Nonlinear compression of few-cycle multi-mJ 5 µm pulses in ZnSe around zero-dispersion.

We present a compact nonlinear compression scheme for the generation of millijoule few-cycle pulses beyond 4 µm wavelength. For this purpose 95 fs pulses at 5 µm from a 1 kHz midwave-IR optical parametric chirped pulse amplifier (OPCPA) are spectrally broadened due to a self-phase modulation in ZnSe. The subsequent compression in a bulk material yields 53 fs pulses with 1.9 mJ energy. The compression succeeds efficiently with only slight beam distortions and an energy throughput of 85%, which results in a peak power of 34 GW. The nonlinear refractive index of ZnSe was derived from the nonlinear compression and self-focusing measurements. Furthermore, we explore to which extent multiphoton absorption affects the nonlinear compression regime.

Pulse shaping in a midwave-IR OPCPA for multi-µJ few-cycle pulse generation at 12 µm via DFG.

We report on dispersion management in mid-IR optical parametric chirped pulse amplifiers (OPCPA) aiming for high-energy few-cycle pulses beyond 4 µm. The available pulse shapers in this spectral region limit the feasibility of sufficient higher-order phase control. Intending the generation of high energy pulses at 12 µm via DFG driven by the signal and idler pulses of a midwave-IR OPCPA, we introduce alternative approaches for mid-IR pulse shaping, namely a germanium-prism pair and a sapphire-prism Martinez compressor. Furthermore, we explore the limits of bulk compression in Si and Ge for multi-mJ pulse energies.

10-µJ few-cycle 12-µm source based on difference-frequency generation driven by a 1-kHz mid-wave infrared OPCPA.

We report on high-energy, few-cycle pulse generation in the long-wave infrared spectral region via difference-frequency generation (DFG) in GaSe and AgGaSe2 nonlinear crystals. The DFG is driven by the signal at 3.5 µm and idler at 5 µm of a high-power mid-wave infrared optical parametric chirped pulse amplification (OPCPA) system operating at a 1-kHz repetition rate. The DFG pulses contain up to 17 µJ of energy and cover a spectrum from 8.5 µm to 14.5 µm. They are generated with a conversion efficiency of 2.1 %. Compression results in 10.2-µJ pulses with sub-150-fs duration, corresponding to less than four optical cycles.

Femtosecond multi-10-mJ pulses at 2 µm wavelength by compression in a hollow-core fiber.

High-energy few-ps pulses from a Ho:YLF chirped pulse amplifier operating at a 1 kHz repetition rate are compressed in a two-stage arrangement to sub-90-fs duration. The energy of the compressed pulses is more than 20 mJ at an average power of 20 W. In the first stage, the duration of the 2.8 ps, 40 mJ pulses at 2.05 µm wavelength was reduced to 1.4 ps by using nonlinear propagation in air. Subsequently, the pulses were further compressed to 86 fs after spectral broadening in a 3-m-long Kr-filled stretched flexible hollow-core fiber. The high photon flux, peak power, and excellent beam quality and stability make this light source highly attractive for fs pulse generation in the extreme ultraviolet (XUV) to x-ray spectral range for time-resolved XUV spectroscopy or measurements of structural dynamics in solids.

Compact OPCPA system seeded by a Cr:ZnS laser for generating tunable femtosecond pulses in the MWIR.

A compact mid-wavelength infrared (MWIR) optical parametric chirped pulse amplification (OPCPA) system generates sub-150 fs pulses at wavelengths from 5.4 to 6.8 µm with >400µJ energy at a 1 kHz repetition rate. A femtosecond Cr:ZnS master oscillator emitting 40 fs pulses at 2.4 µm seeds both a Ho:YLF regenerative amplifier and a two-stage OPCPA based on ZnGeP2 crystals. The 2.05 µm few-picosecond pump pulses from the Ho:YLF amplifier have an energy of 13.4 mJ. Seed pulses for the OPCPA are generated by soliton self-frequency shifting in a fluoride fiber and are tunable between 2.8 and 3.25 µm with a sub-100 fs duration and few-nanojoule energy. The intense MWIR pulses hold strong potential for applications in ultrafast mid-infrared nonlinear optics and spectroscopy.

Compact high-flux hard X-ray source driven by femtosecond mid-infrared pulses at a 1 kHz repetition rate.

A novel, to the best of our knowledge, table-top hard X-ray source driven by femtosecond mid-infrared pulses provides 8 keV pulses at a 1 kHz repetition rate with an unprecedented flux of up to 1.5×1012 X-ray photons/s. Sub-100 fs pulses at a center wavelength of 5 µm and multi-millijoule energy are generated in a four-stage optical parametric chirped-pulse amplifier and focused onto a thin Cu tape target. Electrons are extracted from the target and accelerated in a vacuum up to 100 keV kinetic energy during the optical cycle; the electrons generate a highly stable K α photon flux from the target in a transmission geometry.

Multi-millijoule, few-cycle 5 µm OPCPA at 1 kHz repetition rate.

A table-top midwave-infrared optical parametric chirped pulse amplification (OPCPA) system generates few-cycle pulses with multi-10 GW peak power at a 1 kHz repetition rate. The all-optically synchronized system utilizes ZnGeP2 nonlinear crystals and a highly stable 2 µm picosecond pump laser based on Ho:YLiF4. An excellent energy extraction is achieved by reusing the pump pulse after the third parametric power amplification stage, resulting in 3.4 mJ idler pulses at a center wavelength of 4.9 µm. Pulses as short as 89.4 fs are achieved, close to only five optical cycles. Taking into account the pulse energy, a record high peak power of 33 GW for high-energy mid-IR OPCPAs beyond 4 µm wavelength is demonstrated.

2.05 µm chirped pulse amplification system at a 1 kHz repetition rate-2.4 ps pulses with 17 GW peak power.

Ho-doped yttrium lithium fluoride chirped pulse amplification (CPA) is implemented with a high-gain regenerative amplifier (RA) and a two-stage booster amplifier. We demonstrate the generation of 52.5 mJ pulses with a duration of 2.4 ps at a 1 kHz repetition rate. A peak power of 17 GW is achieved for the 2050 nm pulses. The CPA displays a remarkably high stability with a pulse-to-pulse rms as low as 0.23%. The RA operates without any signs of bifurcation and delivers 12 mJ pulses. Seeding the booster amplifier with the RA output scales the pulse energy linearly up into the 50-60 mJ range. The amplifier system is operated at room temperature and shows a high optical-to-optical efficiency of 20.3% with respect to the optical pump power.

5 µm few-cycle pulses with multi-gigawatt peak power at a 1 kHz repetition rate.

A mid-infrared (mid-IR) optical parametric chirped pulse amplification (OPCPA) system generating few-cycle pulses with multi-gigawatt peak power at a 1 kHz repetition rate is reported. The system is pumped by a highly stable 2 µm picosecond chirped pulse amplifier based on Ho:YLF gain media to exploit the high nonlinearity of ZnGeP2 (ZGP) crystals for parametric amplification. The ZGP optical parametric amplification (OPA) is characterized by a high conversion efficiency of >10 %, resulting in 1.3 mJ idler pulses at a center wavelength of 5.1 µm. Employing a dispersion management scheme based only on bulk materials, pulses as short as 160 fs are obtained. By adding a spatial light modulator in the OPCPA setup, the pulses are further recompressed to 75 fs duration which corresponds to less than five optical cycles. Taking into account the pulse energy of 0.65 mJ in this configuration, it translates into a peak power of 7.7 GW. The achieved pulse durations and peak powers, to the best of our knowledge, represent record values for high-energy mid-IR OPCPAs beyond 4 µm.

Picosecond 34 mJ pulses at kHz repetition rates from a Ho:YLF amplifier at 2 µm wavelength.

A 2.051-µm laser source delivering picosecond pulses with energies as high as 34 mJ at a 1 kHz repetition rate is reported. The main amplifier system is based on Ho:YLF and consists of a regenerative amplifier (RA) and a single-pass booster amplifier running at room temperature. The continuous-wave pumped, high-gain RA produces pulse trains with up to 10-mJ energy when operating in a stable periodic doubling regime. The recorded complete RA bifurcation diagram agrees well with our numerical simulations. At the highest pulse energy after the booster amplifier the pulse-to-pulse fluctuations are as low as 0.9% rms. Pulse compression is performed up to the 10-mJ level resulting in a duration of 37 ps.