L. Montgomery Smith

The Fourier Optical Analysis Of Aberrations In Focused Laser Beams

Methods are presented for calculating the radiation intensity in the focal region resulting from the focusing of a laser beam by a spherical surface lens. An approach based upon Fourier optics is employed to include the effects of aberrations as well as diffraction and interference, and digital signal processing techniques are used to speed the calculations. Calculated results are displayed on a digital image processor to aid in visual interpretation. Sample calculations are presented for intensity fields in the transverse and meridional planes of the focal region for circular, gaussian and annular laser beams incident on the lens perpendicularly and at small oblique angles.

Solidification studies using a confocal optical signal processor

The development of a confocal optical processing system and its application to a solidifying metal model are reported. This system has been used to acquire image format data from which quantitative temperature and concentration profiles have been measured. Strong agreement is shown to exist between experimental results obtained in this manner and numerical simulations.

Experimentally acquired meridional-plane intensity distributions of focused light beams in the presence of aberrations

Experimentally acquired images of the intensity distribution in the meridional plane (the plane containing the optical axis) for focused coherent light beams are presented. These images provide a means for studying the effects of aberrations in practical focusing systems. The experimental apparatus for obtaining the data is described, and three example intensity distributions are presented.

Measurement of the accumulation of water ice on optical components in cryogenic vacuum environments

Abstract. Standard vacuum practices mitigate the presence of water vapor and contamination inside cryogenic vacuum chambers. However, anomalies can occur in the facility that can cause the accumulation of amorphous water ice on optics and test articles. Under certain conditions, the amorphous ice on optical components shatters, which leads to a reduction in signal or failure of the component. An experiment was performed to study and measure the deposition of water (H2O) ice on optical surfaces under high-vacuum cryogenic conditions. Water was introduced into a cryogenic vacuum chamber, via a hydrated molecular sieve zeolite, through an effusion cell and impinged upon a quartz-crystal microbalance (QCM) and first-surface gold-plated mirror. A laser and photodiode setup, external to the vacuum chamber, monitored the multiple-beam interference reflectance of the ice-mirror configuration while the QCM measured the mass deposition. Data indicates that water ice, under these conditions, accumulates as a thin film on optical surfaces to thicknesses over 45 microns and can be detected and measured by nonintrusive optical methods which are based upon multiple-beam interference phenomena. The QCM validated the interference measurements. This experiment established proof-of-concept for a miniature system for monitoring ice accumulation within the chamber.

Measuring the Level of Liquid in a Partially-Filled Pipe Via the Ultrasonic Pulse-Echo Method Using Acoustic Modeling

A method for measuring the level of liquid in horizontally oriented pipes was designed, developed and tested. A circuit custom-built for this purpose was used to generate modulated ultrasonic pulses that were applied to a piezo-electric transducer that was used both to launch the acoustic signal and record the returned echoes. The return signal was digitized and transmitted wirelessly to a remote computer for processing where the fluid level measurement consisted of comparing the acquired signal with a simulated signal based upon a model of acoustic wave propagation through the media comprising the set up using cross-correlation with the liquid depth as the free parameter. Laboratory experiments performed with this technique on a steel pipe have shown that it is capable of measuring fluid levels with errors less than 5 mm. Tests on other pipes have been performed, although results were not as accurate. A field test on a pipe in a water tunnel facility successfully determined the presence and absence of liquid in a noisy environment.

Wideband Bessel function chirp signals and their application to the test and evaluation of audio systems

A method is presented for generating a maximally-flat chirp signal whose effective duration is controllable by a single parameter. A sequence of discrete sample values is calculated, each of which is equal to the nth-order Bessel function at a fixed argument. The effective duration of this sequence is approximately twice the value of the argument. Standard analog-to-digital conversion methods can be used to produce a time-varying analog signal for system test and evaluation. The utility of these signals is demonstrated by their application to the spectral analysis of audio systems including multimedia sound cards and a cassette tape recorder.

Acceleration of a Monte Carlo radiation transport code

Execution time for the Integrated TIGER Series (ITS) Monte Carlo radiation transport code has been reduced by careful re‐coding of computationally intensive subroutines. Three test cases for the TIGER (1‐D slab geometry), CYLTRAN (2‐D cylindrical geometry), and ACCEPT (3‐D arbitrary geometry) codes were identified and used to benchmark and profile program execution. Based upon these results, sixteen top time‐consuming subroutines were examined and nine of them modified to accelerate computations with equivalent numerical output to the original. The results obtained via this study indicate that speedup factors of 1.90 for the TIGER code, 1.67 for the CYLTRAN code, and 1.11 for the ACCEPT code are achievable.

Abel inversion using transform techniques

A method is presented for calculating the reconstruction of a circularly symmetric two-dimensional function from its projection, a relation known as the Abel inversion. This technique differs from techniques used previously by using integral transforms for its implementation. The frequency-domain analysis allows for experimentally obtained data, which is often noisy and off-center, to be dealt with in a systematic, rational manner. The formulation of the Abel inversion in terms of transforms, the filtering of the noise, and the estimate of the off-center shift are discussed. Sample calculations of simulated noisy data and the application of the method to an image of a laser sustained plasma are presented.A method is presented for calculating the reconstruction of a circularly symmetric two-dimensional function from its projection, a relation known as the Abel inversion. This technique differs from techniques used previously by using integral transforms for its implementation. The frequency-domain analysis allows for experimentally obtained data, which is often noisy and off-center, to be dealt with in a systematic, rational manner. The formulation of the Abel inversion in terms of transforms, the filtering of the noise, and the estimate of the off-center shift are discussed. Sample calculations of simulated noisy data and the application of the method to an image of a laser sustained plasma are presented.