Recently, we published a novel design approach for unstable laser cavities that overcomes the limitation of such a design to high gain media and presented first results of a laboratory prototype . Based on this, we developed a larger prototype system suitable for applications in laser shock peening featuring a relatively simple layout and a compact footprint of about 0.8x0.6m².
The presented laser is based on cryogenically cooled Yb:YAG ceramic equipped with a Cr:YAG absorber cladding to suppress amplified spontaneous emission. As the pump source we utilize a 7kW peak power laser diode module generating a high quality tophat beam with hexagonal lateral profile. With this the system achieves an output energy in excess of 1J in a 10ns to 20ns pulse in q-switch operation mode. The output beam profile adapts well to the hexagonal shape of the pump beam. The laser can be operated with up to 20Hz repetition rate limited only by the cooling capacity of the used cryostat.
The application of the system in laser shock peening (LSP) was tested by treating aluminum plates within a test setup. The treated area was then examined regarding residual stress to verify the success of the LSP process. It was found that significant residual stress was generated with a penetration depth of up to 0.6mm and a pressure of 200MPa at the surface.
 J. Körner, S. Zulić, D. Rostohar, A. Lucianetti, T. Mocek, “Novel unstable resonator configuration for highly efficient cryogenically cooled Yb: YAG Q-switched laser”, Optics Express, 27(15): 21622-21634, 2019
When applying picosecond laser pulses of the order of several mJ pulse energy, the goal is to deliver the pulses effectively to the surface. HiLASE have development novel diode pumped thin-disk laser systems which are used for high speed drilling (700 holes simultaneously) and high speed surface structuring (several cm2 per second). Different methods of multi-beam processing will be presented.
We present a novel approach to combine diode-pumped, moderately low-gain media with the advantages of an unstable cavity. To this end, we propose to utilize a spatially tailored gain profile in the active medium instead of using a graded reflectivity mirror to provide an eeffective shaping mechanism for the intra-cavity intensity distribution. The required gain profile can be easily generated with a state-of-the-art homogenized laser diode pump beam in an end-pumped configuration.
The “Bivoj” 10 J, 10 ns, 10 Hz, Yb:YAG (1030 nm) diode-pumped solid state laser (DPSSL) at the HiLASE Centre was used to investigate the laser-induced damage of optical glasses with different refractive index (BK7, SF8, FS, LIBA2000). The samples were polished using a combination of methods and cleaned in ultrasonic bath or with ion beams. Sample surface was characterized using white-light interferometry (WLI) and laser confocal microscopy (LCM). For the laser-induced damage threshold (LIDT), an S-on-1 procedure was selected, the testing taking place in accordance with the ISO 21254 standard. Due to the high energy per pulse of the “Bivoj” system we were capable of using beams with more than 500 μm diameter (using a long focusing mirror) and thus, including different surface defect in the LIDT measurement. The damage of the glasses was usually observed on the rear side (ballistic damage) due to constructive interference, however we manage to see on few samples front damage also. Values above 50 J/cm2 were common for all tested samples.
Yttrium aluminum garnet (YAG) crystals are one of the most important materials for active media in solid-state laser technology. Reach for higher energies brings more stress into crystals thin film coatings field, where methods used in the past are not sufficient anymore. Laser induced damage threshold (LIDT) became a major issue in further exploitation of YAG crystals as required extraction fluencies exceed tens J·cm-2 in nanosecond regime. Consequently, improved coating techniques based on e-beam deposition were introduced in order to improve damage resistance of active media. Thin films prepared on YAG crystals either by reactive or ion-assisted e-beam deposition technique were tested on LIDT by son- 1 method according to the ISO standards recommendations and results are presented in following paper.
Around BIVOJ laser system, a new generation diode pump solid state laser (10-100J energy in 2-10 ns pulses with 10 Hz repetition frequency at 1030 nm) recently was developed a LSP experimental station. In this paper status and further developments of LSP facility at HiLASE Centre as well as further BIVOJ laser upgrades are presented. Residual stress curves representing preliminary results on treating Aluminum 7075 alloy will be also reported.
Recent development of a station dedicated to Laser Shock Peening around newly developed BIVOJ laser system is reported. We also describe further plans related to upgrade of the laser system itself as well as plans for establishment of a dedicated sample preparation and characterization lab.
So-called hybrid mirrors, consisting of broadband metallic surface coated with dielectric reflector designed for specific
wavelength, becoming more important with progressing development of broadband mid-IR sources realized using
parametric down conversion system. Multiple pulse nanosecond laser induced damage on such mirrors was tested by
method s-on-1, where s stands for various numbers of pulses. We show difference in damage threshold between common
protected silver mirrors and hybrid silver mirrors prepared by PVD technique and their variants prepared by IAD.
Fused silica based optical fibers are broadly used for beam delivery in laser technology, mostly for continuous lasers. However, powerful pulsed beams are still very challenging for optical fiber technology; in particular in the field of pulsed lasers providing ns-length pulses or shorter at high repetition rate. According to the current knowledge, laser induced damage threshold (LIDT) of optical fiber surfaces does not achieve values generally represented for properly treated fused silica. Therefore, broader testing and understanding of optical fibers surface laser induced damage threshold and influencing factors is a key in utilization of optical fibers in pulsed lasers.
An overview of Czech national R&D project HiLASE (High average power pulsed LASEr) is presented. The HiLASE project aims at development of pulsed DPSSL for hi-tech industrial applications. HiLASE will be a user oriented facility with several laser systems with output parameters ranging from a few picosecond pulses with energy of 5 mJ to 0.5 J and repetition rate of 1-100 kHz (based on thin disk technology) to systems with 100 J output energy in nanosecond pulses with repetition rate of 10 Hz (based on multi-slab technology).
The Czech national R&D project HiLASE is a platform for development of advance high repetition rate, diode pump solid
state lasers (DPSSL) systems with energies in the range from mJ to 10J and repetition rate from 10 Hz to 100 kHz. In this
paper an overview and a status of the project will be given. Additionally some applications of these lasers in the hi-tech
industry, which initiated their development, will be also presented.