Changing debris orbits using High Power Pulsed Laser Interaction (HP PLI) finds interest in the Low-Earth Orbit (LEO) due to space debris congestion. Laser facilities allowing both high energy and repetition rate of a short pulsed irradiation become available as provided by the high power HiLASE beamline facility (Prague, CZ) with BIVOJ (100J, 10ns, 10Hz, 1030nm). In order to illustrate such an application, originally Crookes radiometer concept was adapted to quantify the efficiency of repeated laser shots in increasing rotating speed according to laser matter interaction. Various materials, from model to space applicative materials, allowed to estimate the material response with various irradiation characteristics (single shots vs. repeated shots). Matter behaviors (ablation, cratering, spallation, perforation) bracketed the laser conditions suitable in the perspective of laser propulsion with limited creation of extra debris or irradiated structures damages. Next is to strengthen the robustness of the simulation/experiment dialog to use simulation as a predesign tool for laser space propulsion.
Laser amplifiers producing high energy (multi-J) nanosecond pulses at high repetition rate (multi-Hz) are required for a wide range of commercial and scientific applications. The DiPOLE concept, developed at the STFC Central Laser Facility (UK), consists in scalable, high-energy DPSSL amplifiers based on cryogenically-cooled, multi-slab ceramic Yb:YAG. In this work we discuss the most recent developments aimed at scaling the pulse repetition of new generation DiPOLE lasers from 10 Hz to 100 Hz. We present the design and current status of a 10 J, 100 Hz DiPOLE laser. We will discuss thermal management approaches adopted for this system.
Crytur is a company with long tradition of growing and processing crystals for technical applications, with history reaching back to 1943. Recently we have developed Crystal Improved Growth (CRIG) method for production of large core-free single crystals of YAG. The diameter currently achieved is 140 mm (in case of undoped crystal), and the crystal weight is up to 10 kg. The method was used to grow un-doped YAG crystals, YAG:Ce crystals for large scintillating screens, and Yb:YAG and Nd:YAG for high power solid-state laser systems.
Large laser slabs were manufactured from Yb:YAG doped crystals for Diode-Pumped Solid State Laser (DPSSL) system Amos, which operates within Extreme Light Infrastructure in the Czech republic (ELI Beamlines). The dimension of the largest Yb:YAG laser slab produced is 120×120×8 mm, there is no visible stress under crossed polarizers and the wavefront distortion in the clear aperture region is smaller than λ/10 (λ=633 nm) in its Peak-to-Valley value. The edges of the slab are from diffusively bonded Cr:YAG cladding in order to suppress ASE (Amplified Spontaneous Emission).
In 2018 the performance of three sets of laser slabs (ø55x5 mm) with differently realized ASE suppression was characterized at cryogenic temperatures at HiLASE Centre in terms of small signal gain measurements as well as amplification test under 30 J pumping at 1 Hz and 10 Hz repetition rates. We provide data that show that the crystal slabs have comparable properties to the ceramic slabs (produced by Konoshima company, Japan) currently in use at HiLASE.
The HiLASE “Bivoj” laser system developed at CLF Rutherford Appleton Laboratory in collaboration with HiLASE team as DiPOLE100 was relocated to Dolni Brezany near Prague, Czechia at the end of 2015 and fully re-commissioned at the end of 2016. In 2016, the system demonstrated average output power of 1kW generating pulses of 105 J at 10 Hz repetition rate for the first time in the world. Since then the system has been subjected to several testing campaigns in order to determine some of its key characteristics. Beam quality, wavefront quality, pointing stability, energy stability and experience with long term operation of 1 kW laser are presented. In addition, depolarization effects have been detected inside the main amplifier. Details on these results along with numerical simulations are presented.
The concept of system for intracavity interferometry based on the beat note detection in subharmonic synchronously intracavity pumped optical parametrical oscillator (OPO) is presented. The system consisted of SESAM-modelocked, picosecond, diode pumped Nd:YVO4 laser, operating at wavelength 1.06 μm and tunable linear intracavity pumped OPO based on MgO:PPLN crystal, widely tunable in 1.5 μm able to deliver two independent trains of picosecond pulses. The optical length of the OPO cavity was set to be exactly twice the pumping cavity length. In this configuration the OPO produces signal pulses with the same repetition frequency as the pump laser but the signal consists of two completely independent pulse trains. For purpose of pump probe measurements the setup signal with half repetition rate and scalable amplitude was derived from the OPO signal using RF signal divider, electropotical modulator and fiber amplifier. The impact of one pump beam on the sample is detected by one probing OPO train, the other OPO train is used as a reference. The beat note measured using the intracavity interferometer is proportional to phase modulation caused by the pump beam. The bandwidth of observed beat-note was less than 1 Hz (FWHM), it corresponds to a phase shift measurement error of less than 1.5 × 10-7 rad without any active stabilization. Such compact low-cost system could be used for ultra-sensitive phase-difference measurements (e.g. nonlinear refractive index measurement) for wide range of material especially in spectral range important for telecom applications.
We present an efficient zero-phonon-line pumped cryogenic Yb:YAG laser passively Q-switched by Cr:YAG with different initial transmissions. At 140K, with 85% initial transmission of Cr:YAG, a maximum average output power of 5.19 W with a repetition rate of 24.7 kHz was achieved leading to a slope efficiency of 55.7%. The maximum pulse energy, minimum pulse width and peak output power obtained in this case were 0.21 mJ, 142 ns and 1.48 kW respectively.
In this work, we have shown the possibility of performing pulsed laser operation at cryogenic temperature with innovative modular compact laser cavity. Using Yb:YAG/Cr:YAG configuration, at cryogenic temperature, in the preliminary laser experiments, we obtained a maximum average output power of 2.7 W with a repetition rate of around 50 kHz. The minimum pulse width, maximum pulse energy and peak power obtained were 2.5 ns, 60 μJ. and 25 kW respectively. To the best of our knowledge, an experimental approach on compact pulsed Q-switched lasers based on Yb:YAG/Cr:YAG at cryogenic temperature is tried for the first time.
We have characterized ytterbium–doped fiber laser and described in detail the effect of pump wavelength on self–induced laser line sweeping (SLLS). SLLS is a transient laser regime manifested by a relatively slow laser line shifting and usually observed in the near of pump laser threshold. The fiber laser under consideration is cladding–pumped by a temperature stabilized multimode laser diode (LD) at about 976 nm. The output wavelength of the diode is tunable by changing the diode temperature and current through the diode. The cavity of the laser is formed by perpendicularly cleaved fiber ends. Using this laser layout we made detailed study of sweeping dependences on pump wavelength by adjustment of the LD current and LD case temperature. The laser manifested laser line sweeping within the range of 5–7 nm on a wide span of pump laser diode power and temperature: 15–45°C LD temperature scale and pump range reaching to more than twice the amount of excess over threshold. We performed the measurement of the laser line sweeping span, period and rate as the dependence of pump wavelength.
We report laser line self-sweeping phenomenon in rare-earth doped fiber lasers. The effect of self-sweeping is observed in erbium-doped fiber laser and also in the ytterbium-doped one. The former, having linear layout, is core-pumped by laser diode (LD) at 980 nm. Laser cavity is formed with fiber loop mirror and angle cleaved fiber end. Laser operation is delimited by tunable filter; we observed sweeping regime in 0.5 nm wide interval defined by the filter. Yb-doped allfiber laser has linear layout as well. Laser is cladding-pumped by LD at about 976 nm; cavity is constrained by rightangle cleaved fibers. We observed laser line sweeping having a range of 6 – 8 nm. We characterized both lasers with respect to sweeping properties thoroughly. We present output laser line wavelength and instant output intensity versus time; we show dependence of sweeping range, sweeping rate, and sweeping period on output laser power and pump laser temperature (pump laser wavelength).
Rare-earth doped fiber lasers are subject to instabilities and various self-pulsed regimes that can lead to catastrophic
damage of their components. An interesting self-pulsing regime accompanied with laser wavelength drift with time is the
so called self-induced laser line sweeping (SLLS). Despite the early observations of the SLLS in solid-state ruby lasers,
in fiber lasers it was first time mentioned in literature only in 2009 where such a laser wavelength drift with time was
observed in a relatively broad range of about 1076 -1084 nm in ring ytterbium-doped fiber laser (YDFL). The main
characteristic of the SLLS is the scanning of the laser wavelength from shorter to longer wavelength, spanning over large
interval of several nanometers, and instantaneous bounce backward. The period of this sweeping is usually quite long, of
the order of seconds. This spectacular effect was attributed to spatial-hole burning caused by standing-wave in the laser
cavity. In this paper we present experimental investigation of the SLLS in YDFLs in Fabry-Perot cavity and ring
cavities. The SLLS was observed also in erbium-doped fiber laser around 1560 nm. We present for the first time
observation of the laser wavelength sweep in reverse direction, i.e., from longer towards shorter wavelengths. It was
observed in YDFL around 1080 nm.
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