Edgar Kaksis

110-mJ 225-fs cryogenically cooled Yb:CaF 2 multipass amplifier.

We report on a diode-pumped cryogenically cooled bulk Yb:CaF2 12-pass amplifier delivering 110-mJ, 1030-nm pulses at a 50-Hz repetition rate. The pulses have a spectral bandwidth of 13 nm and are compressed to 225 fs pulse duration in a double reflection grating based compressor having a transmission efficiency of >90%. The measured output beam quality is M2<1.1. A key feature of the amplifier design is the 4f relay imaging onto the gain medium with progressive beam magnification for the mitigation of the spatial gain narrowing effect. The number of passes in the amplifier is scalable by increasing the size of imaging mirrors. In order to prevent accumulation of nonlinear phase due to self-phase modulation in air, the amplifier is enclosed into a low-vacuum case.

High-energy pulse stacking via regenerative pulse-burst amplification

Here we present a coherent pulse stacking approach for upscaling the energy of a solid-state femtosecond chirped pulse amplifier. We demonstrate pulse splitting into four replicas, amplification in a burst-mode regenerative Yb:CaF2 amplifier, designed to overcome intracavity optical damage by colliding pulse replicas, and coherent combining into a single millijoule level pulse. The thresholds of pulse-burst-induced damage of optical elements are experimentally investigated. The scheme allows achieving an enhancement factor of 2.62 using a single-stage stacker cavity and, potentially, much higher enhancement factors using cascaded stacking.

220-fs 110-mJ Yb:CaF2 cryogenic multipass amplifier

We report on the design and performance of a Yb:CaF2 booster with a pass-by-pass compensated spatial gain narrowing. A 5-concave-mirror design affords a flexible number of passes as well as 4f image relay and progressive beam magnification onto the laser crystal.

Multi-millijoule Few-Optical-Cycle Pulses in Mid-IR: Scaling Power, Energy and Wavelength

We discuss prospects of the generation of high power mid-IR pulses by analyzing soliton self-compression of multi-mJ 4-μm pulses and the development of few-optical-cycle 6-μm optical parametric amplifier. Scalability of pump lasers is addressed.

Generation of a single UV pulse from a near-IR pulse burst

High harmonic generation (HHG) requires high peak-power laser sources. Most of the well-known high peak power lasers are operating in the near-IR wavelength region. Recently it was demonstrated that HHG can be effectively phase matched in the soft X-ray region by using very high intensity UV lasers and multiply charged ions [1]. High average and high peak power UV sources operating around and below 280 nm are required for many other applications, such as ablation in ophthalmology, materials processing and photoelectron spectroscopy. Due to lack of ultrafast high peak power lasers operating in UV, generation of ultrashort UV pulses is possible by up-converting frequency of near-IR laser. This can be done by cascaded harmonic generation in nonlinear crystals with efficiency higher than 40% [2]. However, to obtain high pulse energies in UV region, high energy IR pump is necessary. This becomes increasingly difficult for femtosecond laser pulses because of the optical damage problem in CPA systems. Very high pulse stretching rates in the CPA become unfeasible due to the limited size of dispersive optics. Alternatively, the intensity in the laser cavity can be decreased by using a pulse burst which effectively increases the pulse duration. Therefore, this approach is also suitable for increasing energy throughput in fiber delivery and fiber post compression schemes [3].

High repetition rate fs pulse burst generation using the Vernier effect

We demonstrate pulse burst generation method based on the Vernier effect. The pulse burst with controllable amplitudes and phases is formed using a femtosecond oscillator and regenerative amplifier cavity that have slightly different round trip times. This operation mode can be used for the purposes of coherent pulse stacking, rapid material miroprocessing and rapid scan spectroscopy.

Development of a high-power mid-IR parametric amplifier for multicolor driving of high harmonic generation

We developed a multicolour, high-peak-power mid-IR parametric amplifier with the base period corresponding to 3.1 µm and a combined pulse energy >15 mJ, which is aimed at a “perfect wave” driver for high harmonic generation.

110-mJ Femtosecond Pulses at 50 Hz from a Cryogenic Multipass Yb:CaF2 Amplifier

110-mJ sub 200-fs pulses are generated at the repetition rate of 50 Hz in a cryogenically cooled multipass Yb:CaF2 amplifier. The amplifier output is scalable in both energy and repetition rate.