We present pulse compression by double-pass spectral broadening in ZnS, KGW and YAG crystals pumped with 16 W average power amplified Yb:KGW oscillator pulses at a 76 MHz repetition rate. We demonstrate nearly transform-limited compressed laser pulses with excellent spatio-spectral homogeneity of the beam. This relatively simple and cost-effective method for pulse compression is applicable to almost any high-average power and low pulse energy laser system. It has the potential to open the opportunities for applications in ultrafast spectroscopy systems operating at pulse repetition rates in the tens or hundreds of MHz.
In this work we showcase an effective approach to substantially broaden the tuning range of microlaser-based parametric devices into the visible and UV-A spectral domains. We demonstrate the first subnanosecond pulse duration OPA continuously tunable throughout the VIS and UV-A spectral ranges. Our BBO crystal-based OPA was pumped by third harmonic (355 nm) 500 ps pulses from passively Q-switched Nd:YAG microlaser while the seed source was formed from multigrating MgO-doped periodically poled lithium niobate (MgO:PPLN) OPG-based seeder pumped by the second harmonic (532 nm) of the same microlaser. The OPA signal wave was continuously tunable from 419 nm to 728 nm via birefringent phase matching and maintained high beam quality. Unlike conventional supercontinuum seeders, the MgO:PPLN OPG seeder achieved much higher spectral power density which was crucial in achieving up to 19% OPA signal to pump conversion efficiencies. The introduction of the upconversion stage extended the tuning range of the system to 345 nm. A comprehensive characterization of both the seed source and the OPA was conducted, including energy, spatial, spectral, and temporal properties.
We present a comparative experimental study of supercontinuum generation in undoped KGW and YVO4 crystals pumped with near-IR femtosecond laser pulses. We demonstrate that KGW and YVO4 crystals, compared to commonly used sapphire and YAG, have significantly lower supercontinuum generation thresholds, produce remarkably larger red-shifted spectral broadenings and exhibit durable damage-free long-term operation at 2 MHz and 76 MHz repetition rates. Our results show that KGW and YVO4 crystals are excellent nonlinear materials for high repetition rate infrared supercontinuum generation which could be used for the design of high average power optical parametric amplifiers as well as for the development of ultrafast ultrafast spectroscopic and high-speed imaging systems.
We present a flexible and automated technique to evaluate the quality of periodically poled crystals throughout their entire volume. By translating the crystal perpendicular to the pump laser beam and recording the parametric signal conversion efficiency simultaneously, we were able to quantitatively describe the homogeneity of the ferroelectric domain structure in periodically poled lithium niobate (MgO:PPLN) and potassium titanyl phosphate (Rb:PPKTP) crystals. This analysis included crystals with single, multi, and fan-out grating designs. Such evaluation is non-destructive, achieves precise control and resolution, and provides a practical assessment of the overall efficiency of the quasi-phase-matched device.
Subnanosecond pulse duration optical parametric generator (OPG) based on fan-out grating design MgO:PPLN crystal is demonstrated. In a fan-out grating design crystal, the effective grating period and thus quasi-phase-matching (QPM) conditions change continuously throughout the width of the crystal. We show that the OPG, based on a fan-out periodically poled crystal and pumped by a micro-laser system, permits a compact and effective subnanosecond coherent light source that could be rapidly, widely, and continuously tunable in the near-infrared spectral region (1.4- 4.4 μm) just by laterally displacing the crystal with up to 50% conversion efficiency. Full characterization of the OPG is performed and the feasibility of broadband OPG output is evaluated with the addition of numerical calculations based on a nonlinear model.
This work has received funding from European Regional Development Fund (project No. 01.2.2-LMT-K-718-03-0004) under grant agreement with the Research Council of Lithuania (LMTLT).
Optical parametric light generation is a unique way to obtain continuously tunable laser radiation in a wide spectral region. Relatively inexpensive and compact subnanosecond (100 ps - 1 ns) optical parametric generators (OPG) with broad wavelength tunability are needed for a variety of applications that do not require the high temporal resolution supplied by expensive and sophisticated ultrashort (<10 ps) laser systems, but nanosecond (>1 ns) time resolution is not sufficient. Such applications are spectroscopy, laser-induced fluorescence, detection of chemical materials, nonlinear microscopy, biochemical research and differential absorption lidar to name a few. Development and the reduced cost of the passively Q-switched micro-laser manufacturing technologies permits them to be used as a high energy pump source for subnanosecond OPGs. Such micro-laser pumped subnanosecond OPGs would allow the implementation of low-cost, compact, continuously tunable laser radiation sources suitable for the aforementioned applications, especially in near-infrared (NIR) and visible (VIS) spectral ranges where the demand is high. To date, no subnanosecond OPGs based on short (up to 2 cm in length) periodically poled (PP) crystals have been demonstrated that could also be continuously tunable over a wide spectral range. Long PP crystals are more expensive, therefore implementation and investigation of such OPGs would be commercially attractive. Here we investigate parametric light generator based on short (up to 2 cm in length) periodically poled lithium niobate (PPLN) crystal pumped by 473 ps pulses from a 1 mJ energy micro-laser. Experimentally measured spatial, temporal and energy characteristics of the generated light from different length PPLN crystals are shown and supplemented by numerical simulations of parametric generation in a nonlinear dispersive medium.
This work has received funding from European Regional Development Fund (project No. 01.2.2-LMT-K-718-03-0004) under grant agreement with the Research Council of Lithuania (LMTLT).
The piezoelectric ringing phenomenon for the Pockels cell with DKDP crystal is analyzed. The dependencies of contrast ratio of Pockels cell with the DKDP crystal on high-voltage pulse duration in the range from 100 ns up to 5 μs and on the pulse frequency in range from 50 Hz to 250 kHz are obtained and analyzed. Measurements that map the piezoelectric ringing amplitude distribution in the aperture of the DKDP crystal of the Pockels cell are performed as well.
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