Marco Hornung

Terawatt diode-pumped Yb:CaF2 laser

We present what we believe to be the first terawatt diode-pumped laser employing single-crystalline Yb:CaF(2) as the amplifying medium. A maximum pulse energy of 420 mJ at a repetition rate of 1 Hz was achieved by seeding with a stretched femtosecond pulse 2 ns in duration, preamplified to 40 mJ. After recompression, a pulse energy of 197 mJ and a duration of 192 fs were obtained, corresponding to a peak power of 1 TW. Furthermore, nanosecond pulses containing an energy of up to 905 mJ were generated without optical damage.

High-intensity, high-contrast laser pulses generated from the fully diode-pumped Yb:glass laser system POLARIS

We report on the first generation of high-contrast, 164 fs duration pulses from the laser system POLARIS reaching focused peak intensities in excess of 2×10(20) W/cm2. To our knowledge, this is the highest peak intensity reported so far that has been achieved with a diode-pumped, solid-state laser. Several passive contrast enhancement techniques have been specially developed and implemented, achieving a relative prepulse intensity smaller than 10(-8) at t=-30 ps before the main pulse. Furthermore a closed-loop adaptive-optics system has been installed. Together with angular chirp compensation, this method has led to a significant reduction of the focal spot size and an increase of the peak intensity.

16.6 J chirped femtosecond laser pulses from a diode-pumped Yb:CaF2 amplifier.

We report the amplification of laser pulses at a center wavelength of 1034 nm to an energy of 16.6 J from a fully diode-pumped amplifier using Yb:CaF2 as the active medium. Pumped by a total optical power of 300 kW from high-power laser diodes, a gain factor of g=6.1 was achieved in a nine-pass amplifier configuration agreeing with numerical simulations. A measured spectral bandwidth of 10 nm full width at half-maximum promises a bandwidth-limited compression of the pulses down to a duration of 150 fs. These are, to our knowledge, the most energetic laser pulses achieved from a diode-pumped chirped-pulse amplifier so far.

Alignment of a tiled-grating compressor in a high-power chirped-pulse amplification laser system

We present a novel technique to align a tiled grating in all five relevant degrees of freedom utilized in the compressor of the high-power chirped-pulse amplification laser system POLARIS at the Institute for Optics and Quantum Electronics, Jena, Germany. With this technique, alignment errors of the two gratings with respect to each other can be detected with an accuracy of 1 microrad for the rotational and 40 nm for the translational degrees of freedom. This is well sufficient to recompress 1030 nm pulses, which were stretched to 2.2 ns before amplification, to their bandwith limit of 150 fs.

All-reflective, highly accurate polarization rotator for high-power short-pulse laser systems

We present the setup of a polarization rotating device and its adaption for high-power short-pulse laser systems. Compared to conventional halfwave plates, the all-reflective principle using three zero-phase shift mirrors provides a higher accuracy and a higher damage threshold. Since plan-parallel plates, e.g. these halfwave plates, generate postpulses, which could lead to the generation of prepulses during the subsequent laser chain, the presented device avoids parasitic pulses and is therefore the preferable alternative for high-contrast applications. Moreover the device is easily scalable for large beam diameters and its spectral reflectivity can be adjusted by an appropriate mirror coating to be well suited for ultra-short laser pulses.

Spectrally resolved and phase-sensitive far-field measurement for the coherent addition of laser pulses in a tiled grating compressor

We describe a method that can be used for the coherent addition of laser pulses. As different laser pulses are initially generated in a laser-pulse compressor equipped with a tiled grating, such a coherent addition is indispensable in order to maximize the intensity in the laser far field. We present measurements in this context where, up to now, an unavoidable difference in the grating constants between the phased gratings reduced the maximum achievable intensity. The method significantly facilitates the high-precision alignment of a tiled grating compressor and could also be used for a coherent addition of laser pulses.

Full characterization of the amplified spontaneous emission from a diode-pumped high-power laser system

We present the first complete temporal and spatial characterization of the amplified spontaneous emission (ASE) of laser radiation generated by a diode-pumped high-power laser system. The ASE of the different amplifiers was measured independently from the main pulse and was characterized within a time window of -10ms ≤ t ≤ 10ms and an accuracy of up to 15fs around the main pulse. Furthermore, the focusability and the energy of the ASE from each amplifier was measured after recompression. Using our analysis method, the laser components, which need to be optimized for a further improvement of the laser contrast, can be identified. This will be essential for laser-matter interaction experiments requiring a minimized ASE intensity or fluence.

Ultra-high contrast frontend for high peak power fs-lasers at 1030 nm

We present the results from a new frontend within a double-chirped pulse amplification architecture (DCPA) utilizing crossed-polarized wave generation (XPW) for generating ultra-high contrast, 150 μJ-level, femtosecond seed pulses at 1030 nm. These pulses are used in the high energy class diode-pumped laser system Polaris at the Helmholtz Institute in Jena. Within this frontend, laser pulses from a 75 MHz oscillator-pulse train are extracted at a repetition rate of 1 Hz, temporally stretched, amplified and then recompressed reaching a pulse energy of 2 mJ, a bandwidth of 12 nm and 112 fs pulse duration at a center wavelength of 1030 nm. These pulses are temporally filtered via XPW in a holographic-cut BaF₂ crystal, resulting in 150 μJ pulse energy with an efficiency of 13 %. Due to this non-linear filtering, the relative intensity of the amplified spontaneous emission preceding the main pulse is suppressed to 2×10⁻¹³. This is, to the best of our knowledge, the lowest value achieved in a high peak power laser system operating at 1030 nm center wavelength.

The generation of amplified spontaneous emission in high‐power CPA laser systems

Abstract An analytical model is presented describing the temporal intensity contrast determined by amplified spontaneous emission in high‐intensity laser systems which are based on the principle of chirped pulse amplification. The model describes both the generation and the amplification of the amplified spontaneous emission for each type of laser amplifier. This model is applied to different solid state laser materials which can support the amplification of pulse durations ≤350 fs . The results are compared to intensity and fluence thresholds, e.g. determined by damage thresholds of a certain target material to be used in high‐intensity applications. This allows determining if additional means for contrast improvement, e.g. plasma mirrors, are required for a certain type of laser system and application. Using this model, the requirements for an optimized high‐contrast front‐end design are derived regarding the necessary contrast improvement and the amplified “clean” output energy for a desired focussed peak intensity. Finally, the model is compared to measurements at three different high‐intensity laser systems based on Ti:Sapphire and Yb:glass. These measurements show an excellent agreement with the model.

High contrast, 86 fs, 35 mJ pulses from a diode-pumped, Yb:glass, double-chirped-pulse amplification laser system.

We demonstrate the generation of 86 fs, 35 mJ, high-contrast laser pulses at 1030 nm with a repetition rate of 1 Hz from a diode-pumped double chirped-pulse amplification setup. The pulses exhibit a spectral bandwidth exceeding 27 nm full width at half-maximum. This could be achieved by using a laser architecture comprising two stages of chirped pulse amplification with a cross-polarized wave generation filter in between, by applying spectral shaping and by increasing the spectral hard-clip of the second stretcher. These are, to the best of our knowledge, the shortest pulses at the mJ level with ultra-high contrast generated with a diode-pumped front end at 1030 nm.