Angus J. Henderson

Low threshold, singly-resonant CW OPO pumped by an all-fiber pump source

An oscillation threshold of 780mW has been demonstrated in a singly-resonant, continuous-wave optical parametric oscillator (CW SRO) using a fiber-amplified, distributed feedback (DFB) fiber laser as pump source. A linewidth of 1MHz was measured, and the idler frequency was fine-tuned by up to 130GHz by tuning the pump laser. To our knowledge, this is the first example of a single frequency CW SRO pumped by an all-fiber pump source, a reduction in threshold by a factor of three over previous 1- microm-pumped CW SROs, and a reduction by two orders of magnitude in the linewidth of CW SROs pumped by fiber pump sources.

Spectral broadening and stimulated Raman conversion in a continuous-wave optical parametric oscillator

We have confirmed that single-frequency oscillation of a continuous-wave singly resonant optical parametric oscillator is limited to operation below a critical value of the pumping ratio, as predicted by early theoretical treatments. We also report different regimes of spectral broadening as well as stimulated Raman conversion of the signal wave above this critical pump level. We show that spectral broadening may be eliminated by implementing output coupling of the signal wave and demonstrate 8.6 W of total signal and idler output with single-frequency spectra at both wavelengths for 14.5 W of pump power.

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. >

Stable, continuously tunable operation of a diode-pumped doubly resonant optical parametric oscillator.

We demonstrate, for what is the first time to our knowledge, long-term stable, continuously tunable operation of a doubly resonant optical parametric oscillator (OPO) pumped by a single-stripe diode laser without the use of an external semiconductor amplifier. The OPO is based on periodically poled lithium niobate and is pumped by a 150-mW distributed Bragg grating diode laser. 18-mW total output power is generated at 1.3- and 2.3-mum wavelengths. A cavity-length servo system allows continuous signal tuning of 17 GHz and idler tuning of 10 GHz, limited only by the range of a piezoelectric cavity mirror mount. OPO tuning is demonstrated from 1.1 to 1.4 mum and from 2.2 to 3.7 mum.

Continuous-wave parametric oscillation in lithium triborate

We demonstrate a continuous-wave optical parametric oscillator that uses lithium triborate as the nonlinear material in a temperature-tuned noncritical phase-matched type I geometry. Pumped at 514.5 nm, the triply resonant oscillator has a threshold of 50 mW. We obtain peak output powers of 90 mW corresponding to a 10% external conversion efficiency and measure a tuning range of 0.966 to 1.105 μm, limited by the bandwidth of the mirrors. Operating the optical parametric oscillator both at and away from degeneracy, we observe rapid changes in output power as a function of cavity length owing to competition between signal and idler mode pairs.

Broadly tunable LiB3O5 optical parametric oscillator

We report, what is to our knowledge, the first XeCl excimer pumped optical parametric oscillator using critical phase matched LiB3O5 (LBO), to generate broadly tunable coherent radiation with high optical to optical efficiency. Tuning ranges of 355–497 nm in the ultraviolet/blue spectral region, and 809–2.34 μm in the near‐infrared have been obtained, with pump depletions as high as 28%. Oscillation thresholds, external efficiencies, effects of intracavity losses, effects of pump beam size and inherent linewidths (∼0.3 nm) are also reported.

Doubly-resonant optical parametric oscillators: tuning behaviour and stability requirements

By way of a theoretical analysis and demonstration of experimental results, we contrast the influence of type-I and type-II phase-matching on the tuning behaviour and stability requirements of doubly-resonant optical parametric oscillators. Specifically, for near-degenerate operation, we illustrate the advantages of type-II, as opposed to type-I, phase-matching with regard to obtaining single signal and idler mode-pair output. For type-II phase-matching, single cluster and multiple cluster output is shown to depend on the level of pumping and the position of the clusters with respect to the optimum phase-matching condition. Within the experimental type-II phase-matched geometry, we maintain a single signal and idler mode-pair on resonance using a simple cavity length servo-control feedback-loop.

Comparison of lithium triborate and β-barium borate as nonlinear media for optical parametric oscillators

We compare the relative merits of the new nonlinear materials β-barium borate and lithium triborate for use as gain media in singly resonant pulsed optical parametric oscillators pumped by either excimer lasers or frequency-upconverted diode-laser-pumped solid-state lasers. Lithium triborate is the material of choice when one requires low-pump-energy threshold devices ( 100 mJ) that are associated with excimer lasers.

Spectral beam combining of high-power fiber lasers

We have demonstrated spectral beam combining of two high power fiber lasers and obtained more than 40 W output power from the system. The system consists of two 30 W fiber lasers, a diffraction grating and a resonator. Both fiber lasers have broadband fiber Bragg gratings on the rear sides and share the diffraction grating and output coupler on the output sides. The wavelengths of the fiber lasers are determined by the optical dispersion provided by the grating and the collimating lens, as well as the fiber spacing. A model that analyzes dependence of laser line-width on beam quality of an SBC system is given in this paper. We also model a novel configuration that can significantly improve beam quality. The experimental results have shown that control of fiber laser line-width is the key to achieving high power SBC lasers. In addition, a new approach using three gratings is proposed and has been proven by the experiment. The new approach consists of three gratings, in which one grating is used by the SBC cavity to lock wavelengths while the other two combine the collimated beams without beam quality reduction. This approach has successfully improved beam quality M2 from 11 to 2.0.

Continuous frequency tuning of a cw optical parametric oscillator through tuning of its pump source

We report smooth and continuous tuning of the single-frequency output from a continuous-wave, doubly resonant optical parametric oscillator (OPO) based on potassium titanyl phosphate. The device is configured as a single cavity and is pumped by the second harmonic of a diode-pumped Nd:YLF laser. By simultaneously controlling the cavity length of the OPO and the frequency of the pump laser, we could scan the output frequency of the OPO over a range of 4.5 GHz.