Colin E. Webb

High-repetition-rate polymeric solid-state dye lasers pumped by a copper-vapor laser

We report on the laser action of pyrromethene 567 incorporated into polymeric matrices and pumped longitudinally with the green line of a copper-vapor laser. When the dye was dissolved in a copolymer of methyl methacrylate and pentaerythritol triacrylate, 290 mW average power at 1 kHz (37% lasing efficiency) was obtained. The laser output decreased to 150 mW after 30 min irradiation time (1.8×106 shots) and to 32 mW after 70 min of operation (4.2×106 shots). Output power of up to 1 W at 6.2 kHz was obtained for short periods of time. Polymeric matrices incorporating rhodamine 6G were also studied.

Influence of cavity configuration on the pulse energy of a high-pressure molecular fluorine laser

We report an investigation of a high-pressure molecular fluorine laser operating at 158 nm. Several cavity configurations were studied, including one employing a roof prism as the high reflector. A maximum VUV pulse energy of 237 mJ, corresponding to a specific output of 3.3 J/1 was obtained when the laser was operated as a double-ended device. With single-ended operation the largest output energy was 176 mJ at a specific output of 2.5 J/1.

530-mW 7-kHz cerium LiCAF laser pumped by the sum-frequency-mixed output of a copper-vapor laser

We report, for what we believe to be the first time, a Ce:LiCAF laser pumped by ultraviolet radiation obtained by sum-frequency mixing of the green and the yellow output from a copper-vapor laser. The 7-kHz pulse repetition frequency free-lasing Ce:LiCAF laser yielded a maximum output power of 530 mW, with a slope efficiency of 32%, from a pump power of 1.9 W. With a single prism tunability from 280.5 to 316 nm was achieved.

Efficient high-power copper-vapor-laser-pumped Ti:Al2O3 laser.

We have demonstrated 5.5 W of average power in the TEM00 mode with a slope efficiency of 30% from a copper-vapor-laser-pumped Ti:Al2O3 laser at a pulse repetition rate of 6.5 kHz and a pump power of 21.4 W. The laser crystal was longitudinally pumped through both end faces. With a three-plate birefringent tuner the laser bandwidth was reduced to less than 0.25 nm and was tunable from 750 to 825 nm.

Kr*2 excimer emission from multi-atmosphere discharges in Kr, Kr-He and Kr-Ne mixtures

The authors present details of the design and performance of a UV pre-ionised transverse discharge device designed for operation at high gas pressures. Stable, arc-free glow discharges could be obtained in pulses of 50-200 ns duration in pure Kr at pressures up to 1.5 bar, and in Kr-Ne mixtures up to 10 bar. Strong emission in the VUV excimer band of Kr*2 in the region 130-160 nm was observed over a wide range of gas pressures, the intensity increasing approximately as the square of the pressure in pure Kr. Attempts to obtain laser action have not been successful to date.

Soft x-ray contact microscopy using laser-generated plasma sources

Of the three main approaches to soft x-ray microscopy currently being investigated (contact, scanning, and direct imaging), we believe that, at present, contact microscopy provides the only solution to the problems of user access to working x-ray microscope systems and radiation damage to biological specimens. A small, transportable, discharge pumped, UV pre- ionized KrF laser system has been developed for the exclusive use of contact microscopy. By employing an injection seeded unstable confocal resonator, a beam of 2.5 times the diffraction limited divergence and energy of the order of magnitude 2 J is generated. By focusing this beam onto the surface of a suitable target material with an intensity of the order of magnitude 1012 W/cm2, a plasma is created which emits largely in the water window region of the spectrum with an efficiency of up to 20%. These x-rays are used to illuminate a biological specimen which is placed in close contact with a photosensitive resist such as polymethyl methacrylate. The specimen may be hydrated and requires no prior preparation such as staining or fixation. A transmission map of the specimen is recorded in the resist within 25 ns, before radiation damage can effect the specimens structure. After chemical development, during which exposed areas of the resist are preferentially dissolved resulting in a relief map of the x-ray transmission of the specimen, the resist is viewed in an SEM or alternatively an atomic force microscope (AFM). Images of various biological specimens are presented.

Measurement of the electron density in a strontium vapour laser

A two-wavelength (10.6 mu m/632.8 nm) Mach-Zehnder interferometer is employed to provide radially and temporally resolved measurements of the electron density in a longitudinally discharge-excited strontium vapour laser over a wide range of operating conditions. From these results it is possible to gain an estimate of both the electron temperature and the Sr2+ ion density.

Resonantly enhanced rare-gas-halide laser frequency up-conversion in Mg vapor.

Frequency up-conversion of XeCl-laser radiation (308 nm) and KrF-laser radiation (249 nm) by two-photon resonantly enhanced four-wave mixing in Mg vapor is reported. A dye laser tuned to two-photon resonance with the 3s-3d(1)D(2) Mg level was used. The dependences of generated signals at 127 and 115 nm on input intensity and number density were investigated. No saturation was observed up to 4 x 10(9) W/cm(2) (249 nm) and 6 x 10(8) W/cm(2) (308 nm). The 115-nm signal was phase matched by using Xe. Conversion efficiencies and signal linewidths are discussed.

Kilohertz pulse repetition frequency slab Ti:sapphire lasers with high average power (10 W)

High-average-power broadband 780-nm slab Ti:sapphire lasers, pumped by a kilohertz pulse repetition frequency copper vapor laser (CVL), were demonstrated. These lasers are designed for damage-free power scaling when pumped by CVLs configured for maximum output power (of order 100 W) but with poor beam quality (M(2) approximately 300). A simple Brewster-angled slab laser side pumped by a CVL produced 10-W average power (1.25-mJ pulses at 8 kHz) with 4.2-ns FWHM pulse duration at an absolute efficiency of 15% (68-W pump power). Thermal lensing in the Brewster slab laser resulted in multitransverse mode output, and pump absorption was limited to 72% by the maximum doping level for commercially available Ti:sapphire (0.25%). A slab laser with a multiply folded zigzag path was therefore designed and implemented that produced high-beam-quality (TEM(00)-mode) output when operated with cryogenic cooling and provided a longer absorption path for the pump. Excessive scattering of the Ti:sapphire beam at the crystal surfaces limited the efficiency of operation for the zigzag laser, but fluorescence diagnostic techniques, gain measurement, and modeling suggest that efficient power extraction (>15 W TEM(00), >23% efficiency) from this laser would be possible for crystals with an optical quality surface polish.

Design and performance of a simple 2 joule KrF laser

We describe the design and performance details of a high-energy KrF excimer laser, operating at 248 nm, suitable for generating laser-produced plasma X-ray sources for applications such as soft X-ray contact microscopy. The UV pre-ionized, discharge excited laser is relatively simple and inexpensive to construct. Using a plane-plane (i.e. Fabry-Perot) cavity arrangement, an output energy of 2.24 J per pulse has been achieved.