D. B. Kolker

Optical, thermal, electrical, damage, and phase-matching properties of lithium selenoindate

Lithium selenoindate (LiInSe2) is a new nonlinear chalcogenide biaxial crystal, related to LiInS2 and transparent from 0.54 to 10 μm at the 50% level (10 mm thickness), which has been successfully grown in large sizes and with good optical quality. We report on what we believe to be new physical properties that are relevant for laser and nonlinear optical applications and summarize all relevant characteristics, both from the literature and as measured in the present work. With respect to AgGaS(e)2 ternary chalcopyrite materials, LiInSe2 displays a nearly isotropic thermal expansion behavior with three- to five-times-larger thermal conductivities associated with high optical damage thresholds, and low intensity-dependent absorption, allowing direct high-power downconversion from the near-infrared, especially 1064 nm, to the deep mid-infrared. Continuous-wave difference-frequency generation (5.9–8.1 μm) of Ti:sapphire laser sources is reported for the first time as well as nanosecond optical parametric oscillation with a Nd:YAG laser as the pump source at 100 Hz and idler tuning between 4.7 and 8.7 μm.

Midinfrared optical parametric oscillator based on the wide-bandgap BaGa 4 S 7 nonlinear crystal

The orthorhombic biaxial crystal BaGa(4)S(7) has been employed in a 1064 nm pumped optical parametric oscillator generating <6 ns long idler pulses with energies as high as 0.5 mJ at 6.217 μm and average power of ~50 mW at 100 Hz. Notwithstanding the relatively low nonlinearity, ~3 times above threshold operation has been achieved at pump intensities more than 5 times below the crystal surface damage limit.

Nd:YAG pumped nanosecond optical parametric oscillator based on LiInSe2 with tunability extending from 4.7 to 8.7 µm

LiInSe(2) is one of the few (only 5) non-oxide nonlinear optical crystals whose band-gap (2.86 eV) and transparency allowed in the past nanosecond optical parametric oscillation in the mid-IR without two-photon absorption for a pump wavelength of 1064 nm. However, the first such demonstration was limited to the 3.3-3.78 microm range for the idler and the average idler power did not exceed 2.5 mW. Here we report broadly tunable operation, from 4.7 to 8.7 microm, of an OPO based on LiInSe(2), achieving maximum idler pulse energy of 282 microJ at approximately 6.5 microm, at a repetition rate of 100 Hz (approximately 28 mW of average power).

Cascaded optical parametric oscillation with a dual-grating periodically poled lithium niobate crystal

We demonstrate continuous-wave cascaded optical parametric oscillation in which the signal field of the primary parametric oscillator internally pumps the secondary parametric oscillator. Wavelength tuning is achieved with temperature tuning and a fan-out grating structure of a dual-grating periodically poled lithium niobate crystal. Above the secondary threshold the primary signal power is clamped, and all the other output powers increase linearly with the input pump power, in accordance with theory. Cascaded parametric oscillation offers a convenient and efficient way to generate multiple tunable outputs.

LaserBreeze gas analyzer for noninvasive diagnostics of air exhaled by patients

A laser gas analyzer has been designed for determining the composition of exhaled air by means of photoacoustic spectroscopy. The analyzer, based on a broadband optical parametric oscillator and photoacoustic detector, provides high-precision rapid analysis of the multicomponent composition of human exhaled air for dynamic estimation of the efficiency of treating bronchus and lung diseases.

A nanosecond optical parametric oscillator in the mid-IR region with double-pass pump

An optical parametric oscillator (OPO) with double-pass pump based on MgO:PPLN and PPLN periodic structures is described. A compact nanosecond Nd:YLF laser has been used as a pump source at 1.053 μm (the pumping pulse duration is 5–7 ns at a maximum pulse energy of 300 μJ at frequencies of 1–7 kHz). The oscillation threshold of the OPO based on MgO:PPLN was varied in a range of 11–28 μJ at wavelength of 2.1–4.3 μm. The conversion efficiency from the pump wave to an idler wave decreased from 8.6 to 2.5% in the range of 2.0–4.3 μm. For PPLN-OPO the measured threshold was 36 μJ at 4.2 μm and 49 μJ at 4.7 μm. The conversion efficiency of the pump energy into the energy of an idler wave was 3.3μ-0.4% at wavelengths of 4.2–4.7 μm.

Broadly tunable liinse2 optical parametric oscillator pumped by a nd: yag laser

LiInSe2 is one of the few (in the meanwhile 6) non-oxide nonlinear crystals whose band-gap (2.86 eV) and transparency enabled in the past nanosecond optical parametric oscillation in the mid-IR without two-photon absorption for a pump wavelength of 1064 nm. However, the first such demonstration was limited to the 3.34-3.82 μm spectral range with a maximum idler energy of 92 μJ at 3.457 μm for a repetition rate of 10 Hz. Now we achieved broadly tunable operation, from 4.65 to 7.5 μm, with a single crystal, reaching maximum idler pulse energy of 282 μJ at 6.514 μm, at a repetition rate of 100 Hz (~28 mW of average power).

Self-phase locking in 3-to-1 triply and doubly resonant optical parametric oscillators

We have observed self-phase locking in a triply and doubly resonant optical parametric oscillator containing a periodically poled lithium niobate crystal with a two-section grating that is designed for an exact 3-to-1 frequency division.

Optical trigger based on a fiber-coupled liquid crystal

Triggering capability of a laser radiation transmission through a fiber-coupled nematic liquid crystal (NLC) was experimentally investigated. This capability arises from light-induced reorientation of NLC molecules that enables self-focusing and self-confinement of propagating laser radiation. It was shown, that triggered optical coupling of two single-mode optical fibers terminated coaxially in NLC can be achieved through a self-induced light guide. It allows implementation of a miniature all-fiber devise, which can act as a precision power-sensitive optical trigger.

Mercury thiogallate nanosecond optical parametric oscillator continuously tunable from 4.2 to 10.8 μm

We demonstrate an optical parametric oscillator based on two HgGa2S4 crystals with an extremely wide tuning range from 4.2 to 10.8 μm. The HgGa2S4 optical parametric oscillator was pumped by a Q-switched nanosecond Nd : YLF laser at 1.053 μm. The absorption spectrum of ammonia was presented to demonstrate the feasibility of the developed optical parametric oscillator system for spectroscopic measurements and gas detection.