John R. Lankard

Excimer laser etching of polyimide

It is reported that thin films of polyimide are efficiently etched in air at pulsed excimer laser wavelengths of 248, 308, and 351 nm. Etch rate versus incident fluence data are found to obey a Beer–Lambert etching relation. Sharp laser fluence thresholds for significant etching are found to correlate with the wavelength‐dependent absorption coefficient. The absorbed energy density required to initiate significant etching is found, within experimental error, to be independent of the wavelengths examined. It is felt that this information demonstrates the predominantly thermal nature of the laser etching mechanism. Additionally, infrared spectroscopy and coupled gas chromatography/mass spectroscopy were used to identify several gases evolved during pulsed laser etching of polyimide in both air and vacuum.

Flashlamp‐Pumped Organic‐Dye Lasers

The results of recent theoretical and experimental studies on flashlamp‐pumped organic‐dye lasers are presented. The importance of rapid pumping is considered in detail. Constructional aspects of a suitable flashlamp assembly are given, and lasing characteristics of various organic dyes excited by this lamp are summarized.

Tunable coherent ir source based upon four‐wave parametric conversion in alkali metal vapors

A new type of near‐ir source producing a coherent output with a spectrally narrow (∼ 0.1 cm−1) and continuously tunable frequency is described. It utilizes a four‐wave mixing process in alkali metal vapor with input beams provided by two nitrogen‐laser‐pumped dye lasers. Tunable output has so far been observed in the range 2–5.4 μ.

Ruby laser Q-switching elements using phthalocyanine molecules in solution

Following the original suggestion of R. W. Hellwarth, 1 many investigators have succeeded in obtaining coherent light from optically pumped solid state lasers in the form of intense, sharp, single pulses. These pulses are commonly referred to as “giant” pulses, in recognition of the fact that their peak intensity far exceeds that of any of the several pulses (“spikes”) which are normally emitted in several-hundred-microsecond bursts when a laser is pumped beyond threshold. The duration of a giant pulse is usually only a few tens of nanoseconds. In contrast, the duration of each spike in the output of a normally operated laser is several hundred nanoseconds.

Pulsed CO2 laser etching of polyimide

Etching of thin polyimide films in air was investigated using a line tunable, pulsed CO2 laser. The threshold fluence for etching at a wavelength of 944 cm−1 (10.6 μm) exceeds that at 1087 cm−1 (9.2 μm) by a factor of 4. This is consistent with the infrared absorption spectrum which shows polyimide to be significantly more absorbing at 1087 cm−1. As a result, etching at 1087 cm−1 produces a cleaner, more precisely defined region. Analysis of the vapors generated during laser etching shows the simple gases CO2, H2O, and CO to be present.

FREQUENCY‐LOCKING OF ORGANIC DYE LASERS TO ATOMIC RESONANCE LINES

Locking of the output of a flashlamp‐pumped Rhodamine 6G dye laser to the D lines of sodium vapor was achieved by means of the large Faraday rotation that occurs in the vicinity of the resonance lines. The laser beam was observed to consist spectrally of two sharp components symmetrically disposed on either side of the D1 and D2 lines. The laser doublet splitting varies with magnetic field.

STIMULATED ELECTRONIC RAMAN SCATTERING

Stimulated electronic Raman scattering in potassium vapor is observed. The primary source was a nitrobenzene Raman‐shifted ruby laser. The secondary beam frequency occurs 58 cm−1 to the high energy side of νp.

Time‐resolved infrared spectral photography: Study of laser‐initiated explosions in HN3

Recent improvements in the technique of time‐resolved infrared spectral photography (TRISP) are described. With this technique CO2 laser‐induced thermal explosions of gas phase HN3/DN3 mixtures were investigated. HCl gas added to the mixtures was utilized to probe the transient temperature of the reaction. An induction period and a phase of rapid energy release were clearly identified and characterized both with respect to temperature and utilization of reactant material.Recent improvements in the technique of time‐resolved infrared spectral photography (TRISP) are described. With this technique CO2 laser‐induced thermal explosions of gas phase HN3/DN3 mixtures were investigated. HCl gas added to the mixtures was utilized to probe the transient temperature of the reaction. An induction period and a phase of rapid energy release were clearly identified and characterized both with respect to temperature and utilization of reactant material.

The application of laser process technology to thin film packaging

Laser process technologies have been developed which are well suited to the manufacture of thin film electronic packages. The authors discuss three technologies-laser ablation, laser-assisted metal etching, and laser chemical vapor deposition-and how they can be used in polymer and metal patterning. Process and tooling considerations as well as specific applications are presented.<<ETX>>

Laser initiated thermal isomerization of methyl isocyanide

Abstract Application of single pulses of CO 2 TEA laser radiation to a vapor of methyl (CH 3 NC), with the laser tuned to coincide with the fundamental frequency v 4 of this molecule, results in more than 50% conversion of the gas to its isomer methyl cyanide (CH 3 CN). The experiments, performed at room temperature at pressures 10–100 torr, are interpreted in terms of laser induced heating which is sufficient to trigger a thermal explosion.