D. Dempsey

Spectral-component monitoring and control of pulsed laser deposition of YBCO films

We examine the time-resolved spectral components emitted at approximately 327 nm and approximately 550 nm in YBCO plumes during pulsed laser deposition of thin films using a KrF excimer laser at (lambda) equals 248 nm. The studied emission signals last for approximately 20 microsecond(s) ec, and show variations when process parameters such as laser power, laser excitation voltage, beam focus, chamber pressure, substrate temperature, pulse repetition rate, and target rotation rate are changed. These signals are also dependent on other factors such as target wear and age of the laser gas mixture. Spectral-component monitoring is a supplementary method of real-time plume evaluation, and allows observation of changes both prior to deposition and during the actual deposition. Adjustments can be made to the process parameters to make the plume conform to criteria necessary for the growth of films with specific qualities. The use of these spectral components as real-time process- control state variables for more reproducible fabrication of high quality thin films will be assessed.

Some Optical Properties Of Materials Measured At 1.3 õm

This work surveys the properties of materials at 1.3 um. The interest in this wavelength has been generated by the development of second generation optical fibers and by the development of the iodine (I*) laser, which operates at 1.315 um. Most of the data reported here were taken by Nd:YAG lasers modified to operate at 1.319pm. Spectral scans of some less common materials are presented. The effective optical absorption coefficient Beff measured by laser rate calorimetry is given for all materials. The thermo-optic coefficient an/aT at 1.3 um is given for a number of materials. If 1.3 um results are lacking, values at 1.15 um are given. Among the lower absorbing materials are KCI, LiF, NaCI, CaF2, SiO2, YLF (LiYF4), sapphire (Al203), MgF2, BaF2, and Q-98 phosphate glass. Results on a number of Schott infrared and laser glasses are given, including LG-670, LG-660, LG-750, LG-810, LG-760, LG-680, IRG-7, IRG-9, IRG-3, and IRG-N6. Results are given also on ZnS (normal and water clear), YAG (Y3A1501 2), ZrO2, SrF2, ZnSe, MgO, and CdTe. Some other glasses studied were hafnium fluoride glass, As2S3, CORTRAN 9753 and 9754, and Barr & Stroud calcium aluminate glasses BS 39B and BS 37A. The ten lowest absorbing materials had effective optical absorption coefficients Leff between 0.13 and 0.5 X10-3 cm-1. The lowest a n/aT value measured was 0.06X10-5/°C on Schott LG-660 alkali-Zn-silicate glass.

Photoacoustic and laser rate calorimetry studies of the bulk and surface optical absorption coefficients of laser window materials

Abstract The surface-to-bulk optical absorption ratio, r, was obtained on a group of similar CaF2 samples at 1.3 μm wavelength using three different experimental techniques. Laser rate calorimetry results on a series of samples with varying thickness gave r = β s β B = 0.136 cm . The two slope rate calorimetry technique was applied to a long bar and no second slope was seen. This implies that r is less than 0.3 cm. Analysis of photoacoustic chopping frequency variation studies using the Bennett-Forman theory give r = 0.07 cm about half the multithickness result. Thus all three techniques yielded consistent results.

Investigation of in situ Raman spectra for the control of PLD of YBCO thin film superconductors

Abstract To convert superconducting thin films from an interesting area of research to a viable industrial product such as long length coated-conductors, it is fast becoming apparent that some form of process control with feedback from the growing film is necessary during deposition and post-processing. Several different methodologies are being studied. Of these, one of the most promising is Raman spectroscopy (RS). However, the Raman effect is weak and is typically not well suited as a feedback sensor in the harsh environment of a deposition chamber. RS has been used primarily as an ex situ characterization technique. Two primary questions to be answered are how will the spectra taken during deposition and during post-deposition annealing differ from that of well characterized ex situ spectra. This paper attempts to find a preliminary answer to the second question. In this study, Raman spectra were taken during post oxygen annealing of films under a variety of conditions. The critical transition temperature ( T c ) of films was obtained before and after annealing using AC susceptibility measurements. Results of these tests are used to demonstrate the feasibility of the Raman spectra and images as a feedback mechanism during deposition.

Survey of 1.3 μm Window Materials Continued

The purpose of this work is to screen candidate materials for use in the iodine laser which operates at 1.315 μm. The results presented here are the effective optical absorption coefficient, β e f f , measured by laser rate calorimetry using a Quantronix Nd:YAG laser modified to operate at 1.319 μm. Here we extend the measurements reported last year to new materials. These include MgF 2 , MgO, Kigre Q-98 phosphate glass, YAG (Y 3 Al 5 O 1 2 ), water clear ZnS, CdTe, Schott IRG-N6 CaAl silicate, IRG-7 lead silicate, IRG-9 fluorophosphate glasses, and Hughes HBL glass. Spectral transmission scans using a Beckman 5270 and a Perkin-Elmer 180 spectrophotometer are presented for some of the less common materials. We also take this opportunity to report remeasured absorption values for data reported last year.