Optical parametric multi-pass cell amplifier

Abstract

Ultrafast lasers with simultaneously high average and peak power have become indispensable for driving a multitude of applications, including high-harmonic generation, strong-field physics, and particle source applications. Both parametric amplifiers and post-compressed Ytterbium lasers have emerged as prime platforms to meet these demands. While multi-pass cell (MPC) based post-compression offers broadband output with high beam quality, it provides limited wavelength tunability and suffers from temporal contrast degradation. Conversely, optical parametric amplifiers (OPAs) provide spectral tunability and high temporal contrast but they are limited by low pump-to-signal conversion efficiency and spatial beam inhomogeneities. Here, we introduce the Optical Parametric Multi-Pass Cell Amplifier (OPMPC), a hybrid architecture that overcomes the limitations of both schemes. Our approach utilizes two non-collinearly intersecting MPCs providing broadband parametric amplification of the seed pulses and complete idler removal after each pass through the crystal, thereby suppressing back-conversion. We experimentally demonstrate a record pump-to-signal power conversion efficiency of 43% using a 1030 nm pump at a 1 kHz repetition rate with a pulse energy of 174 $μ$J. The amplified signal at 1500 nm exhibits excellent beam quality, power and spectral stability and is compressed to 48 fs, demonstrating a new platform for ultrafast pulse generation.

Figures (7)

• Figure 1: Conceptualization of the OPMPC scheme, based on the combination of optical parametric amplification (OPA) and multi-pass cell (MPC) approaches, combining the respective advantages of both schemes. In the OPMPC, pump and seed beam co-propagate within the MPC passing a nonlinear crystal placed at the focus. The generated idler is ejected after each crystal pass e.g. via using a suitable mirror coating. After amplification, the signal beam is separated and compressed utilizing chirped mirrors (CM). Here, $\chi^{2}$ and $\chi^{3}$ represent the second-order and third-order nonlinear susceptibilities, respectively.
• Figure 2: Schematic of the experimental setup with the top and side view of the OPMPC scheme (WLG: White light generation, MMT: Mode-matching telescope, CM: Chirped mirrors).
• Figure 3: (a) Simulated (Sim.) and experimentally measured (Exp.) depletion of the pump, and conversion efficiency from the pump to the signal beam as a function of the number of passes in the OPMPC. We also display the optimized simulations (Opt.sim.) results for the maximum conversion efficiency reached with the theoretical d$_\textrm{eff}$, of 2 pm/V for KTA. (b) Experimentally measured amplified spectrum after each pass through the OPMPC with the colorbar indicating the number of passes. The gray shaded area shows the input seed spectrum magnified for visualization alongside the simulated amplified signal spectrum corresponding to the simulated (Sim.) conversion efficiency plot in (a). (c) Beam quality measurement of the signal output yielding an $M^2$ value of $1.29\times1.01$. The simulated and measured signal beam profile are shown as insets.
• Figure 4: (a) Spectrally resolved beam profile measurement along the (a) x-axis and (b) y-axis, and the corresponding spectral overlap parameter $V$ in (c) and (d), respectively. The areas where the intensity is lower than $1/e^2$ of the maximum are shaded in gray.
• Figure 5: (a) Simulated and measured compressed temporal output pulse profile retrieved from the FROG traces along with the FTL pulse. (b) Simulated spectrum, retrieved spectrum and spectral phase along with the measured spectrum. Measured (c) and retrieved (d) FROG traces of the compressed signal output.