# Towards high power broad-band OPCPA at 3000 nm

## TL;DR

This paper demonstrates a four-stage optical parametric chirped pulse amplifier (OPCPA) producing high-energy, broadband, 3000 nm pulses with 65 fs duration, suitable for high-power, high-repetition-rate applications in the mid-infrared.

## Contribution

The paper presents a novel four-stage OPCPA architecture achieving high-energy, broadband 3000 nm pulses with efficient conversion and compression, advancing mid-infrared ultrafast laser technology.

## Key findings

- Generated 430 μJ pulses at 3000 nm with 490 nm bandwidth.
- Achieved pulse compression to 65 fs duration.
- Operates near optimal efficiency with minimal absorption losses.

## Abstract

High-energy femtosecond laser pulses in the mid-infrared (MIR) wavelength range are essential for a wide range of applications from strong-field physics to selectively pump and probe low energy excitations in condensed matter and molecular vibrations. Here we report a four stage optical parametric chirped pulse amplifier (OPCPA) which generates ultrashort pulses at a central wavelength of 3000 nm with 430 $\mu$J energy per pulse at a bandwidth of 490 nm. Broadband emission of a Ti:sapphire oscillator seeds synchronously the four OPCPA stages at 800 nm and the pump line at 1030 nm. The first stage amplifies the 800 nm pulses in BBO using a non-collinear configuration. The second stage converts the wavelength to 1560 nm using difference frequency generation in BBO in a collinear geometry. The third stage amplifies this idler frequency non-collinearly in KTA. Finally, the fourth stage generates the 3000 nm radiation in a collinear configuration in LiIO$_3$ due the broad amplification bandwidth this crystal provides. We compress these pulses to 65 fs by transmission through sapphire. Quantitative calculations of the individual non-linear processes in all stages verify that our OPCPA architecture operates close to optimum efficiency at minimum absorption losses, which suggests that this particular design is very suitable for operation a high average power at multi kHz repetition rates.