Robert Lee Melcher

20‐MHz acoustic waves from pulsed thermoelastic expansions of constrained surfaces

Repetitive pulses from lasers with pulse widths 5–10 nsec or a current generator with 10–25‐nsec widths have been used to launch acoustic waves by thermoelastic expansions. For the laser case, when transparent media such as quartz plates are used to acoustically constrain the energy absorbing surface, an increase of up to 46 dB at 20 MHz was observed over that generated from a free surface. An experiment using a scannable laser to generate elastic waves for flaw detection in a metallic sample is described.

Laser enhanced electroplating and maskless pattern generation

Maskless plating has been achieved through a new technique that utilizes a cw or pulsed laser, focused onto an electrode in an electroplating bath. In the region of optical absorption on the cathode, plating enhancement rates on the order of 103 occur for optical power densities on the order of 104 W/cm2. Laser scanning produces a plating pattern along the scanning path. A qualitative theory based on convective mass transport is used to explain the results.

Calorimetric and acoustic study of ultraviolet laser ablation of polymers

Calorimetric and acoustic studies of the mechanism of pulsed laser ablation of a polymer at the wavelengths of 193, 248, and 308 nm are reported. The results are mutually consistent and provide insight into the ablation mechanism.

Far UV pulsed laser melting of silicon

Calorimetric, acoustic, and morphological studies of silicon irradiated with intense 14‐ns, 193‐nm excimer laser pulses are reported. To within the experimental uncertainty, the entire radiation absorbed is converted to heat at all fluences. The volume changes on melting leads to enhanced acoustic wave generation. The morphology of the surface damage is consistent with the existence of both standing surface acoustic waves and of capillary waves.

A one-megapixel reflective spatial light modulator system for holographic storage

A prototype reflective spatial light modulator (SLM) system has been developed for writing megabit pages of data into a holographic medium at a rate of 12 pages per minute. The SLM is based upon a crystalline-silicon reflective active-matrix array with integrated data drivers, using liquid crystal (LC) electrooptics and a personal computer system with an interface to provide data. The LC has been optimized for high contrast and efficiency with coherent illumination. The resolution-limited contrast was measured at 4:1, which was high enough to provide bit-error-free charge-coupled-device images using modulation and error-correction codes.

Transmission thermal‐wave microscopy with pyroelectric detection

A new form of thermal‐wave microscopy is reported in which the thermal wave transmitted through a sample is detected by a pyroelectric sensor. A thermal image is formed by scanning a point heat source (an electron beam) over the surface of the sample. The image is sensitive only to thermal inhomogeneities in the sample and is independent of the elastic and optical properties of the sample and of the photothermal properties of the surrounding media.

Design and fabrication of a prototype projection data monitor with high information content

A prototype 28-in.-diagonal desktop data monitor capable of displaying 2048 × 2048- pixel images has been designed, built, and evaluated. The monitor uses optical projection technology. A reflective, crystalline silicon active-matrix light valve using liquid crystal electro-optics and a digital electronic interface architecture is described. This rear-projection monitor has four million resolvable pixels, uses three light valves to achieve color, has a low-gain surface diffuser screen, and functions as a fully interactive, color personal computer monitor with motion video capability. The monitor is 20 in. deep.

Thermoacoustic detection of electron paramagnetic resonance

The detection of electron paramagnetic resonance absorption has been achieved using techniques similar to those used in the photoacoustic spectroscopy of solids. Magnetic field and amplitude modulation have been used in both resonant and nonresonant microwave spectrometers.

Noncontact thermal‐wave imaging of subsurface structure with infrared detection

A noncontact thermal imaging system using infrared detection is described. The system uses a chopped and scanned electron beam as a heat source to produce a temperature pattern on the surface of the sample. The resulting thermal radiation is detected and used for numerical image reconstruction of the sample’s subsurface structure.

Pyroelectric detection of magnetic resonance

Magnetic resonance absorption has been detected in paramagnetic and ferromagnetic materials using pyroelectric sensing of the temperature rise of the sample. In addition to being a valuable method for thermal detection of magnetic resonance, the technique provides a useful method for the measurement of the pyroelectric properties of materials.