Spectral broadening in convex-concave multipass cells.

Since its first demonstration in 2016, the multi-pass spectral broadening technique has covered impressive ranges of pulse energy (3 µJ - 100 mJ) and peak power (4 MW - 100 GW). Energy scaling of this technique into the joule-level is currently limited by phenomena such as optical damage, gas ionization and spatio-spectral beam inhomogeneity. These limitations can be overcome by the novel multi-pass convex-concave arrangement, which exhibits crucial properties such as large mode size and compactness. In a proof-of-principle experiment, 260 fs, 15 µJ and 200 µJ pulses are broadened and subsequently compressed to approximately 50 fs with 90% efficiency and excellent spatio-spectral homogeneity across the beam profile. We simulate the proposed concept for spectral broadening of 40 mJ and 1.3 ps input pulses and discuss the possibility of further scaling.

Multipass spectral broadening and compression in the green spectral range.

Multipass spectral broadening and compression around 515 nm are experimentally demonstrated. A nonlinear multipass cell with a bulk medium is used to compress 250-fs pulses down to 38 fs. The same input pulses create a sufficient bandwidth for sub-20-fs pulse generation in a multipass cell with gaseous media. In both cases, the efficiency exceeds 85%. Dispersion management by reduction of the cell size and the thickness of the nonlinear medium allows an efficient generation of ultrashort pulses in the visible range and establishes a pathway for ultraviolet spectral broadening by means of multipass cells.

Direct refractive index retrieval from interferometry measurements.

We present an alternative numerical method to the Abel inversion technique, which can be applied to complex non-symmetrical systems. A comparison with the Abel inversion algorithm was conducted. For benchmarking, the method was applied to a synthetic trace representing a plasma waveguide characterized by a constant parabolic density profile. Furthermore, the temperature and refractive index of a plume of hot air surrounding a non-cylindrical soldering iron were retrieved. Temperatures between 50 °C and 200 °C were successfully retrieved within the instrument precision. The proposed method allows robust and fast data retrieval while maintaining the accuracy and resolution of well-known methods, as Abel inversion.

Pulse front tilt control using non-collimated beams in a single pass grating compressor.

High power laser systems based on the chirped pulse amplification (CPA) technique make use of grating pairs to compress the pulse to a short duration. When designing the pulse compressor, it is normally assumed that good beam collimation is a strong requirement in order to avoid spatio-temporal couplings. We analyze the propagation through a single pass compressor without the good collimation approximation and show that this results in a compressed pulse exhibiting pulse front tilt, whose magnitude is proportional to the normalized distance to the beam waist, providing a simple mechanism for controlling the tilt angle. We perform experimental measurements in a large-scale CPA laser for a range of beam curvatures that confirm these results.

Increased bandwidth optical parametric amplification of supercontinuum pulses with angular dispersion.

The use of a controlled, removable angular dispersion applied to the signal beam in a plane orthogonal to that containing the noncollinear angle is experimentally demonstrated as a technique to broaden the gain bandwidth in optical parametric chirped-pulse amplification. With a pump beam centered at 526 nm the supercontinuum signal is amplified in the 900 to 1220 nm range in a beta-barium borate crystal with a gain >1000. This represents a bandwidth improvement greater than 30% relative to conventional designs.

Single adjuster deformable mirror with four contact points for simultaneous correction of astigmatism and defocus.

We show that a deformable mirror with four point actuators is suitable for the simultaneous correction of astigmatism and defocus in a given optical system by adequately choosing the relative position of the actuators. An analytical model is developed that describes adequately the mirror deformation as a function of actuator position, showing that it is possible to continuously tune the weight of each aberration. Experimental measurements with a single adjuster deformable mirror assembly confirm the validity of the model.

Self-referencing spectral phase interferometry for direct electric-field reconstruction with chirped pulses.

We analyze the characterization of strongly chirped pulses by spectral phase interferometry for direct electric-field reconstruction (SPIDER). We show how to extend the working range of this technique for these relevant cases and derive correction factors for typical operating parameters. The results are straightforward to implement in the calculation algorithms. We demonstrate the validity of this technique by characterizing numerically and experimentally pulses with a known spectral phase profile.

Bandwidth increase by controlled angular dispersion of signal beam in optical parametric amplification.

Angular dispersion of the signal beam inside the nonlinear media is introduced to improve the non-collinear phase-matching range. Simulations run for BBO crystals predict that bandwidth increase is possible for most of the application spectral range and that it can surpass one order of magnitude in some particular configurations.