Alexander Gaydardzhiev

Ultrabroadband operation of a femtosecond optical parametric generator based on BiB 3 O 6 in the near-IR

Ultrabroadband optical parametric generation in the near-IR (approximately 135 THz, 1.15-2.4 microm) is demonstrated using bismuth triborate, BiB(3)O(6) (BIBO), in a collinear geometry. The white light continuum energy obtained with a single stage reached 15 microJ (internal conversion efficiency of approximately 7%). Integral pulse durations as short as 63 fs were derived from the recorded FROG traces, comparable to the 45 fs pulse duration of the 1 kHz Ti:sapphire regenerative amplifier used for pumping at 800 nm.

High-energy, sub-30 fs near-IR pulses from a broadband optical parametric amplifier based on collinear interaction in BiB(3)O(6).

We report efficient generation of tunable femtosecond pulses in the near IR using a two stage, white-light seeded, collinear, femtosecond optical parametric amplifier (OPA). The OPA, based on BiB(3)O(6) crystal in both stages and pumped at 807 nm by a 1 kHz Ti:sapphire laser amplifier, provides sub-30 fs signal pulses after compression with energies exceeding 200 microJ, which corresponds to fivefold pulse shortening and approximately 30% internal conversion efficiency in the second stage considering 150 fs pump pulses with 1.5 mJ energy. The corresponding idler pulses with more than 100 microJ have sub-60 fs duration without compression. The first stage alone is capable of producing sub-20 fs pulses near 1400 nm at the microjoule level without using any compression.

Subnanosecond, mid-IR, 0.5 kHz periodically poled stoichiometric LiTaO3 optical parametric oscillator with over 1 W average power.

We report a subnanosecond mid-IR tunable optical parametric oscillator based on periodically poled stoichiometric lithium tantalate (PPSLT), pumped by an amplified single frequency microchip laser at 1064 nm at a repetition rate of 0.5 kHz. Using a 20 mm long PPSLT crystal polled with three different domain periods (30.2, 30.3, and 30.4 μm) and changing the temperature of the crystal from 20°C to 265°C, we achieved wavelength tuning between 2990 and 3500 nm. The high nonlinearity of the used medium and the large aperture (3.2 mm) ensure maximum idler output energy of ~2 mJ in the whole tuning range, corresponding to 18% idler conversion efficiency and more than 1 W of average power. 270 ps idler pulse durations were obtained as a result of the 818 ps pulse duration of the pump.

The application of the monoclinic BiB3O6 nonlinear crystal in ultrafast laser technology

BiB3O6 (BIBO), the first low-symmetry (monoclinic class 2) inorganic nonlinear crystal that became commercially available, possesses some unique advantages for applications in ultrafast laser technology which are primarily related to its dispersive properties. In the present paper, these properties are analyzed in more detail and compared with other crystals. Of special interest is the pumping of this material near 800 nm for broadband parametric amplification in the near-infrared between 1.15 and 2.4 μm. We present experimental results on generation and amplification of ultrabroadband femtosecond continua in this spectral range using amplified Ti:sapphire lasers as pump sources.

Near diffraction limited pulses with 52-mJ, 1.2 ns at 0.5 kHz, generated by Nd-based MOPA

In this work, we report the amplification of laser pulses from a near diffraction limited, passively Q-switched Nd:YAG master oscillator (0.58 mJ, 1.2 ns at 0.5 kHz) up to 52-mJ in a Nd:YVO4 preamplifier and two diode pumped boost YAG-amplifiers, whilst preserving pulse duration, beam quality and linear polarization.

5 mJ, sub-nanosecond PPSLT OPA at 0.5 kHz, tunable in the water absorption band at 3 microns

Summary form only given. Coherent mid-IR sources (2.5-4 μm) combining high average power and high pulse energy are essential for a great number of industrial, scientific and commercial applications. Furthermore, they have broad medical implications, due to the high water absorption around 3μm. Due to the limited choice of laser materials emitting directly in this spectral range, covering it can be efficiently achieved through nonlinear frequency conversion devices, pumped by Q-switched Nd-laser systems, operating at kHz repetition rates. A fundamental efficiency limitation in short-pulsed OPOs is the available resonant wave build-up time. In order to keep this time period small compared to the pump pulse duration in short cavity OPOs, one should make use of highly nonlinear optical media. Furthermore, pulsed OPOs reaching mJ level output are prone to optical component damage due to the high amount of energy circulating inside the OPO cavity [1]. Mid-IR OPO output can be scaled significantly beyond this threshold by employing an optical parametric amplification (OPA) stage, determining the output energy and efficiency of the whole system [2]. Naturally, given the potential benefits, the search for nonlinear materials for frequency conversion in mid IR have recently intensified [1, 2]. However for really high power (energy) frequency down-conversion devices in the spectral region between 2.5 and 4 μm, periodically poled stoichiometric lithium tantalate (PPSLT) with its low coercive field (0.8 kV/mm), high refraction damage threshold and transparency up to 5 μm, is amongst the very few suitable candidate.Here we demonstrate a highly efficient OPA system with high pulse energy at kilohertz repetition rate, seeded by a singly resonant OPO tunable between 3 and 3.5 μm. The OPO employs a 20 mm long, 10 mm wide, and 3.2 mm (along z axis) thick PPSLT crystal with three polled zones with different domain inversion periods (30.2, 30.3 and 30.4 μm). The OPA stage employs a similar 37 mm long crystal, which together with the OPO crystal is antireflection coated for the pump, signal and idler waves. The OPO cavity is 27 mm long with plane parallel mirrors, highly reflective for the signal wave. The output idler wave is collimated and then focused in the OPA by two CaF2 lens with 100 mm focal lengths. The pump source is a diode-pumped MOPA system providing 35 mJ pulses with high beam quality (Mx2 x My2=1.3 x 1.1), short pulse duration (1.2 ns), at 0.5 kHz repetition rate.The maximum output idler energy is 5.1 mJ, when seeded with 0.52 mJ at 3.04 μm, while the OPA pump energy is 27 mJ, corresponding to idler conversion efficiency of 18.3 % and total conversion efficiency of 48.4 % (Fig1.a). By changing the temperature of the two PPSLT crystals from 40°C up to 265°C and employing the three domain inversion periods, we were able to achieve continuous tunability from 3 to 3.5 μm. In order to measure the idler pulse duration we frequency doubled the idler wave in 3 mm thick KTP crystal. After deconvolution with the response function of the detection system we obtain 580 ps for the SH of the idler, corresponding to an idler pulse duration of 820 ps, expected shorter than the pump pulse duration (1.2 ns) - Fig.1b. The beam quality of the idler wave was Mx2 = 50 and My2 = 44 (Fig.1c). To the best of our knowledge, this is the first sub-nanosecond coherent source, that incorporates high energy pulses (up to 5.1 mJ) with high repetition rate (0.5 kHz) and tunability in this highly relevant for biomedical applications spectral region.

PPSLT KHz OPO/OPA tunable in 3–3.5 μm pumped by 1ns 30mJ Nd-laser system

We demonstrate 5.7-mJ mid-IR PPSLT based OPO/OPA pumped by 30-mJ 1.4 ns Nd-laser system operated at 0.5-kHz repetition rate. The output wavelength is temperature tuned within water absorption peak (3000-3500 nm).

13-mJ, single frequency, sub-nanosecond Nd:YAG laser at kHz repetition rate with near diffraction limited beam quality

Near diffraction limited, single frequency, passively Q-switched Nd:YAG laser (240-μJ, 830-ps at 0.5-kHz) is amplified up to 13-mJ in a three-stage diode pumped amplifier whilst preserving pulse duration, beam quality and linear polarization.

0.7 mJ, 0.5 kHz Mid-IR Tunable PPSLT Based OPO Pumped at 1064 nm

We report up to 0.72 mJ at 0.5 kHz, temperature tunable (3-3.5 µm) radiation from a sub-nanosecond PPSLT based singly resonant OPO, pumped by an amplified microchip laser at 1064 nm.

Single Frequency Multi Milijoule Sub-nanosecond Nd:YAG Laser at kHz Repetition Rate

We report up to 13 mJ at 0.5 kHz, linearly polarized output with 830 ps pulse duration from a single frequency amplified Nd:YAG microchip laser at 1064 nm