Donald J. Ramsay

Pulsed lasers in particle detection and sizing

We demonstrate the feasibility of using a pulsed copper vapor laser in particle detection and sizing, Despite the low-duty cycle of these lasers (0.025%), the forward scatter of light from 5-microm latex spheres has been detected.

Photon Correlation Spectroscopy of Polydisperse Samples

The method of cumulants for analysing data from polydisperse solutions of scatterers works well for fairly narrow distributions of particle radii. With broader distributions cumulants analysis is less successful, largely because of truncation errors in the series expansions. We have represented continuous broad distributions of decay rates by exponentially spaced δ functions and histogram steps in order to compare these two approaches and to determine an optimal practical procedure. Different histograms, obtained by varying slightly the step positions, are ‘overlaid’ to obtain more detail in the recovered distribution function. Results of this procedure for analysing light-scattering data are presented for both synthetic data of known distribution function and also for real data from a polydisperse suspension of fat particles in milk. For the synthetic data the mean decay rate (and hence the mean particle size), polydispersity and skew of the distribution are recovered more effectively by the histogram me...

Progress in high-speed UV micro-machining with high repetition rate frequency-doubled copper vapour lasers

We report on progress in uv micro-machining with high repetition rate (4.5 kHz) frequency-doubled copper vapour lasers (CVLs). Characteristics of drilling 2 to 300 micron diameter holes in several materials, including polyethylene and polyimide, will be discussed.We report on progress in uv micro-machining with high repetition rate (4.5 kHz) frequency-doubled copper vapour lasers (CVLs). Characteristics of drilling 2 to 300 micron diameter holes in several materials, including polyethylene and polyimide, will be discussed.

The frequency-doubled copper vapour laser - An alternative source for high repetition rate micro-machining

We report on the output characteristics of a high repetition rate, high beam quality UV source, based on a frequency doubled copper vapour laser (CVL), and present preliminary results on the precision drilling of thin polymer films.We report on the output characteristics of a high repetition rate, high beam quality UV source, based on a frequency doubled copper vapour laser (CVL), and present preliminary results on the precision drilling of thin polymer films.

Photon Correlation Spectroscopy of Polydisperse Samples: II. Optimal choice of histogram parameters with exponential sampling

The use of a histogram model of the distribution function of decay rates in the analysis of light-scattering data from polydisperse samples is investigated. Histograms having a wide range of step sizes and number of steps have been fitted to computer-generated data of various polydispersities and noise levels. These histograms have been compared with the original distributions to determine the optimum histogram parameters in each case. The parameter ymax, which determines step size, decreases linearly with increasing ln (noise) but only at about half the rate predicted by the theory of McWhirter and Pike. ymax also decreases with increasing polydispersity. The number of steps is determined, as expected, by the step size and the need for the histogram to span fully that part of the distribution function which contributes to the autocorrelation function at a level above noise.

High-speed precision UV drilling with frequency-doubled copper vapor lasers

The copper vapor laser (CVL) is an efficient, high average power, high pulse rate visible laser, emitting in the green and the yellow. Previous applications of CVLs have been limited to those requiring a high power visible laser source but with no specific need for high output beam quality. Recently we have made substantial progress in understanding the factors that influence CVL beam quality. As a result we are now able to achieve efficient non-linear frequency conversion to produce a number of ultraviolet wavelengths with near- diffraction limited beam quality. The high repetition rate and low divergence uv output of the frequency-doubled CVL makes it an attractive alternative to the excimer laser for a number of applications, including high-speed precision hole-drilling, cutting and scoring in polymers and for deep-uv photolithography. We report here recent developments that have led to efficient generation of uv wavelengths from copper vapor lasers and we demonstrate its potential as a laser source for high-speed precision ultraviolet micromachining.