-energy Ti:Sapphire systems. We show that spatial filtering can greatly improve the uniformity of the beam quality across the spectrum of the amplified pulses

Experimental setup and laser performance

Simulation of beam quality in the saturation regime

Measurement of STCs and results

Findings

Conclusion