Jan C. Diettrich

Periodically locked continuous-wave cavity ringdown spectroscopy

We demonstrate a simple periodically locked cw cavity ringdown spectroscopy technique that enables a very large number of ringdown events to be rapidly acquired. An external cavity diode laser is locked to a high-finesse cavity, and as many as 16,000 ringdown events per second are obtained by periodically switching off the light entering the high-finesse cavity. Following each ringdown event, the light to the cavity is switched back on and cavity lock is rapidly reacquired. Limited only by our relatively modest digitization rate, we obtained a minimum detectable absorption loss of 4.7 x 10(-9) cm(-1), but we show that faster digitization could provide a sensitivity of 5.9 x 10(-10) cm(-1) Hz(-1/2).

Tunable high-repetition-rate visible solid-state lasers based on intracavity frequency doubling of Cr:forsterite

High-repetition-rate solid-state lasers broadly tunable in the red-orange and infrared spectral regions are reported. Wavelengths between 590 and 670 nm and between 1170 and 1360 nm have been generated by gain-switched Cr:forsterite lasers incorporating intracavity frequency doubling in KTP. Broadband, tuned, and narrow-band systems operating at repetition rates between 1 and 20 kHz have been developed. Maximum visible output power of 40 mW was achieved by frequency doubling of a narrow-band infrared laser, corresponding to a fundamental to second-harmonic conversion efficiency of more than 30%.

Tunable, single axial mode LiF:F2− laser

Abstract We have developed a gain-switched room temperature single axial mode LiF:F 2 − laser using a coupled narrowband resonator. The resonator uses a classic four-prism achromatic beam expander/Littrow grating configuration, augmented with a dichroic mirror that defines a coupled resonator with: (1) reduced threshold and higher efficiency, and (2) dramatically increased axial mode separation for enhanced mode selectivity. One etalon was then sufficient to achieve single axial mode output with MHz bandwidth and an energy conversion efficiency of 5.5%, significantly higher than previously reported for narrowband LiF:F 2 − lasers where only a bandwidth of 300 MHz had been achieved. The single longitudinal mode laser was tunable in single mode between 1120 and 1200 nm. A coupled cavity model was developed to explain the experimentally observed mode structure, and to allow similar coupled resonators to be optimised for other vibronic laser media.

Periodically-poled lithium niobate optical parametric oscillator, pump-tuned by a single axial mode Ti:sapphire laser

We demonstrate a pulsed optical parametric oscillator (OPO) based upon periodically poled lithium niobate, and pumped by a Ti:sapphire laser. Agile and continuous OPO tuning is achieved by tuning the pump laser, with no need for OPO crystal translation or temperature change. The Ti:sapphire laser uses a coupled cavity grazing incidence resonator for efficient, single-axial-mode operation within the OPO spectral acceptance bandwidth. The OPO tuning range is 1200 to 2400 nm, limited only by the available cavity mirrors.

The influence of active ion concentration and crystal parameters on pulsed Cr:YAG laser performance

Abstract An experimental investigation of the effects of crystal characteristics on Cr:YAG laser performance was carried out. Slope efficiency, threshold, and gain-switching parameters are analysed in terms of Cr4+ ion concentration, parasitic loss, and excited state absorption. Laser tuning range and mode structure were examined in each case. Results are compared with the predictions of a rate equation model, which extends a simple gain-switching treatment to include excited state absorption and dynamic pump effects. A best fit to experimental data is used to predict Cr:YAG cross-sections within the wide range of published values. A crystal with low Cr4+ ion concentration gave higher output energy and broader tuning range than more recently developed heavily-doped material.

Novel, single longitudinal mode, near infrared, gain-switched lasers

We have developed a model which allows the behaviour of arbitrary multi-arm coupled gain-switched lasers to be predicted. We have used the model to develop an enhanced Michelson-Fox-Smith resonator for low gain media, as well as a new coupled resonator for higher gain materials.

Dynamics of gain-switched Cr:YAG lasers

An investigation of the influence of pump and laser excited state absorption (ESA), parasitic losses and pump parameters on Cr:YAG laser action has been carried out. A simple rate equation model has been extended to include ESA and dynamic pump effects. Results are compared with those obtained using a full spatio-temporal gain-switching model, and with experimental measurements in three temporal regimes. Comparison allows values for quantum efficiency and laser absorption, emission and ESA cross-sections to be allocated within the wide range of previously published data. Remaining discrepancies are attributed to thermal loading. An optimum pump energy is determined for a given fluence, and effective Cr:YAG energy scaling is demonstrated with only a slight threshold increase. Further enhancement is obtained using 500 ns pump pulses.

2-mJ single-axial-mode gain-switched Cr:forsterite lasers

Single-longitudinal-mode operation of gain-switched Cr4+ laser, with output energy as much as 1.9 mJ, is reported from two different coupled-cavity resonators. A prism-coupled cavity and a modified Michelson interferometric grazing-incidence (MIGI) cavity was pumped by a multilongitudinal-mode Q-switched Nd:YAG laser; the modified MIGI cavity obtained 100-MHz-bandwidth laser output tunable between 1150 and 1330 nm. Conversion efficiency of 3.2% (slope efficiency of 4%) was achieved, with a pump threshold density as small as 0.2 J/cm2. Mode spacing of the laser output in multilongitudinal mode showed increased mode spacing in agreement with a coupled-cavity theory.

Single axial mode, 2 mJ pulses from a gain-switched Cr:forsterite laser

Summary form only given. Single axial mode, pulsed, tunable lasers and OPOs are used in a range of applications in remote sensing and applied spectroscopy. The widely-used grazing incidence configuration has been successfully implemented for single axial mode operation of Ti:sapphire lasers and OPOs. However, efficiencies are typically low with a high pump threshold energy, often close to the damage levels of cavity components. In fact with BBO OPOs and with low gain/high passive loss vibronic laser materials such as Cr:forsterite, similar laser and damage thresholds mean that the grazing incidence cavity is, at best, a marginal approach. Consequently, single axial mode operation of Cr:forsterite has, to our knowledge, only been obtained using a complex cavity with 4-prism beam expander, etalon and diffraction grating. Pump threshold fluence was low (0.3 Jcm/sup -2/), but damage limitations restricted output pulse energy to 300 mJ. We report the design, modeling and single frequency laser performance of two coupled-cavity Cr:forsterite lasers optimized for lower threshold, higher energy operation.

The influence of Cr:YAG crystal characteristics on pulsed laser performance

Cr:YAG offers the best current prospect for tunable solid-state lasers in the 1.3-1.6 micron wavelength region. This range is important for applications in communication, remote sensing, and eyesafe optical ranging.