Umeå University's logo

Optical parametric chirped-pulse amplification (OPCPA) is a light amplification technique that provides the combination of broad spectral gain bandwidth and large energy, directly supporting few-cycle pulses with multi-terawatt (TW) peak powers. Saturation in an OPCPA increases the stability and conversion efficiency of the system. However, distinct spectral components experience different gain and do not saturate under the same conditions, which reduces performance. Here, we describe a simple and robust approach to control the saturation for all spectral components. The demonstrated optimal saturation increases the overall gain, conversion efficiency and spectral bandwidth. We experimentally obtain an improvement of the pulse energy by more than 18%. This technique is easily implemented in any existing OPCPA system with a pulse shaper to maximize its output.

When a pulsed, few-cycle electromagnetic wave is focused by optics with f-number smaller than two, the frequency components it contains are focused to different regions of space, building up a complex electromagnetic field structure. Accurate numerical computation of this structure is essential for many applications such as the analysis, diagnostics, and control of high-intensity laser-matter interactions. However, straightforward use of finite-difference methods can impose unacceptably high demands on computational resources, owing to the necessity of resolving far-field and near-field zones at sufficiently high resolution to overcome numerical dispersion effects. Here, we present a procedure for fast computation of tight focusing by mapping a spherically curved far-field region to periodic space, where the field can be advanced by a dispersion-free spectral solver. In many cases of interest, the mapping reduces both run time and memory requirements by a factor of order 10, making it possible to carry out simulations on a desktop machine or a single node of a supercomputer. We provide an open-source C++ implementation with Python bindings and demonstrate its use for a desktop machine, where the routine provides the opportunity to use the resolution sufficient for handling the pulses with spectra spanning over several octaves. The described approach can facilitate the stability analysis of theoretical proposals, the studies based on statistical inferences, as well as the overall development and analysis of experiments with tightly-focused short laser pulses.

Temporal-intensity contrast is crucial in intense laser-matter interaction to circumvent the undesirable expansion of steep high-density plasma prior to the interaction with the main pulse. Nonlinear elliptical polarization rotation in an argon filled hollow-core fiber is used here for cleaning pedestals/satellite pulses of a chirped-pulse-amplifier based Ti: Sapphire laser. This source provides similar to 35 mu J energy and sub-4-fs duration, and the process has >50% internal efficiency, more than the most commonly used pulse cleaning methods. Further, the contrast is improved by 3 orders of magnitude when measured after amplifying the pulses to 16 TW using non-collinear optical parametric chirped pulse amplification with a prospect to even further enhancement.

The Fourier-transform limit achieved by a linear spectral phase is the typical optimum by the generation of ultrashort light pulses. It provides the highest possible intensity, however, not the shortest full width at half maximum of the pulse duration, which is relevant for many experiments. The approach for achieving shorter pulses than the original Fourier limit is termed temporal superresolution. We demonstrate this approach by shaping the spectral phase of light from an optical parametric chirped pulse amplifier and generate sub-Fourier limited pulses. We also realize it in a simpler way by controlling only the amplitude of the spectrum, producing a shorter Fourier-limited duration. Furthermore, we apply this technique to an optical parametric synthesizer and generate multi-TW sub-4-fs light pulses. This light source is a promising tool for generating intense and isolated attosecond light and electron pulses.

We report on details of a peak-power upgrade of a sub-5-fs Optical Parametric Synthesizer towards 100TW. System design, pump pulse delaying and relay imaging system arepresented. A tailored second and third harmonic generation reaches conversion efficiencies of 80% and 60% with 80ps pump pulses.

Optical parametric chirped-pulse amplification (OPCPA) [1] is an established light amplification technique with many beneficial properties, like high single pass gain, scalability, large spectral bandwidth, tunability and good conversion efficiency. Different methods have been proposed for optimization of conversion [2] - [4] mainly altering the pump or the crystal properties. However, seed manipulation to increase the OPCPA conversion efficiency has been only described in a general spatiotemporal field optimization theory so far [5]. Here, we show numerical and experimental results of a novel method to improve the gain saturation in an ultra-broadband OPCPA, hence conversion efficiency, by applying an adaptive spectral filter function to the seed pulses.

Optimization and simulation of non-collinear ultra-broadband optical parametric chirped pulse amplification setups rely on exact knowledge of the phase matching conditions. We present a method for their accurate retrieval by deterministic angular jitter and Monte-Carlo simulations.