A.J. Kemp

Polarization effects, birefringent filtering, and single-frequency operation in lasers containing a birefringent gain crystal

The effect of having a birefringent gain crystal is studied in the context of two laser systems: an intracavity frequency-doubled microchip laser and a compact single-frequency laser utilizing a birefringent filter. A model based on Jones calculus is proposed to predict the polarization and wavelength structure of the longitudinal modes and is found to be consistent with experimental measurements. The optimization of these systems is discussed, and the importance of the birefringences in the cavity and cavity length is indicated.

Self-Q-switched Nd:YVO4 microchip lasers.

We have observed giant pulses from cw pumped, monolithic Nd:YVO(4) microchip lasers, several hundred times the cw level, with pulse lengths less than 2 ns, which cannot be accounted for by conventional gain switching. These pulses occur as the second longitudinal mode starts to oscillate and can be described by the inclusion of gain-related effects in the formation of a stable cavity.

Compact and highly efficient ultrafast blue light sources: bulk and waveguide approaches to the single pass frequency doubling of femtosecond Cr:LiSAF lasers

We present highly-efficient femtosecond blue light generation from a very simple, compact and potentially robust source. Complementary results from a periodically-poled waveguide suggest that this technique may allow the flexibility of quasi-phasematching in both the spectral and temporal domains to be exploited using compact and efficient femtosecond lasers.

Efficient, high-repetition rate, blue source using a compact Cr:LiSAF laser

Summary form only given. We report a compact, directly diode-pumped Cr:LiSAF laser as an alternative pump source. This laser has an electrical-to-optical efficiency in excess of 1% and produces transform-limited pulses of /spl sim/150 fs in duration at /spl sim/865 nm. The average power is 35 mW and the repetition rate is /spl sim/250 MHz, which implies modest peak powers of less than 1 kW. At these low power levels, efficient frequency doubling usually requires complex arrangements, especially if the pulse duration is to be preserved. In this paper we describe the use of a relatively thick doubling crystal in a single-pass, extra-cavity arrangement. Although the second harmonic pulses suffer temporal broadening, this represents an effective way to achieve efficient frequency conversion in a simplified configuration. The nonlinear crystal was potassium niobate (KNbO/sub 3/) cut for non-critical phase matching at 860 nm and 22/spl deg/C.

The effect of gain crystal temperature on a miniature single frequency Nd:YVO/sub 4/ laser

Summary form only given. Microchip lasers represent highly efficient sources of laser radiation and are easily mass produced at low cost. However, it is difficult to operate them on a single frequency at output powers greater than about 150 mW. Hence, laser geometries that maintain the simplicity exhibited by microchip lasers yet which can be operated on a single frequency at higher output powers are of great interest. In the paper we demonstrate the potential of a birefringent filter, consisting of a Brewster plate and a birefringent crystal, as a frequency selective element in a micro-laser which has additionally, a birefringent gain crystal. Single frequency output powers greater than 760 mW have been obtained at 1064 nm for 2 W of diode laser pump power.

Comparison between Nd:YAG and Nd:YVO/sub 4/ as gain media for a single-frequency micro-laser

Summary form only given. Microchip lasers are highly efficient and easily mass produced sources of laser radiation. Single-frequency operation, however, is difficult at output powers about 150 mW. Thus, there is great interest in developing single-frequency sources that keep the simplicity of microchip lasers yet which can be operated on a single mode at higher output powers. We have demonstrated 760 mW single frequency at 1064 nm under pumping from a 2 W diode laser. This laser employed Nd:YVO/sub 4/, as a gain medium as opposed to Nd:YAG, which has often been used in such lasers in the past. It utilized a birefringent filter consisting of a Brewster plate and a YVO/sub 4/ birefringent crystal.

Guiding effects in microchip lasers at pump powers well above threshold

Summary form only given. Microchip lasers are monolithic devices, typically consisting of a sub-millimetre thick slice of solid state gain material, which is polished to give plane parallel surfaces on to which dielectric mirrors are coated. These lasers are longitudinally pumped by a laser diode. Devices such as Nd:YVO/sub 4/ microchip lasers are highly-efficient and compact lasers which produce beams of high spatial and spectral quality.

V:YAG as passive Q-switch at 1342 nm and 1064 nm

We report the first use of V:YAG as a passive Q-switch for a diode pumped Nd/sup 3+/ laser at 1 /spl mu/m and 1.3 /spl mu/m. Previous investigations of the dynamics of the excited states and saturation of V:YAG showed that this crystal can be successfully used as a saturable absorber for pulsed lasers operating in the red and infrared spectral regions.

Self-Q-switched Nd:YVO/sub 4/ microchip lasers

Microchip lasers are typically formed by applying dielectric mirrors directly to two near-parallel surfaces of a thin slice of laser gain material. Nd:YVO/sub 4/ is a commonly used gain material because of its short absorption depth and high stimulated emission cross section. While working on gain-switched Nd:YVO/sub 4/ microchip lasers, we observed in these monolithic devices large spiking behavior, which could not be accounted for by normal gain-switching theory. Gain switching can produce peak powers in excess of a watt, several times the cw level, with pulses as short as 5 ns. However, the large spikes we observed were several hundred times the cw level with peak powers >25 W and pulses as short as 1.85 ns, more similar in nature to Q-switched pulses. We have constructed a simple model to include this effect in determining the stability of a microchip laser. The results of this model are presented in comparison to the observed experimental work, to show how the effects of gain-related cavity stability can cause self-Q-switching in a Nd:YVO/sub 4/ microchip laser.

Comparison of 671/1342 nm generation with 532/1064 nm in Nd: YV04 microchip lasers

sible way. We have obtained efficient intracavity frequency doubling with the Nd3+ groundstate transition in Nd:YAG and Nd:YAlO using the nonlinear crystals LBO, BBO, KNbO,, and LiJO,. Until now, the maximum cw output of 0.5 W at 473 nm was achieved with the combination of Nd:YAG and LiJO, in a folded cavity when pumping with about 20 W of diode laser power. Because of the internal reabsorption losses of the Nd3+-ground-state transition the application of high brightness pump sources like beam-shaped laser diodes is required. For the red spectral region (620-630 nm) we have investigated sum frequency mixing of diode pumped Nd-lasers operating near 1.06 pm and 1.44 pm. In the fundamental mode, both lasers are able to deliver a few watts output power at a pump level of 10 W. A double resonant cavity was constructed with a mixing resonator that consisted of two separate arms for each laser crystal (1.06 p,mand 1.44 p,mNd:YAG) and one shared arm (with the LBO mixing crystal). So far the maximum cwoutput was 210 mW at 10 W pump power of each laser. In addition, we have operated a Pr, Yb-fiber upconversion laser with 1.1 W output power at 635 nm. This device was pumped with 55 W Tksapphire-laser radiation. However, diode pumping of a fiber system with such high intensity seems to be very difficult. Similar arguments apply for upconversion crystalline lasers. All realized lasers have a large potential for minaturization, which is an important feature for commercial applications in laser TV and projection devices. We acknowledge the support of the German government under contract 16SV094 and the support by Daimler Benz AG, Forschung und Technik, Miinchen.