I.T. McKinnie

Solid state dye lasers based on 2-hydroxyethyl methacrylate and methyl methacrylate co-polymers

Abstract The laser performance of a range of solid state dye lasers based on rhodamine 590-doped co-polymers of 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) has been investigated. The optimisation of preparation conditions, including polymerisation initiator and solvent for dye delivery is discussed in detail. Laser efficiency is compared for different polymeric hosts and dye concentrations with a range of output couplers, cavity lengths and repetition rates. Passive and dynamic loss have been determined for each host medium. Laser efficiencies of optimised polymers are among the highest reported for rhodamine 590-doped solid state dye lasers under these operating conditions. Highest slope efficiency of 35% and lowest threshold fluence of 0.06 J cm −2 were obtained with dimethyl sulphoxide (DMSO) additive in MPMMA at 10 Hz repetition rate.

A simple, novel method for the preparation of polymer-tetherable, zwitterionic merocyanine NLO-chromophores

A suite of polymer-ready nonlinear optical merocyanines has been synthesised and characterised. The tethering functionality—a vicinal dihydroxypropyl residue—is introduced onto the donor nitrogen of the chromophore precursor without the need for protection/deprotection steps, thereby giving ready access to potentially high Tg condensation polymer systems. An X-ray crystal structure determination on a representative chromophore 5 confirms the largely zwitterionic nature of these systems and experimental measurements of second-order nonlinear response [β(0)], by hyper-Raleigh scattering, indicate that a pyridylidene donor–quinomethide acceptor combination gives rise to the largest nonlinearity.

Simple zwitterionic merocyanines as potential NLO chromophores

A suite of zwitterionic pyridylidene-based merocyanines that contain no interconnecting π-bridge between the donor and acceptor rings has been synthesised and their second-order NLO properties evaluated largely by semi-empirical computational methods (MOPAC 97/AM1). Contrary to expectation, increasing the degree of inter-ring twist (θ), at least up to 55°, in these new pyridylideneazolone chromophores is found to have little or no effect on the figure of merit [μβ(0)]. An X-ray crystallographic appraisal of one of these chromophores, 14, reveals however that the twist angle (albeit in the solid state) is greater than that predicted by computation and that all other features are consistent with the highly zwitterionic nature of these systems. In spite of this, a combination of factors—insufficient acceptor strength, insufficient extent of conjugation and perhaps insufficient twist angle, in particular—clearly leads to the low values of the quadratic hyperpolarisabilities. The trade-off between targeting a more modest β from a minimum of π-conjugating framework between D and A (and therefore synthetic expediency) and seeking a moderate-to-high dipole moment has therefore resulted in only low figures of merit for these systems.Calculations performed on a suite of readily accessible, isoelectronic cyanines, in which the acceptor is a stabilised cyclopentadienide carbocycle rather than a heterocycle, have revealed the potential that these systems, exemplified by 27, have as NLO chromophores. Representative polymer-tetherable derivatives of this system have been prepared as have the corresponding TDI-based polyurethanes.

Tunable red-yellow laser based on second harmonic generation of Cr:forsterite in KTP

Abstract A new route a visible tunable solid laser source is explored. Wavelengths between 590 and 670 nm are generated by extra-cavity frequency doubling of tuned and free-running gain-swiched Cr:forsterite lasers in KTP. A peak conversion efficiency of 7% is achieved. Measured angular bandwidths and phase-matching angles are found to be in good agreement with theoretical predictions for KTP. The potential for increased conversion efficiency in the wings of the Cr:forsterite tuning range is discussed.

Single-mode near- and mid-infrared periodically poled lithium niobate optical parametric oscillator

Abstract We report a nanosecond Nd:YAG-pumped optical parametric oscillator (OPO) based on periodically poled lithium niobate whose optical bandwidth has been narrowed to

Efficient, low-threshold collinear and noncollinear beta-barium borate optical parametric oscillators.

The performance of collinear and noncollinear pulsed barium borate optical parametric oscillators with third-harmonic Nd:YAG pumping is analyzed. The effects of tangential phase matching and pump Poynting vector walk-off compensation are shown to enhance noncollinear operation. However, we show that these effects are mutually exclusive for a typeI beta-barium borate optical parametric oscillator and furthermore that tangential phase matching is dominant. The selection of a collinear or a noncollinear configuration is determined by pump divergence and spot size as well as by crystal aperture. With a pump divergence of 4mrad, noncollinear operation is optimal. The highest slope efficiency, 37%, and the lowest threshold, 5mJ, are obtained with nearly perfect tangential phase matching. For a pump divergence of less than 2mrad and a similar spot size, collinear operation gives the lowest threshold, 3.2mJ, and the highest slope efficiency, 33%.

Ti/sup 3+/ ion concentration and Ti:sapphire laser performance

The pulsed and CW laser performance of a range of titanium sapphire laser crystals is reported. Titanium ion concentration in the crystals ranged from 0.07 at.% to 0.25 and 0.41 at.% for some recently developed heavily doped crystals. Values of the crystal figure of merit lay between 30 and 220. Threshold, slope efficiency, tunability, and temporal response are assessed. Comparisons are made with the predictions of a simple rate equation model.

Chromium-doped forsterite: the influence of crystal characteristics on laser performance

A study of the dependence of the gain-switched laser operation of chromium forsterite on crystal parameters is presented. Results are reported for a wide range of chromium (IV) ion concentration: 0.02-0.12 at. % and 12-41 figure of merit, with emphasis on performance of the recently developed material with a dopant level of >0.10 at. %. Threshold and slope efficiency calculations are compared with measured performance for all crystals, with variation of pump polarization and output coupling. With 3% output coupling, the lowest threshold of 1.8 mJ, and highest slope efficiency of 13% were measured for a short, high-dopant-level crystal. With 33% output coupling a slope efficiency of 44% was measured for this crystal. Results demonstrate the considerable potential of short, high-dopant-level crystals for applications such as amplification, diode pumping, and narrow-bandwidth operation.

Noncollinear phase matching in a type I barium borate optical parametric oscillator

Abstract A full characterisation of noncollinear type I phase matching is presented for BaB 2 O 4 OPOs pumped at 532 nm. We demonstrate how increased noncollinearity leads to highly efficient low threshold oscillators. We consider the effects of noncollinearity on signal linewidth and oscillator tuning, with good agreement being found with a theoretical model.

Efficient single-frequency pulsed periodically poled lithium niobate optical parametric oscillator

Single axial mode oscillation (< 500 MHz bandwidth) of a pulsed Nd:YAG pumped periodically poled lithium niobate optical parametric oscillator has been obtained. A single intracavity etalon was sufficient to produce single frequency operation for operating signal wavelengths between 1.45 and 1.6 μm. The oscillation threshold increase from the free-running case was between 1.5 and 2. 1 times, and pump depletions of 40-60% were measured across the tuning range. Parasitic processes based on optical parametric generation and cascaded oscillation have been minimised.