Temporal Characterization of Front-End for Yb-Based High-Energy Optical Waveform Synthesizers

Abstract

Abstract:We demonstrate temporal characterization of the front-end for an Yb-based, passively CEP-stable, two-octave-wide, two-channel optical parametric synthesizer driven by slightly subpicosecond pump pulses from a multi-mJ regenerative amplifier at 1 kHz.OCIS codes: (320.6629) Supercontinuum generation; (320.7110) Ultrafast nonlinear optics; (190.7110) Ultrafast nonlinear optics High-harmonic generation (HHG) is an established powerful method, which allows characterization of atomic or interatomic transitions below the femtosecond time scale in the extreme ultraviolet (XUV) and soft X-ray spectral regions. However, HHG is a very inefficient process to generate isolated attosecond pulses. Coherent optical pulse synthesis of high-energy, few-cycle pulses is one of the most promising methods to efficiently generate isolated attosecond pulses because of the flexibility in spectral shaping and scalability in spectral bandwidth as well as energy [1][2][3][4]. Since the HHG process is driven by the electric field E(t) of an optical pulse, control of the carrierenvelope phase (CEP) is crucial. The CEP can be controlled either actively [2], requiring several feedback loops increasing the system's complexity, or passively, using the difference-frequency process [3][4][5].Previously, we demonstrated passively CEP-stabilized synthesizers pumped by Ti:Sapphire laser technology [3,4], and we have been pursuing average-power scaling with Yb-based pump technology [6,7]. In this particular study, we demonstrate the temporal characterization of a two-channel parametric synthesizer at the µJ energy level, which will serve as the seed source for a mJ-level pulse synthesizer. The system comprises two-octave, passively CEP-stable, two-channel optical parametric amplifiers (OPAs) driven by sub-picosecond pulses [8] from an Ybbased multi-mJ regenerative amplifier. The OPAs are seeded by a passively CEP-stable front-end based on whitelight supercontinuum generation in bulk [9]. Fig. 1 shows the layout of the dual-channel OPA system driven by an Yb:KYW regenerative amplifier. The compressed output of the Yb:KYW regenerative amplifier delivering 4.2-mJ, 615-fs long pulses [3] is split between a front-end generating nJ-level, CEP-stable pulses with spectrum extending from the visible up to the Mid-IR, and the pumping of two 2-stage OPA channels in the Near and Mid-IR spectral regions. The CEP-stable front-end comprises 3 steps: a first white-light stage broadens the spectrum of the regenerative amplifier; 2 consecutive OPA stages amplify a narrow-band spectral region to the µJ level in the Mid-IR; the second harmonic of the resulting CEP-stable idler generates white-light in YAG, which is the seed of the following OPAs [3,4]. Fig. 1. Layout of the dual-channel OPA system driven by an Yb:KYW regenerative amplifier: the signal is generated in the CEP-stable white-light based front-end, and spectra after amplification and compression stages are shown.The Near-IR non-collinear OPA (NOPA) stages are pumped by the second harmonic of the rege...