The usage of coherent radiation in the mid-infrared (mid-IR) wavelength range (2 – 8 μm) covers a wide spectrum of applications in many different fields. To satisfy the demand for a high-power, picosecond mid-IR source, we are developing an optical parametric system tunable between 1.45 and 3.5 μm in wavelength. The pumping of the system is provided by an in-house built Yb:YAG thin-disk laser, delivering 80 W of average power at 93 kHz pulse repetition rate, 1030 nm wavelength and ~1.3 ps pulse duration. The optical parametric system consists of a double-pass optical parametric generator (OPG) based on a periodically poled lithium niobate. By utilizing four periods of poling and temperature tuning, wavelength tunability range is from 1.45 to 3.5 μm. Maximum signal output power was around 85 mW at 1850 nm wavelength at 2 W pump power. Subsequent amplification of the signal generated in the OPG stage takes place in an optical parametric amplifier (OPA), which consists of a pair of walk-off compensating KTA crystals, pumped by up to 50 W average power. Maximum output signal and idler sum power after the OPA stage was 8.4 W. The wavelength tunability of the amplifier spans from 1.5 to 3.2 μm. Further increase in the tunability range as well as gapfree tuning is currently crystal mount-limited.
We report on the generation of picosecond pulses at 515 nm and deep ultraviolet pulses at 257 nm and 206 nm. They are generated as second, fourth and fifth harmonic frequencies of the high power diode-pumped Yb:YAG thin-disk laser at the fundamental wavelength of 1030 nm. The laser at the fundamental wavelength is based on a chirped-pulse amplification of oscillator pulses in two-stage regenerative amplifier based on thin-disks as active media. The diode pumping at the zero phonon line is used. The pulses are produced at ~100 kHz repetition frequency, 2-10 ps pulse duration and ≤2 mJ pulse energy. The fundamental beam is doubled in an LBO crystal at an efficiency of 42%. Subsequently the fourth harmonic frequency (257 nm) is produced by frequency doubling of the second harmonic frequency in a CLBO crystal. The unconverted part of the fundamental beam after SHG is used with the fourth harmonic beam as 1ω+4ω frequency sum in a further CLBO crystal for the fifth harmonic frequency (206 nm) generation. Two issues are important in the efficient optical conversion: nonlinear absorption given mainly by two-photon absorption (TPA) and proper timing of interacting pulses. In our simulations we take into account TPA and study the consequences of different timing of 1ω- and 4ω-pulses on the CLBO when generating the 5th harmonic. It was found that 1.4 ps delay of the 1ω-pulse after the 4ω-pulse is necessary to get the highest 5ω-output. Also the 5ω-pulse duration is affected by the timing.
Mid-IR wavelength range (between 2 and 8 μm) offers perspective applications, such as minimally-invasive neurosurgery, gas sensing, or plastic and polymer processing. Maturity of high average power near-IR lasers is beneficial for powerful mid-IR generation by optical parametric conversion. We utilize in-house developed Yb:YAG thin-disk laser of 100 W average power at 77 kHz repetition rate, wavelength of 1030 nm, and about 2 ps pulse width for pumping of a ten-watt level picosecond mid-IR source. Seed beam is obtained by optical parametric generation in a double-pass 10 mm long PPLN crystal pumped by a part of the fundamental near-IR beam. Tunability of the signal wavelength between 1.46 μm and 1.95 μm was achieved with power of several tens of miliwatts. Main part of the fundamental beam pumps an optical parametric amplification stage, which includes a walk-off compensating pair of 10 mm long KTP crystals. We already demonstrated the OPA output signal and idler beam tunability between 1.70-1.95 μm and 2.18-2.62 μm, respectively. The signal and idler beams were amplified up to 8.5 W and 5 W, respectively, at 42 W pump without evidence of strong saturation. Thus, increase in signal and idler output power is expected for pump power increase.
The Verdet constant dispersion of CeF3 crystal was measured in the spectral range from 0.45 to 1.95 μm. To the best of our knowledge, CeF3 crystal was investigated for the first time as a potential material candidate for near-infrared Faraday rotators (FRs). The experimental results obtained for Verdet constant dispersion were compared to other magneto-optical materials with the conclusion that CeF3 crystal possesses up to 60% higher Verdet constant in the near-infrared spectral region 1.1 to 1.5 μm compared to widely used terbium gallium garnet crystal. Furthermore, the presented experimental setup is capable of high precision measurement of Verdet constant dispersion in a broad spectral range, with measurement error not exceeding 5%, therefore, representing a powerful tool for FRs development.
In this paper, we investigated laser performance of Er:Y<sub>2</sub>O<sub>3</sub> ceramics at room temperature. With pulsed pumping with duty cycle of 1%, 1.02 W of peak output power was obtained at wavelength of 2.7 μm with slope efficiency of 3%. Furthermore, absorption spectra of the ceramics and temperature evolution for different pumping conditions were examined.
Relations among absorption of pump beam, quantum defect and thermal load were investigated for pump wavelengths of
968 nm and near 940 nm in two independent, real-time measurement experiments complemented with thermal
distribution simulation. Saturation of absorption at 969 nm pumping for non-lasing operational regime, which affects
temperature rise and exists independently of the thin disk type, disk head construction, pump power and pump beam
diameter is reported. Disk temperature dependence of absorption, quantum defect and disk geometry and large difference
between absorption, disk temperature and o-o efficiency at both pump wavelengths are discussed.
In this work, a passively mode-locked Yb:YGAG (Yb:Y<sub>3</sub>Ga<sub>2</sub>Al<sub>3</sub>O<sub>12</sub>) ceramic laser generating picosecond pulses at liquid-nitrogen temperature is demonstrated. The Yb:YGAG has a similar structure to Yb:YAG, but its emission bandwidth at cryogenic temperature remains much broader, which is advantageous for ultrashort pulse generation and amplification. Using this laser material, a stable train of pulses at a wavelength of 1026 nm was obtained, with measured pulse duration of 2.4 ps, which is more than four times shorter than that achieved with a cryogenically-cooled Yb:YAG.
We report on development of a 100-kHz, 5-mJ picosecond system based on a two-stage thin-disk Yb:YAG regenerative amplifier. With a compact ring cavity, we obtained 565 W with 46.7% optical-to-optical efficiency in continuous-wave. In seeded operation, pulses with energy up to 4 mJ and 1.4-nm bandwidth were generated with 39% extraction efficiency. Pulse compression below 2 ps was so far demonstrated at lower pulse energy of 1 mJ. Full-power pulse compression and further pulse energy increase are under development.
High average power picosecond Yb:YAG thin-disk lasers are being developed at Hilase. A compact 1 mJ/100 kHz and 4 mJ/100 kHz zero-phonon-line-pumped regenerative amplifiers PERLA C with a CVBG compressor provide <2 ps long pulses in a nearly diffraction-limited beam. The output was successfully converted to 2nd and 4th harmonic frequency with high conversion efficiency. High energy, QCW-pumped beamline PERLA B is operated at 45mJ/1kHz in fundamental spatial mode and pulse length < 2ps. Its second stage amplifier is being assembled and 1.8 J was extracted. The latest development status of all thin-disk beamlines at the Hilase center is reported.
We are developing an Yb:YAG thin disk regenerative amplifier operating at 1 kHz repetition rate which should deliver output of 100 W of average power which corresponds to the pulse energy of 100 mJ. In order to achieve such high output energy, large size mode matching on a thin-disk is required to avoid optical damage but on the other hand, larger mode area is more susceptible to the influence of optical phase distortions (OPD’s) thus limits achievable pulse energy and beam quality. We developed a compact setup allowing precise measurement of the thin-disk deformations by implementation of a Hartmann-Shack wavefront sensor and a single mode probe laser diode. In comparison to the interferometric measurement methods, our approach brings a number of advantages like simplicity of alignment, compactness and robustness, at the same time keeping the high precision of measurement in a range of few nanometers.
We present a diode-pumped actively mode-locked Tm:YLF laser. Continuous-wave mode-locked regime was achieved using an acousto-optic modulator and a stable train of pulses with 150 MHz repetition rate, 220 ps pulse width and 1.2 W average output power at 1.91 μm in a nearly diffraction-limited beam was obtained. Laser characteristics in the freerunning regime with both continuous and pulsed pumping as well as humidity-related issues are also reported.