Herbert G. Lipson

Infrared characterization of aluminum and hydrogen defect centers in irradiated quartz

As‐received and 60Co‐irradiated cultured quartz is characterized using low‐temperature near‐infrared Fourier spectroscopy, and peaks associated with as‐grown hydroxide (OH) and aluminum hydroxide (Al‐OH) point‐defect centers are measured. Defect‐center distributions are determined from scanning small crystal regions parallel or normal to the crystal‐growth axis. Large variations in point defects are observed arising from variations in substitutional and interstitial impurity concentrations along the crystal‐growth axis. For the initial radiation doses as‐grown OH decreases uniformly across the crystal and forms Al‐OH, but Al‐OH peak strength varies considerably in different crystal sections. This indicates the possibility of radiation‐induced hydrogen diffusion over large distances to compensate nonuniformities in aluminum‐ion distribution. With increasing dose as‐grown OH may stabilize to a constant level in some crystal regions but deplete in other sections. For some crystals, Al‐OH continues to form ev...

Effects of Vacuum Sweeping and Radiation on Defect Distribution in Quartz

Quartz electrodiffused (swept) in an air or vacuum atmosphere, or irradiated with 60Co, is characterized using low temperature infrared Fourier spectroscopy, and peaks associated with as-grown hydroxide and aluminum hydroxide point defect centers are measured. The distribution of hydroxide related defect centers along the z-growth or sweeping axis for high quality quartz is determined from scanning small crystal regions normal to the axis.

Infrared absorption in highly transparent fluorozirconate glass

Detailed measurements of the frequency and temperature dependence of absorption are reported for the highly transparent frequency regime of a promising new infrared glass based on zirconium fluoride. The results are interpreted in terms of intrinsic multiphonon processes.

Residual lattice absorption in semiconducting crystals: frequency and temperature dependence.

Experimental and theoretical investigations of multiphonon absorption in semiconducting solids are conducted. We find that structure persists at lower absorption levels (~10(-2) cm(-1)) and at high temperatures (up to ~550 K) in these materials, in agreement with theoretical predictions. The theoretical analysis indicates that the observed rate of decrease of the absorption with increasing frequency is consistent with available models for the interionic potential and electric moments in these materials. Moreover, the structure in the spectrum is found to be almost exclusively a result of density of states effects, as opposed to k-selection rules.

Characterization of Alkali Impurities in Quartz

Abstract : We report acoustic loss measurements from room temperature to above 500 degrees of C on resonator disks fabricated from high-grade as-grown and swept synthetic quartz, containing both Li(+) and Na(+) alkali impurities. As-grown quartz disks showed an exponential rise of acoustic loss 1/Q with temperature T, starting above 200 degrees of C. Swept samples show the onset of a rise above 400 degrees of C and show high-temperature losses which increase irreversibly with time and are tentatively attributed to the presence of residual alkali. Loss peaks above 300 degrees of C were found in the swept disks. Some of these disappear after exposure to temperatures above 400 degrees of C.

High Temperature Resonance Loss and Infrared Characterization of Quartz

Summary We report the results of electrical resistance at series resonance as a measure of acoustic loss between 150 and 350 OC for resonators fabricated from high grade synthetic and electrolyzed (swept) quartz. An exponential increase of resonator resistance with temperature is observed for all asgrown quartz. This increase is attributed to either lithium or sodium impurity migration. The swept companions of these materials do not show the exponential rise and no essential difference is found between air and vacuum swept material. Strong A1-OH- related bands are observed by infrared spectroscopy in both air and vacuum swept samples. From short-term vacuum sweeping experiments we find that a reduction in as-grown OH--band strengths occurs almost immediately after the onset of sweeping, but the A1-OH- bands do not form until after a few hours of sweeping time. In air swept samples, with hydrogen supplied by the water vapor in the atmosphere, A1-OH- bands appear almost immediately and as-grown OH--bands remain essentially unchanged.

Infrared and Laser Spectroscopic Characterization of Aluminum Defects in Cultured Quartz

Optical absorption at He-Ne and argon laser frequencies has been used to map the distribution of aluminium-hole centres, Al-H/sup +/, in irradiated and vacuum swept quartz. The absorption band associated with Al-h/sup +/ has a strong peak centered at 435 nm and a weaker one at 633 nm. Argon laser lines at 488 and 514.5 nm are close to the wavelength of the stronger peak, while the He-Ne line at 632.8 nm is nearly coincident with that of the weaker peak. Large variations in Al-h/sup +/ absorption for irradiated and vacuum swept crystals correspond to visually observed changes in coloration. The laser method is sensitive and nondestructive, and gives a quantitative measurement adaptable to computerized scanning and recording of data. Measurements of both Al-h/sup +/ and infrared-active aluminium hydroxide centres, Al-OH/sup -/, are used to evaluate the distribution of aluminium-associated defect centres and determine aluminium variations over an entire crystal.<<ETX>>O p t i c a l a h s o r p t i o n a t He-Ne and a r g o n l a s e r f r equenc ie s has been u sed t o map t h e d i s t r i b u t i o n of a l u m i n u m h o l e c e n t e r s , A l h + , i n i r r a d i a t e d a n d vacuum swept c u l t u r e d q u a r t z . A l O f t and as-grown OHd e f e c t d i s t r i b u t i o n s were o h t a i n e d f o r t h e same c r y s t a l r e g i o n f r o m i n f r a r e d a h s o r p t i o n s c a n s . I n t h i s way a l l o f t h e major q u a r t z d e f e c t c e n t e r s w e r e e v a l u a t e d o v e r a n e n t i r e c r y s t a l . The A3 band a s s o c i a t e d w i t h AI-h+ h a s a s t r o n g p e a k c e n t e r e d a t 435 nm and a weaker o n e a t 6 3 3 nrn. Argon l a s e r l i n e s a t 488 and 514.5 nm a r e c l o s e t o t h e w a v e l e n g t h o f t h e s t r o n g e r p e a k w h i l e t h e He-Ye l i n e a t 632.8 nm i s n e a r l y c o i n c i d e n t w i t h t h a t of the weaker peak . L a r g e v a r i a t i o n s in A3 hand a h s o r p t i o n f o r i r r a d i a t e d and vacuum s w e p t c r y s t a l s c o r r e s p o n d t o v i s u a l l y o b s e r v e d c h a n g e s i n c o l o r a t i o n . The l a s e r method is s e n s i t i v e a n d n o n d e s t r u c t i v e a n d g i v e s a more q u a n t i t a t i v e m e a s u r e m e n t t h a n c o l o r a t i o n .

Impurity absorption in CVD ZnSe

Fourier transmission spectroscopic and laser calorimetric measurements have been used to characterize bulk and surface impurity bands in CVD ZnSe. Temperature dependence studies indicate that, while absorption between 1200 cm-(l) and 1800 cm-(1) is mainly from bulk molecular impurities, surface impurities also contribute and introduce a departure from the expected exponential dependence of multiphonon absorption with frequency above 850 cm-(1).

Laser Characteristics of Neodymium‐Doped Lithium Germanate Glass

The spectroscopic characteristics of Nd‐doped lithium germanate glass are compared to those of Nd‐doped silicate glasses; the laser characteristics of Nd‐doped lithium germanate glass are compared to the corresponding properties of Nd‐doped glass and YAG samples. The spectroscopic properties of the Nd‐doped lithium germanate glass are similar in many respects to the familiar Nd‐doped glass materials. The Nd‐doped lasers were end pumped using the 5145‐A output of pulsed argon ion lasers and oscillated at ∼1.06 μ at room temperature. This technique enables a precise determination of the pump energy required to reach the oscillation threshold. Threshold energy, output power, spiking, fluorescent conversion efficiency, laser rod losses, and stimulated emission cross sections at 1.06 μ are compared. Stimulated emission cross‐section values of the Nd:lithium germanate glass obtained by two methods are presented.

Dose dependence of radiation-induced defect changes in quartz

Results are presented on the dose-rate dependence of the principal centers involved in the irradiation process. This investigation covers cultured quartz samples with a range of grown-in OH and aluminum centers. Acoustic loss measurements have been used to determine Al-Na decay, infrared scans to measure local variations in OH decay and Al-OH production, and an optical laser method to determine Al-hole production. Studies at two widely different dose rates show large differences in OH decay and Al-OH production. Curve fitting of these decay and production curves has been used to determine the rate constants involved. Direct evidence of Al-OH and Al-hole defect competition has been obtained from simultaneous measurements of these defects as a function of dose.<<ETX>>