David W. Coutts

Cerium-doped fluoride lasers

In the 30 years since tunable ultraviolet (UV) lasers based on 5d /spl rarr/ 4f transition of trivalent lanthanides doped into solid-state hosts were first demonstrated, tremendous progress has been made in these unique laser systems. Today, cerium-doped fluoride lasers offer wide tunability (280-333 nm), high efficiency (up to 62%) and narrow-band output. These lasers can also be used for femtosecond pulse amplification in the UV. Cerium lasers represent a logical route to generation of tunable UV in all-solid-state systems. In this paper, we review the current state-of-the-art cerium laser crystal development and cerium laser systems.

Time resolved beam divergence from a copper vapor laser with unstable resonator

The temporal evolution of the far-field intensity distribution (and hence beam divergence) for the output of a CVL operating with both on-axis and off-axis unstable resonators is investigated in detail. The CVL output pulse consists of several temporally resolved components, where each successive component has lower divergence approaching the diffraction limit. A comprehensive model for the divergence of each temporal component from a CVL operating with a variety of unstable resonators is presented. In this model the resonator controls the output divergence by imposing geometric constraints on the propagation of spontaneous emission on repeated round-trips through the unstable resonator equivalent lensguide. Effects of resonator asymmetry and radial gain variations on the far-field intensity distribution (and hence divergence) are evaluated. Experimental measurements of the temporal evolution of output divergence from a CVL operating with both on-axis and off-axis unstable resonators and for a variety of excitation conditions are also presented. For CVL operation at high pulse repetition frequency the ASE at the start of the laser pulse has an annular profile. This annular gain distribution is found to modify the output far-field intensity distribution of the earlier temporal components of the laser pulse. For on-axis unstable resonators these components are found to have annular far-field intensity distributions, whereas for off-axis unstable resonators they have greatly reduced but anisotropic divergence. >

Optimization of line-focusing geometry for efficient nonlinear frequency conversion from copper-vapor lasers

Detailed parametric investigations of line foci for efficient nonlinear frequency conversion of copper-vapor lasers are presented. For a single medium-scale copper-vapor laser (nominally 20 W), the optimum focal geometry for efficient second-harmonic and sum-frequency generation in BBO is to focus a 3.75-mm-diameter beam into the crystal with an f=60 mm cylindrical lens, Using such a focal geometry, UV powers of up to 1.75 W (SHG of the green), 1.2 W (SHG yellow), and 1.5 W (SFG) have been produced with peak instantaneous conversion efficiency of up to 48%. Conversion efficiencies are most sensitive to the F-number of the cylindrical focusing, with the optimum F-number being approximately 16, and are relatively insensitive to the width of the focused beam.

One watt average power by second harmonic and sum frequency generation from a single medium scale copper vapor laser

Ultraviolet (UV) powers of over 1 W have been obtained by second harmonic and sum frequency generation from a single medium scale (20 W) copper vapor laser (CVL) using a new focal geometry in which the CVL beam is focused in only one direction to produce a line focus within a BBO crystal. High optical conversion efficiencies, 20 and 30%, are observed for the low divergence ( approximately -10 times the diffraction limit) and diffraction-limited components of the CVL output, respectively. Wall-plug efficiencies for UV generation are up to 0.04%. Efficient frequency conversion has also been demonstrated for CVL operating conditions unsuited to the generation of diffraction limited output. >

Observation of the temporal evolution of transverse coherence in copper vapour lasers

Abstract A wavefront folding Mach-Zehnder interferometer together with a fast gated diode array detector has been used to measure the temporal evolution of transverse coherence during the pulse from a copper vapour laser. The transverse coherence has been found to increase stepwise from a low initial value up to complete transverse coherence at the end of the pulse. The results are found to be in excellent agreement with theoretical predictions.

Production of high average power UV by second-harmonic and sum-frequency generation from copper-vapor lasers

Progress in high average power UV generation by nonlinear frequency conversion of the output of copper-vapor lasers (CVLs) is reviewed. The specific parameters controlling the efficiency of nonlinear frequency conversion using CVLs are highlighted, with CVL beam quality and matching the optical beam delivery system to the characteristics of the nonlinear crystal being identified as the most significant issues. Recent experimental studies of second harmonic generation (SHG) with single-CVL oscillators and CVL oscillator-amplifier systems show that by careful optimization of the CVL pump laser and beam delivery systems, it is now possible to generate multiwatt average powers in the UV with high optical conversion efficiency (up to 35%) and overall electrical efficiency (approaching 0.1%). >

Mode-locked deep ultraviolet Ce:LiCAF laser

We report mode-locked operation of a synchronously pumped Ce:LiCAF oscillator. The laser operated in the deep UV with output radiation centered at 291 nm and a pulse duration of 6 ps. The maximum output power measured was 52 mW, with 13% slope efficiency. The Ce:LiCAF crystal has a gain bandwidth capable of supporting few-femtosecond pulses, and so our results demonstrate the potential to form a new class of ultrafast lasers operating directly at deep UV wavelengths.

All-solid-state parametric Raman anti-Stokes laser at 508 nm

We report a parametric anti-Stokes Raman laser using potassium gadolinium tungstate, generating output chiefly at the first anti-Stokes at 508 nm. The compact 4.5 cm long device is pumped by a Q-switched 532 nm laser and uses an off-axis Stokes resonator to provide non-collinear phase matching between the pump and the generated Stokes and anti-Stokes fields. Anti-Stokes output energies up 0.27 mJ were obtained at a conversion efficiency from the pump of 0.46%. Second- and third-order anti-Stokes lines at 486 nm and 465 nm were also observed.

Formation of output in copper vapor lasers

Detailed mechanisms that control the formation of output from copper vapor laser (CVL) oscillators are investigated. Measurements of the spatial and temporal evolution of gain in a CVL amplifier and a CVL oscillator show that a short period of high gain that occurs at the beginning of the inversion period is the dominant feature. This leads to the formation of a burst of amplified spontaneous emission (ASE), whose subsequent propagation and amplification leads to all observable CVL output. The spatial characteristics of this initial burst of ASE are shown to be strongly dependent on the operating conditions of the laser. The implications of this description of CVL output for the design of unstable resonators and oscillator-amplifier systems is discussed.

Increased efficiency of high-beam quality extraction from a copper vapor laser with H/sub 2/-Ne admixtures

We report results of a detailed study investigating the effects of hydrogen additive on the generation of high-beam quality output from a copper vapor laser. Increases up to 390% were observed for the power extracted in the high-beam quality component of laser output, however, the power of the low beam quality output remained relatively unchanged. We attribute these results to modification of the spatio-temporal characteristics of the laser gain with added H/sub 2/. >