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Martin Smrž

Publications and source records attributed to Martin Smrž.

9 recordsLinked to original sources

Scalable laser micro- and nanostructuring of mould inserts for functional injection-moulded polymer surfaces

Functional polymer surfaces with tailored wettability, antibacterial and adhesion properties are increasingly required in medical, packaging and consumer applications. Laser structuring of steel mould inserts followed by injection moulding offers a scalable manufacturing route, but conventional single-beam texturing has limited throughput. Here, we present a selective acceleration strategy that applies different laser techniques to micro- and nanostructuring. Deep microhole drilling was accelerated up to 20-fold by operating an ultrashort-pulse fibre laser at a repetition rate of 1 MHz in single-beam mode. For laser-induced periodic surface structures (LIPSS), line-beam shaping with a spatial light modulator increased productivity by 35-fold, reaching processing speeds above 100 cm$^2$ min$^{-1}$ while retaining sub-micrometre fidelity. Replication experiments with polypropylene (PP), PA66 and ABS confirmed successful transfer of micro- and nanostructures, with PP showing the highest fidelity. Vacuum-assisted injection moulding increased replicated feature height by 56--283 percent. All laser-textured PP surfaces showed higher static water contact angles than the untreated reference, reaching approximately $134^\circ$ in the Wenzel regime. Structured PA66 surfaces reduced bacterial retention by up to 99.8 percent for E. coli and approximately 90 percent for S. aureus. Laser texturing also increased the shear strength of PP joints bonded with a non-optimised adhesive by up to 30-fold. This approach provides a practical, coating-free route to functional polymer components and helps bridge the gap between laboratory laser texturing and industrial injection moulding.

physics.optics

Residual pump diagnostics of lasing-state absorption in multipass pumped Yb:YAG thin-disk lasers

Residual pump power was used as a spatially integrated diagnostic of inversion-dependent absorption in 32-pass pumped Yb:YAG thin-disk lasers. A quasi-three-level rate-equation model was coupled to accumulated pump flux, intracavity signal flux, and an effective ASE-induced depletion term. Two disks were tested under non-lasing and multimode lasing conditions. The analysis reproduced residual pump fractions within 2.4\% in non-lasing and 1.8\% in multimode operation, and output power within 1.3\% relative error. Stimulated emission reduced the steady-state inversion and increased the effective pump-band absorption relative to the non-lasing case, while the absorption remained below the room-temperature small-signal value. The same absorption state was then used to estimate volumetric heat-load trends and to assess pump-pass number and output-coupler transmission for high-power thin-disk scaling.

physics.optics

Analysis of multi-pass pumped thin-disk laser performance with measured disk deformation

Predicting the steady-state performance of high-power thin-disk lasers requires not only pump-signal energy transfer but also how disk deformation contributes intra-cavity mode formation. In this work, we address the output-power reduction that occurs even when the laser remains in a single-mode regime with $\mathrm{M^2}$ around 1.1. We developed a numerical model in which the pump-induced inversion is initialized from a non-lasing multi-pass absorption model and then coupled to two-dimensional cavity-field propagation using measured disk optical path difference (OPD) maps. Applied to the Yb:YAG thin-disk laser, the model reproduces the residual pump fraction and predicts the signal power, beam diameter, and $\mathrm{M^2}$ with errors of 3.0$\%$, 1.7$\%$, and 0.05, respectively. To interpret the measured OPD, the disk surface is further analyzed by Zernike decomposition, and the defocus term is converted into an equivalent radius of curvature (eROC). The eROC-based simulation provides the defocus-only reference performance that is theoretically reachable in the absence of higher-order aberrations, whereas the measured-OPD simulation reproduces the experimentally observed power reduction at high pump intensity. The comparison quantitatively shows that higher-order aberrations beyond defocus reduce the overlap with the fundamental cavity mode and limit power scaling, even before strong $\mathrm{M^2}$ degradation appears. This result identifies aberration-induced modal loss as a key limitation in high-power single-mode thin-disk lasers.

physics.optics

Comparative study of second harmonic generation at 1030 nm in BiBO and LBO crystals using a 100 W-class picosecond laser

We present a systematic experimental comparison of single-pass second-harmonic generation (SHG) in bismuth triborate (BiBO) and lithium triborate (LBO) nonlinear crystals, driven by a 1.3 ps, 91 kHz laser at 1030 nm with up to 57 W of average input power. Both crystals yielded 32 W of second harmonic (SH) output at 515 nm, corresponding to a conversion efficiency of 56 %, which to the best of our knowledge represents the highest SH output power reported in the green spectral region using a BiBO crystal. Power dependence, long-term stability, beam quality, pulse duration, spectral properties, thermal effects, and angular acceptance bandwidth are characterized and directly compared for both crystals. These results provide quantitative performance benchmarks to guide the selection of nonlinear crystals for high-average-power, ultrashort-pulse frequency conversion near 1030 nm.

physics.optics

Adaptive optics design for high-energy kW-class multi-slab laser amplifier

We demonstrate real-time wavefront correction in a high-energy high-average-power DiPOLE100/Bivoj laser using adaptive optics. A bimorph deformable mirror and Shack-Hartmann wavefront sensor reduced wavefront error tenfold and improved the Strehl ratio elevenfold. Design aspects such as deformable mirror actuator geometry, optimal placement, and loop frequency are discussed for integration into next-generation high-energy high-average-power lasers.

physics.optics

A comprehensive study of second and third harmonic conversion efficiency, angular and temperature tolerance, and long-term stability in LBO crystals using a 10-J-class laser

We present a study of second harmonic generation (SHG) and third harmonic generation (THG) in lithium triborate (LBO) crystals using a high-energy, 10-J-class, 10 Hz Yb:YAG laser system. We achieved high conversion efficiencies of 75% for SHG and 56% for THG for Gaussian-like temporal pulse shapes and top-hat-like beam profiles. The angular and temperature dependence of the LBO crystals were measured and validated through numerical simulations. The SHG process exhibited an angular acceptance bandwidth of 1.33 mrad and a temperature acceptance bandwidth of 2.61 K, while the THG process showed 1.19 mrad and 1.35 K, respectively. Additionally, long term stability measurements revealed RMS energy stabilities of 1.3% for SHG and 1.24% for THG. These results showcase the reliability of LBO crystals for high-energy, high-average-power harmonic generation. The developed system offers automated switching between harmonics provided at the system output. The system can be easily adapted to Nd:YAG based pump lasers as well.

physics.optics

70 MW-level picosecond mid-infrared radiation generation by difference frequency generation in AgGaS2, BaGa4Se7, LiGaSe2, and LiGaS2

Comparative study of nonlinear crystals for picosecond difference frequency generation in mid-IR is presented. Nonlinear crystals of AgGaS$_2$, BaGa$_4$Se$_7$, LiGaSe$_2$, and LiGaS$_2$ were studied. Samples of AgGaS$_2$, BaGa$_4$Se$_7$, LiGaSe$_2$, and LiGaS$_2$ were tested in thee sets having lengths of 2, 4, or 8 mm. In order to investigate the dependence of efficiency on the crystal length, three sets of crystals with lengths of 2, 4, or 8 mm were tested. The developed tunable DFG system was driven by the 1.03 $μ$m, 1.8 ps, Yb:YAG thin-disk laser system operated at the repetition rate of 10 or 100 Hz. As the best result, picosecond mid-IR pulses at a wavelength of $\sim$7 $μ$m with the energy up to 130 $μ$J corresponding to the peak power of $\sim$72 MW were generated using the 8 mm long LiGaS$_2$ crystal. Using the BaGa$_4$Se$_7$ crystal, DFG tunability in the wavelength range from 6 up to 13 $μ$m was achieved.

physics.optics

Power output optimization in complex laser systems by means of polarization control

Recently, the polarimetricmethod for thermally-induced polarization changes driven power losses (TIPCL) mitigation in complex laser systems has been developed. However, the final optimization relied on the four-parameter numerical process. This letter provides a fully analytical direct calculation alternative to this optimization process. The validity of this approach is demonstrated on the previously published data from pulsed laser system Bivoj/DiPOLE100. The new approach provides a deeper insight into the polarimetric method for TIPCL suppression and also brings a more precise, reliable, and faster alternative to the numerical process used earlier.

physics.optics

High power single crystal KTA optical parametric amplifier for efficient 1.4-3.5 $μ$m mid-IR radiation generation

In this paper, we present a single crystal, KTA (potassium titanyl-arsenate, KTiOAsO$_4$) based picosecond optical parametric amplifier pumped by an in-house built 1030 nm Yb:YAG thin-disk laser, capable of tunability from 1.46 to 3.5 $μ$m, operating at 90 kHz, with high average power in the signal and idler beams. The highest output power of 8.9 W was reached for the 1750 nm signal beam with 19% conversion efficiency and the respective 2500 nm idler beam power was 6.2 W with 13% efficiency. The highest combined signal and idler mid-IR power was obtained at 17 W at the 2060 nm wavelength degeneracy point.

physics.optics