In-line synthesis of multi-octave phase-stable infrared light.

Parametric downconversion driven by modern, high-power sources of 10-fs-scale near-infrared pulses, in particular intrapulse difference-frequency generation (IPDFG), affords combinations of properties desirable for molecular vibrational spectroscopy in the mid-infrared range: broad spectral coverage, high brilliance, and spatial and temporal coherence. Yet, unifying these in a robust and compact radiation source has remained a key challenge. Here, we address this need by employing IPDFG in a multi-crystal in-line geometry, driven by the 100-W-level, 10.6-fs pulses of a 10.6-MHz-repetition-rate, nonlinearly post-compressed Yb:YAG thin-disk oscillator. Polarization tailoring of the driving pulses using a bichromatic waveplate is followed by a sequence of two crystals, LiIO3 and LiGaS2, resulting in the simultaneous coverage of the 800-cm-1-to-3000-cm-1 spectral range (at -30-dB intensity) with 130 mW of average power. We demonstrate that optical-phase coherence is maintained in this in-line geometry, in theory and experiment, the latter employing ultra-broadband electro-optic sampling. These results pave the way toward coherent spectroscopy schemes like field-resolved and frequency-comb spectroscopy, as well as nonlinear, ultrafast spectroscopy and optical-waveform synthesis across the entire infrared molecular fingerprint region.

Efficient nonlinear compression of a thin-disk oscillator to 8.5 fs at 55 W average power.

We demonstrate an efficient hybrid-scheme for nonlinear pulse compression of high-power thin-disk oscillator pulses to the sub-10 fs regime. The output of a home-built, 16 MHz, 84 W, 220 fs Yb:YAG thin-disk oscillator at 1030 nm is first compressed to 17 fs in two nonlinear multipass cells. In a third stage, based on multiple thin sapphire plates, further compression to 8.5 fs with 55 W output power and an overall optical efficiency of 65% is achieved. Ultrabroadband mid-infrared pulses covering the spectral range 2.4-8µm were generated from these compressed pulses by intra-pulse difference frequency generation.

Directly diode-pumped, Kerr-lens mode-locked, few-cycle Cr:ZnSe oscillator.

Lasers based on Cr2+-doped II-VI material, often known as the Ti:Sapphire of the mid-infrared, can directly provide few-cycle pulses with octave-spanning spectra, and serve as efficient drivers for generating broadband mid-infrared radiation. It is expected that the wider adoption of this technology benefits from more compact and cost-effective embodiments. Here, we report the first directly diode-pumped, Kerr-lens mode-locked Cr2+-doped II-VI oscillator pumped by a single InP diode, providing average powers over 500 mW and pulse durations of 45 fs - shorter than six optical cycles at 2.4 µm. These correspond to a sixty-fold increase in peak power compared to the previous diode-pumped record, and are at similar levels with respect to more mature fiber-pumped oscillators. The diode-pumped femtosecond oscillator presented here constitutes a key step toward a more accessible alternative to synchrotron-like infrared radiation and is expected to accelerate research in laser spectroscopy and ultrafast infrared optics.

Kerr-lens mode-locked thin-disk oscillator with 50% output coupling rate.

Several approaches to power scaling of mode-locked thin-disk oscillators exist. One of these approaches is based on the increased gain provided by multiple passes through the thin-disk laser medium. For the first time, to the best of our knowledge, we applied this approach to a Kerr-lens mode-locked thin-disk oscillator. The so obtained additional gain allowed mode-locked operation with up to 50% output coupling rate. This first demonstration is of particular importance for gain media with inherently low-emission cross sections and paves the way to even more powerful Kerr-lens mode-locked thin-disk oscillators. Moreover, the experimental results indicate an increased self-amplitude modulation related to an overall increase in the soft-aperture Kerr-lens effect.