Optical microscopy imaging and image-analysis issues in laser cleaning

In earlier work we characterised single-pulse laser cleaning of medium-density (areal coverage 10–20%) alumina particles from glass surfaces with three different lasers. The method of measuring particle-removal efficiency involves optical microscopy imaging (digital) and subsequent image analysis of the area covered by, and/or the number of, particles before and after the single-pulse laser cleaning treatment. The sample-preparation technique used leads to both single particles and agglomerates on the surface. The issues of depth of focus in the imaging and grey-scale thresholding in the image analysis of such samples, with a range of particle and agglomerate sizes, has been systematically investigated. A protocol for optimum imaging and illumination of such samples is described herein. It has been developed based on the results of a systematic investigation of the effect of the image focal plane position relative to the surface also described herein. The image analysis to quantify the particles on the surface involves a judgement of the best threshold grey-scale level in the image to define the boundary between particles and background substrate. A quantitative appraisal of the impact on the laser cleaning efficiency results of a threshold grey-scale level that is set too high or too low, and how these results compare with those obtained for the best-judgement threshold grey-scale level, has been completed. PACS 81.65.Cf; 42.62.Cf; 42.70.Ce     

Characteristics of copper HyBrID-type lasers which use HCl reactive gas

We have investigated the output behaviour of a low temperature HyBrID-type copper laser operating with a flowing Ne–HCl reactive gas mixture. 15.5 W of average power was observed from a 19 mm bore device at 23 kHz PRF corresponding to a specific output power of 78 mW/cm3. The output power was 20–30% lower than that of the same device operating with an Ne–HBr mixture; however, it markedly exceeds the output of similar sized elemental copper vapour lasers (with or without hydrogen additive). This revised version was published online in June 2006 with corrections to the Cover Date.     

Optical field dynamics in a wavelength-versatile, all-solid-state intracavity cascaded pulsed Raman laser

Monitoring the optical field energies in an intracavity cascaded crystalline pulsed Raman laser enables us to probe the dynamics and optimise the performance of the laser, which produces up to 2.1 W average output power at 4 wavelengths between 532 and 636 nm selectable by simple angle tuning.     

Discretely tunable, all-solid-state laser in the green, yellow, and red

We report an all-solid-state intracavity Raman laser with intracavity nonlinear sum-frequency generation providing visible output wavelengths selected from second harmonics and sum frequencies of the fundamental and Stokes fields. The laser comprises a diode end-pumped Nd:YAG laser, an acousto-optic Q switch, a KGd(WO4)2 Raman crystal, and a lithium borate nonlinear converter in a resonator designed to accommodate dynamic thermal lensing. For 20 W of pump power, output powers up to 1.8 W are demonstrated at wavelengths of 532, 555, 579, and 606 nm, selectable by angle and temperature tuning of the nonlinear medium.     

Magnetoelectric effect in cobalt ferrite-barium titanate composites and their electrical properties

CoFe₂O₄-BaTiO₃ composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric conversion factor has been studied as a function of magnetic field.     

Solid-state Raman laser generating discretely tunable ultraviolet between 266 and 320 nm

We report a KGd(WO(4))(2) Raman laser pumped by a 532 nm laser that uses the intracavity nonlinear second harmonic and sum-frequency mixing of the Stokes and fundamental fields in beta-barium borate to generate selectable output among eight output wavelengths over the range 266-320 nm. Output pulse energies of up to 0.22 mJ at 10 Hz pulse repetition rate and average output powers up to 48 mW at 5 kHz were achieved.