Abstract

The design of a multichannel optical monitor for transmittance measurements of thin-film coatings during deposition is described. The system comprises a light source and one or more spectrum analyzers each incorporating a prism monochromator and a 256-element photodiode array detector. This multiple-channel design, in conjunction with an HP 1000 computer and data acquisition period of 100 ms, enables the coating uniformity to be precisely monitored and controlled. High-system throughput has been achieved with a large numerical aperture (f/1.5), while retaining excellent spectral resolution over the 350–1100-nm wavelength range. Experimental measurements indicate a practical resolution equal to the detector-limited resolution, a wavelength reproducibility of 0.1 nm at 400 nm and 0.6 nm at 700 nm, and a photometric accuracy and precision of ~1 and ±0.3%, respectively. The problem of unequal energy distribution across the spectrum is handled by optical rather than the usual electronic compensation.

© 1986 Optical Society of America

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References

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  1. B. Vidal, A. Fornier, E. Pelletier, “Wideband Optical Monitoring of Nonquarterwave Multilayer Filters,” Appl. Opt. 18, 3851 (1979).
    [PubMed]
  2. B. Vidal, A. Fornier, E. Pelletier, “Optical Monitoring of Nonquarterwave Multilayer Filters,” Appl. Opt. 17, 1038 (1978).
    [CrossRef] [PubMed]
  3. H. A. Macleod, “Monitoring of Optical Coatings,” Appl. Opt. 20, 82 (1981).
    [CrossRef] [PubMed]
  4. J. E. Stewart, W. S. Gallaway, “Diffraction Anomalies in Grating Spectrophotometers,” Appl. Opt. 1, 421 (1962).
    [CrossRef]
  5. H. H. Schlemmer, M. Mächler, “Diode Array Spectrometer: An Optimised Design,” J. Phys. E. 18, 914 (1985).
    [CrossRef]
  6. F. W. Billmeyer, P. J. Alessi, “Assessment of Color Measuring Instruments,” Color Res. Appl. 6, 195 (1981).
    [CrossRef]
  7. D. G. Jones, “Photodiode Array Detectors in UV-VIS Spectroscopy, Part I,” Anal. Chem. 57, 1057A (1985).
  8. Y. Talmi, R. W. Simpson, “Self-Scanned Photodiode Array: a Multichannel Spectrometric Detector,” Appl. Opt. 19, 1401 (1980).
    [CrossRef] [PubMed]
  9. W. J. Smith, Modern Optical Engineering (McGraw-Hill, New York, 1966), p. 42.
  10. Data Sheet on EG&G Reticon C-Series Solid State Line Scanners, Sunnyvale, CA (1976).

1985 (2)

H. H. Schlemmer, M. Mächler, “Diode Array Spectrometer: An Optimised Design,” J. Phys. E. 18, 914 (1985).
[CrossRef]

D. G. Jones, “Photodiode Array Detectors in UV-VIS Spectroscopy, Part I,” Anal. Chem. 57, 1057A (1985).

1981 (2)

F. W. Billmeyer, P. J. Alessi, “Assessment of Color Measuring Instruments,” Color Res. Appl. 6, 195 (1981).
[CrossRef]

H. A. Macleod, “Monitoring of Optical Coatings,” Appl. Opt. 20, 82 (1981).
[CrossRef] [PubMed]

1980 (1)

1979 (1)

1978 (1)

1962 (1)

Alessi, P. J.

F. W. Billmeyer, P. J. Alessi, “Assessment of Color Measuring Instruments,” Color Res. Appl. 6, 195 (1981).
[CrossRef]

Billmeyer, F. W.

F. W. Billmeyer, P. J. Alessi, “Assessment of Color Measuring Instruments,” Color Res. Appl. 6, 195 (1981).
[CrossRef]

Fornier, A.

Gallaway, W. S.

Jones, D. G.

D. G. Jones, “Photodiode Array Detectors in UV-VIS Spectroscopy, Part I,” Anal. Chem. 57, 1057A (1985).

Mächler, M.

H. H. Schlemmer, M. Mächler, “Diode Array Spectrometer: An Optimised Design,” J. Phys. E. 18, 914 (1985).
[CrossRef]

Macleod, H. A.

Pelletier, E.

Schlemmer, H. H.

H. H. Schlemmer, M. Mächler, “Diode Array Spectrometer: An Optimised Design,” J. Phys. E. 18, 914 (1985).
[CrossRef]

Simpson, R. W.

Smith, W. J.

W. J. Smith, Modern Optical Engineering (McGraw-Hill, New York, 1966), p. 42.

Stewart, J. E.

Talmi, Y.

Vidal, B.

Anal. Chem. (1)

D. G. Jones, “Photodiode Array Detectors in UV-VIS Spectroscopy, Part I,” Anal. Chem. 57, 1057A (1985).

Appl. Opt. (5)

Color Res. Appl. (1)

F. W. Billmeyer, P. J. Alessi, “Assessment of Color Measuring Instruments,” Color Res. Appl. 6, 195 (1981).
[CrossRef]

J. Phys. E. (1)

H. H. Schlemmer, M. Mächler, “Diode Array Spectrometer: An Optimised Design,” J. Phys. E. 18, 914 (1985).
[CrossRef]

Other (2)

W. J. Smith, Modern Optical Engineering (McGraw-Hill, New York, 1966), p. 42.

Data Sheet on EG&G Reticon C-Series Solid State Line Scanners, Sunnyvale, CA (1976).

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Figures (11)

Fig. 1
Fig. 1

Relative spectral response for a tungsten–halogen lamp operating at a color temperature of 3100 K (broken line) and a typical quartz-windowed silicon photodiode array (solid line).

Fig. 2
Fig. 2

Experimental setup: L, lamp; SC, source condenser; SH, shutter; IFB, input fiber bundle; MH, measurement head; UWR, unwind roll; TUR, take-up roll; TO, transfer optics; SM, sample; OFB, output fiber bundle; S1, S2, slits; SA, spectrum analyzer; CL, collimating lens; P, prism; FL, focusing lens; PDA, photodiode array detector connected to a HP 1000 minicomputer.

Fig. 3
Fig. 3

(a) Secondary longitudinal chromatic aberration plot; (b) tangential field curvature.

Fig. 4
Fig. 4

Spectrum analyzer.

Fig. 5
Fig. 5

Line spread functions for wavelengths: (a) 365.0 nm; (b) 404.7 nm; (c) 480.0 nm; (d) 706.5 nm; and (e) 1060.0 nm.

Fig. 6
Fig. 6

Transfer optics.

Fig. 7
Fig. 7

Source condenser.

Fig. 8
Fig. 8

Comparison of observed × and predicted ⊙ tangential field for spectrum analyzer. The broken lines denote the range of field positions within 10% of optimal focus.

Fig. 9
Fig. 9

Wavelength calibration curve for one channel of the optical monitor.

Fig. 10
Fig. 10

Semilogarithmic plot of measured system response with (a) 1.5 m ⊡ and (b) 20 m ⊙ long fiber-optic bundles. Inset shows spectral transmission of fibers as a function of length.

Fig. 11
Fig. 11

Modified response with colored glass filter stack in beam. See text for details.

Tables (1)

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Table I Photometric Error ΔT for Nominal 10, 30, and 80 % T Filters

Equations (1)

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T = ( S t - S d ) / ( R t - R d ) ( S 0 - S d ) / ( R 0 - R d ) .

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