The output energy and beam divergence of an injection-seeded KrF laser system, operating at 248 nm, were measured for twelve different coupled confocal unstable cavity arrangements, as a function of the relative timing between the slave and master oscillator lasers as well as of the cavity magnification. The output energy was found to be strongly dependent on both the cavity magnification and the time delay, although the beam divergence shows a less sensitive dependence. An optimized output of 2.2 J in 23 ns with a divergence of 38 μrad was achieved, representing a brightness several times larger than any previously reported for a system of this type.

. We observed enhanced efficiency in the machining of copper using a high-repetition-rate (10 kHz) Q-switched Nd:YLF laser. A significant increase of machining efficiency (material removed per unit time) was observed when the speed of lateral translation of the thin copper sheet across the beam focus was decreased. We attribute this increased efficiency to effects caused by pulse adjacency (i.e. partial overlapping) of several pulses at a given point on the target surface. Several mechanisms which might be responsible for the effect are discussed. Similar results were observed in experiments on laser trepanning. The observed increases in ablation rates might lead to improvements in some industrial processes, e.g. laser drilling, cutting and marking.

. A 10-kHz pulse-repetition-frequency dye-laser master-oscillator power amplifier, end-pumped by a copper vapour laser (CVL), is reported. This laser was based on recently available, lightweight and compact CVL and dye laser components. Dye laser tunability was achieved from 592 to 622 nm and, when the oscillator was etalon line-narrowed, up to 1.5 W of single-etalon-mode output was obtained from the amplifier at the 608-nm peak tuning wavelength. By frequency doubling this amplified output in a BBO crystal we obtained up to 225 mW of 5-GHz 308-nm output, which is suitable for the performance of tropospheric hydroxyl radical concentration measurements.

We describe the operation of an all solid-state pulsed dye laser of high repetition rate (10 kHz) pumped by a diode-pumped laser. Three different active media in the form of coin-sized disks were investigated: the dye rhodamine 6G doped in a copolymer of methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) [Rh6G/P(MMA:HEMA)], and the dye pyrromethene 567 (PM567) doped in copolymers of MMA with pentaerythritol triacrylate (PETA) and with pentaerythritol tetraacrylate (PETRA) [PM567/P(MMA:PETA) and PM567/P(MMA:PETRA)]. Pump radiation at 527nm was provided by a frequency-doubled diode-pumped Nd:YLF laser Q-switched at 10 kHz. Laser output was observed with an initial average power of 560 mW for Rh6G in P(MMA:HEMA), and with an initial average power of 430 mW for PM567 in P(MMA:PETRA) and 220 mW for PM567 in P(MMA:PETA). In the case of Rh6G/P(MMA:HEMA), the output decreased to about half the initial value after about 6.6 min (or about 4.0 million shots) due to dye degradation. The device constitutes a tunable, all solid-state, high repetition rate laser system possibly suitable for biomedical and dermatological applications.

A 10-kHz pulse repetition frequency dye laser, end pumped by a Nd:YLF laser, is reported. This laser was tunable from 590 to 655 nm, and up to 2.55 W of output power was obtained at the 609-nm peak tuning wavelength. By inserting an etalon into the dye laser cavity and frequency doubling using a beta-barium borate crystal, we obtained up to 125 mW of 308-nm single-etalon-mode output, which shows potential for the performance of airborne measurements of tropospheric hydroxyl radical concentrations.

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.

Summary form only given. In recent years dye doped polymers wide excellent photostability and high lasing efficiency have been developed in a number of laboratories. These new doped polymers are a low cost alternative to crystalline solid-state lass materials. To date most work has been conducted at relatively low pulse repetition frequencies (PRFs up to 20 Hz). To avoid photobleaching and thermal lensing problems at high pulse repetition rates the polymer sample may be rotated. For example, 10 kHz 3.58 efficient operation of a F2 dye doped in polyurethane acrylate has been reported by Bondar et al. where a copper vapour laser was used as the pump source to give 70 mW output power. We now report high power operation of solid-state dye lasers operating at a pulse repetition rate of 1 kHz.

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.

We report a high average power Ce:LiLuF laser pumped by the second harmonic of the yellow output from a copper vapor laser. This cerium laser yielded up to 380 mW at a pulse repetition frequency of 7 kHz at the peak lasing wavelength of 309.5 nm, with a slope efficiency of 50%. In addition, single prism tunability was obtained from 305.5 to 316 nm and from 322 to 331.8 nm, Preliminary investigation into color center behavior has been performed involving crystal cooling, He-Ne pump probe experiments and antisolarant pumping.

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 CVL's 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.

In this paper we report high power operation of Ce:LiCAF and Ce:LiLuF lasers pumped by a 7 kHz PRF frequency doubled copper vapour laser (CVL). The free-lasing Ce:LiCAF laser yielded up to 530 mW at a wavelength of 288.5 nm when pumped with 1.9 W, with a slope efficiency of 32%. The maximum output power obtained from the untuned Ce:LiLuF laser was 300 mW at a wavelength of 309.5 rim from 1.05 W of pump power, with a slope efficiency of 38%. By means of a single prism tunability was achieved from 280.5 to 316 rim. in the case of the Ce:LiCAF laser and from 305.5 to 316 rim and 323 to 331 nm for the Ce:LiLuF laser.

Operation of copper vapor lasers (CVL's) using on-axis unstable resonators with very high magnifications M is characterized. A single medium-scale device (1-m-long, 25-mm-diameter bore) with M=360 is capable of delivering 10 W of high-beam-quality (HBQ) output with a divergence of less than two times the diffraction limit at a wall-plug efficiency of 0.5%. The enhanced performance is achieved by tailoring the radial profiles of the initial amplified spontaneous emission (ASE) seed and gain, by means of varying the total neon buffer gas pressure, the partial hydrogen (H/sub 2/) content of the buffer gas, and power loading of the laser head. The degree of insulation of the plasma tube is found to be an important design criterium for optimizing the HBQ performance. These results indicate that efficient generation of HBQ output from medium-scale CVL's requires both a high degree of thermal insulation and operation at high buffer gas pressures with ambient H/sub 2/ concentrations of the order of 1%.

Gasdynamical studies on plasma plumes generated during pulsed laser ablation of solid targets continue to be of interest to improve the understanding of the adiabatic expansion of the ablated material into a (rarefied) background gas. For example, experimental reports in the field of pulsed laser deposition including Schlieren imaging, time-of-flight spectroscopy and ion probe measurements have elucidated the dynamic behaviour of plasma plume. In this paper an alternative approach will be taken to study the gasdynamical properties of the plasma plume by measuring the recoil impulse transferred onto the solid target using a ballistic pendulum.

Short pulse lasers have demonstrated their ability to machine a wide variety of materials with micron precision and micron heat affected zones and recast layers. Whilst there are certain intrinsic advantages in the way in which the ultra-short (femtosecond) pulses interact with certain materials, it is not clear that they have any practical advantage over nanosecond pulses. It is possible to produce both high quality and low quality machining results using a wide variety of pulse formats including nanosecond and femtosecond pulses. In many cases high quality results require that the machining conditions and strategy are optimised for that particular application. Whilst comparison of the machining results under similar conditions but different pulse formats is of interest in understanding the mechanism of the material removal, it is the optimised results and practicality of their implementation that are of real interest to industrial users. We propose that for many applications these results with nanosecond pulses are at least equivalent to the results from femtosecond pulses and that the nanosecond laser is more readily implemented in an industrial production environment.Short pulse lasers have demonstrated their ability to machine a wide variety of materials with micron precision and micron heat affected zones and recast layers. Whilst there are certain intrinsic advantages in the way in which the ultra-short (femtosecond) pulses interact with certain materials, it is not clear that they have any practical advantage over nanosecond pulses. It is possible to produce both high quality and low quality machining results using a wide variety of pulse formats including nanosecond and femtosecond pulses. In many cases high quality results require that the machining conditions and strategy are optimised for that particular application. Whilst comparison of the machining results under similar conditions but different pulse formats is of interest in understanding the mechanism of the material removal, it is the optimised results and practicality of their implementation that are of real interest to industrial users. We propose that for many applications these results with nanosecon...

A high power (6.2W) titanium sapphire laser pumped by a high beam quality copper vapour laser (CVL) at 6.2kHz has been demonstrated. The high beam quality copper vapour laser consisted of a small-scale master oscillator and a double-pass power amplifier giving nearly 20 W output with better than 2 times diffraction-limited beam quality. Up to 5.0 W of narrow-band 780nm output was obtained from a ring Ti:sapphire laser when seeded with a 7 mW CW single mode diode laser. Wavelength tuning of an astigmatically compensated Z-cavity Ti:sapphire laser using up to four intracavity Brewster prisms yielded up to 3.3 W output at 920nm, and up to 1.8 W blue output at 460nm when frequency doubled in an intracavity LBO crystal.

Copper vapour laser (CVL) pumped Ti:sapphire lasers have proved to be excellent sources of high repetition rate tunable near infrared radiation. The CVL wavelengths at 511 nm and 578 nm are well matched to the absorption band of Ti:sapphire and CVLs are unique as pump lasers in that they operate at high repetition rate (2-24 kHz) and high average power (up to 500 W in a single unit). With low and medium power CVLs (up to 18 W per crystal face) longitudinally pumped Ti:sapphire lasers have proved to be a robust and efficient, offering excellent beam quality, low threshold (<0.6 W), and slope efficiencies up to 30% giving the highest output power to date of 6.2 W at 6.2 kHz at 780 nm (1).

In recent years there has been considerable progress in the operation of tunable uv solid state lasers based on trivalent cerium doped fluoride crystals, most notably Ce:LiCAF, Ce:LiSAF and Ce:LiLuF. The pump bands for cerium doped fluorides are in the 250-290nm spectral region, thus requiring a deep uv pump laser. Typically frequency quadrupled Nd:YAG lasers are used to pump Ce:LiCAF and Ce:LiSAF, and KrF excimer lasers for pumping Ce:LiLuF. These pump lasers generally only give short pulses (<20 ns) at PRFs of tens of hertz, thus limiting their suitability for pumping high pulse repetition rate cerium lasers. However recently kHz PRF cerium lasers have been developed using a 10ns frequency quadrupled Nd:YVO 4 pump laser [1].

In recent years numerous reports on pulsed laser ablation of metals using various laser sources have fostered the discussion regarding the limitations due to thermal diffusion to produce feature sizes on (sub-)micron scale smaller than the diffusion length. Particularly in the light of novel micromachining applications, the relative benefits of using pulsed nanosecond (ns) lasers in the visible, such as copper vapour lasers and frequency doubled Nd:YAG, versus femtosecond (fs) Ti:Sapphire lasers operating in the infrared, remains debatable.

Laser guide stars (LGS) are required to obtain complete sky coverage for astronomical telescopes incorporating adaptive optics. Resonant scattering of a high power pulsed laser from atomic sodium in the mesosphere is the most promising technique for the production of a LGS. However, due to saturation of the sodium layer, the efficient generation of a bright LGS using pulsed excitation is difficult. We are devising a modular system where the brightness of the LGS can be increased linearly by adding more laser units [1]. A frequency-locked cw dye laser acts as a master oscillator (MO) which is alternately pulsed amplified through an array of dye amplifiers by means of time-multiplexing thus creating a pulse-train. Consequently, the peak power of each pulse does not increase when the average power is scaled to give a larger photon return from the LGS.