Non-oxide Nonlinear Crystals Research Articles

Advances in the development of few-cycle gigawatt-peak-power mid-IR optical parametric amplifiers pumped by Cr:Forsterite laser using non-oxide nonlinear crystals

We demonstrate an experimental and theoretical comparison of non-oxide LiGaS2, HgGa2S4, and AgGaS2 crystals performance for wavelength conversion into the near and mid-IR range 1.5–8 μm in optical parametric amplifier pumped by Cr:Forsterite laser, delivering 100 fs pulses at 1.24 μm. It is shown that exceptionally high total energy conversion efficiency into the idler (4–5 μm) and signal (1.65–1.8 μm) waves up to 18% can be achieved using the HGS crystal, providing high nonlinearity, while the LGS crystal is more preferable for generating few-cycle mid-IR pulses due its unique dispersive properties. Our source features high peak power in gigawatt regime (0.4–2.4 GW) with pulse duration below 80 fs and optical synchronization with high harmonic generation (HHG) and THz beamlines, which is ideal for pump-probe experiments of nonlinear and strong-field physics.

Hardness and Young's modulus of BaGa4S7 and BaGa4Se7 nonlinear optical crystals

We report hardness and Young's modulus measurements of two recently developed non-chalcopyrite, non-centrosymmetric crystals, BaGa4S7 and BaGa4Se7, which seem very promising for three-wave parametric interactions in the mid-IR part of the spectrum between 5 and 18 μm. The obtained averaged values for the hardness from nanoindentation tests, converted into Vickers hardness number, are 556 kg/mm2 for the sulphide and 336 kg/mm2 for the selenide compound, respectively. Knowledge of these values will be essential for proper polishing and fabrication of optical elements, the wide use and commercialization of these novel non-oxide nonlinear crystals, which possess a number of other advantages over classical chalcopyrites operating in the same spectral window.

Radiation source based on an optical parametric oscillator with MgO : PPLN crystal and volume Bragg grating, tunable in ranges of 2050 – 2117 and 2140 – 2208 nm

A tunable radiation source based on an optical parametric oscillator (OPO) with a periodically poled lithium niobate (PPLN), generating light with a wavelength of ∼2.1 μm in a near-degenerate regime, is developed. The use of a volume Bragg grating (VBG) as a selective element makes it possible to reduce significantly (by a factor of more than 180) the radiation linewidth. Wavelength tuning from 2050 to 2117 nm for the signal wave and from 2140 to 2208 nm for the idler wave is demonstrated. The maximum average OPO output power is found to be 617 mW (123 μJ), which corresponds to a conversion efficiency of 10 %. The use of a VBG provides a fundamental possibility of designing a pump source with a small linewidth (of no more than 1 nm) and smooth wavelength tuning in a desired range for frequency converters based on non-oxide nonlinear crystals generating mid-IR light (5 – 15 μm).

Femtosecond 8.5 μm source based on intrapulse difference-frequency generation of 2.1 μm pulses.

We report on a femtosecond ∼8.5 μm, ∼2 μJ source based on the intrapulse difference-frequency generation (DFG) of 2.1μm pulses in an AgGaSe2 (AGSe) crystal. Compared to the conventional ∼0.8 or 1μm near-infrared (IR) pulses, a ∼2 μm driver for intrapulse DFG can provide more efficient conversion into the wavelengths longer than 5μm due to a lower quantum defect and is more suitable for the non-oxide nonlinear crystals that have a relatively low bandgap energy. Using 26fs, 2.1μm pulses for type-II intrapulse DFG, we have generated intrinsically carrier-envelope phase-stable idler pulses with a conversion efficiency of 0.8%, which covers the wavelength range of 7-11μm. Our simulation study shows that the blueshift of intrapulse DFG is assisted by self-phase modulation of the driving pulses in AGSe. The idler pulses are particularly useful for strong-field experiments in nanostructures, as well as for seeding parametric amplifiers in the long-wavelength IR.

Progress in 1-μm Pumped Mid-IR Optical Parametric Oscillators Based on Non-Oxide Nonlinear Crystals

Pumping mid-IR optical parametric oscillators near 1 μm is attractive for its simplicity and power scaling capability. To this aim, wide bandgap non-oxide nonlinear crystals are needed. This paper reviews the recent developments in crystal growth and singly resonant optical parametric oscillators for the generation of high single pulse energy and average powers in the mid-IR from 3 to 10 μm.

Optical damage studies of mercury thiogallate nonlinear crystals for use in 1-μm pumped optical parametric oscillators

We investigated optical damage (surface and bulk) in one of the most promising wide bandgap nonoxide nonlinear crystals, HgGa2S4, that can be used in ∼1-μm pumped optical parametric oscillators (OPOs) and synchronously pumped OPOs (SPOPOs) for generation of idler pulses above 4 μm without two-photon absorption losses at the pump wave- length. The optical damage has been characterized at the pump wave- length for different repetition rates using uncoated and antireflection- coated (mainly with a single layer for pump and signal wavelengths) sam- ples. HgGa2S4 is the most successful nonlinear crystal (both in terms of output energy and average power) for such OPOs, but optical damage inside the OPO has a lower threshold and represents at present the prin- cipal limitation for the achievable output. It is related to peak pulse and not to average intensity, and bulk damage in the form of scattering centers occurs before surface damage. Such bulk damage formation is faster at higher repetition rates. Lower repetition rates increase the lifetime of the crystal but do not solve the problem. The safe pump fluence in extrac- avity measurements is <1 J∕cm 2 , which corresponds to ∼100 MW∕cm 2 for the 8-ns pulse duration (both values peak on-axis). In the OPO, how- ever, peak on-axis fluence should not exceed 0.3 J∕cm 2 limited by the formation of bulk scattering centers in orange-phase HgGa2S4. In the nanosecond OPO regime, the damage resistivity of Cd-doped HgGa2S4 is higher and that of the almost colorless CdGa2S4 is roughly two times higher, but the latter has no sufficient birefringence for phase-matching. In SPOPOs operating in the ∼100 MHz regime, the dam- age limitations are related both to the peak pulse and the average inten- sities, but here HgGa2S4 seems the best nonoxide candidate to obtain first steady-state operation with Yb-based mode-locked laser pump sources. © 2013 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10