Malcolm H. Dunn

Low-pump-threshold continuous-wave singly resonant optical parametric oscillator

We describe a compact all-solid-state continuous-wave singly resonant optical parametric oscillator (SRO) with a minimal pump-power requirement. The SRO is based on periodically poled LiNbO(3) as the nonlinear material and is pumped by a 1-W diode-pumped Nd:YVO(4) minilaser at 1.064 microm . By exploiting the intracavity pumping technique in a 50-mm crystal, we have achieved SRO operation threshold at a diode pump power of only 310 mW.At 1 W of input diode power, the SRO delivers 70 mW of output power in the nonresonant idler at 3.66 microm , at a photon conversion efficiency of 55%. Multiparameter tuning of the SRO yields a signal wavelength range from 1.45 to 1.60 microm and an idler wavelength range from 3.16 to 4.02 microm in the mid infrared. The device is characterized by robust turnkey operation and long-term amplitude-stable performance.

Coma compensation in off-axis laser resonators

Abstract Coma can introduce large linear losses in laser resonators with off-axis focusing. Compensation of coma and astigmatism is considered for a variety of resonator arrangements. It is demonstrated that it is only possible to compensate for both at a unique off-axis angle. A resonator design is proposed for eliminating coma and astigmatism.

Stable, continuous-wave, intracavity, optical parametric oscillator pumped by a semiconductor disk laser (VECSEL).

We report relaxation oscillation free, true continuous-wave operation of a singly-resonant, intracavity optical parametric oscillator (OPO) based upon periodically-poled, MgO-doped LiNbO3 and pumped internal to the cavity of a compact, optically-excited semiconductor disk laser (or VECSEL). The very short upper-laser-state lifetime of this laser gain medium, coupled with the enhancing effect of the high-finesse pump laser cavity in which the OPO is located, enables a low threshold, high efficiency intracavity device to be operated free of relaxation oscillations in continuous-wave mode. By optimizing for low-power operation, parametric threshold was achieved at a diode-laser power of only 1.4 W. At 8.5 W of diode-laser power, 205 mW of idler power was extracted, indicating a total down-converted power of 1.25 W, and hence a down-conversion efficiency of 83%.

Continuous-wave, singly resonant, intracavity parametric oscillator

Performance characteristics of a continuous-wave intracavity optical parametric oscillator are described by use of an experimental arrangement comprising a KTP singly resonant oscillator located within a Ti:sapphire laser cavity and analyzed by use of a steady-state model. Internal and external powers, circulating fields, tuning ranges, spectral bandwidths, and amplitude-stability levels are measured and discussed. The nonresonant idler tunes from 2.53 to 2.87 microm, delivers a maximum output power of approximately 0.4W and displays long-term amplitude-stable operation. The total downconverted power approaches the optimum power coupled out of the Ti:sapphire laser in the absence of frequency conversion.

Continuous‐wave, dual‐cavity, doubly resonant, optical parametric oscillator

We have demonstrated a continuous‐wave optical parametric oscillator that uses separate optical cavities to resonate independently the nondegenerate signal and idler frequencies. The three‐mirror cavity utilizes the type II phase‐matching geometry in lithium triborate, with the orthogonally polarized signal and idler fields separated by an intracavity, dichroic‐coated, Brewster‐angled beam splitter. This dual‐cavity oscillator can overcome mode and cluster hopping effects, which are characteristic of doubly resonant, continuous‐wave optical parametric oscillators. We measure a pump power threshold of ≊200 mW and smooth tuning over ≊0.4 GHz. The tuning range is limited by pump resonance effects within the idler cavity.

An excimer-pumped beta -BaB/sub 2/O/sub 4/ optical parametric oscillator tunable from 354 nm to 2.370 mu m

A pulsed singly resonant optical parametric oscillator (OPO) has been constructed which can provide tunable coherent radiation over the entire wavelength range extending from 354 nm in the near ultraviolet, throughout the visible, to 2.370 mu m in the near infrared using a single beta -BaB/sub 2/O/sub 4/ crystal. The oscillator is pumped at 308 nm by a pulsed narrow band injection-seeded XeCl excimer laser in a near-field pumping configuration, and energy conversion efficiencies (optical-to-optical) in excess of 10% have been obtained in a 12-nm-long crystal across the OPO tuning range. The requirements placed upon the spectral and spatial coherence of the pump laser for optimum OPO operation are discussed. Experimental results on several oscillator parameters, including tuning range, oscillation threshold, energy conversion efficiency, and spatial and temporal characteristics, are presented. >

Continuous-wave singly resonant pump-enhanced type II LiB(3)O(5) optical parametric oscillator.

We report what is to our knowledge the first demonstration of a pump-enhanced singly resonant continuous-wave optical parametric oscillator. The nonlinear material used was lithium triborate cut for noncritical phase matching along the z axis, and the device was pumped by a single-frequency argon-ion laser. The oscillation threshold was ~1.0 W at 514.5 nm. For 3.4 W of pump power, we obtained single-frequency output powers of 500 mW in the nonresonant wave, which we temperature tuned over 14 nm.

Mid-infrared photonic crystal waveguides in silicon

We demonstrate the design, fabrication and characterization of mid-infrared photonic crystal waveguides on a silicon-on-insulator platform, showing guided modes in the wavelength regime between 2.9 and 3.9 µm. The characterization is performed with a proprietary intra-cavity Optical Parametric Oscillator in a free space optical setup and with a fibre coupled setup using a commercial Quantum Cascade Laser. We discuss the use of an integrated Mach-Zehnder interferometer for dispersion measurements and report a measured group velocity of up to a value of n(g) = 12, and determine the propagation loss to be 20 dB/cm.

Hyperspectral imaging of gases with a continuous-wave pump-enhanced optical parametric oscillator

We demonstrate a system for the active real-time hyperspectral imaging of gases using a combination of a compact, pump-enhanced, continuous-wave optical parametric oscillator as an all-solid-state mid-infrared source of coherent radiation and an electro-mechanical polygonal imager. The wide spectral coverage and high spectral resolution characteristics of this source means that the system is capable of being selectively tuned into the absorption features of a wide variety of gaseous species. As an example we show how the largest absorption coefficient exhibited by methane at 3057.7cm(-1) can be accessed (amongst others) and gas plumes imaged in concentrations as low as 30ppm.m using a parametric oscillator based on periodically-poled RbTiOAsO(4) (PP-RTA).

Continuous-wave optical parametric oscillator based on periodically poled KTiOPO 4 and its application to spectroscopy

We report a continuous-wave, doubly resonant optical parametric oscillator (OPO) based on the nonlinear material periodically poled KTiOPO4 and its application to spectroscopy. The OPO, which is pumped by a diode-pumped frequency-doubled Nd:YLF laser at 523 nm, has a low pump-power threshold of 25 mW and can deliver 10 mW of single-frequency output at 1.65 mu m for a pump power of 200 mW. The idler wavelength can be temperature tuned at a rate of 0.73 nm/degrees C, and smooth tuning of the output frequency over similar to 3 GHz is achieved by smooth tuning of the pump laser. We demonstrate the practicality of the OPO by recording the absorption spectrum of methane near 1649 nm.