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Applied Optics

Applied Optics


  • Vol. 21, Iss. 9 — May. 1, 1982
  • pp: 1654–1662

Thermooptic-based differential measurements of weak solute absorptions with an interferometer

David A. Cremers and Richard A. Keller  »View Author Affiliations

Applied Optics, Vol. 21, Issue 9, pp. 1654-1662 (1982)

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An interferometric method of measuring small differences between weak optical absorptions of solutions has been developed using the thermooptic effect. To record the small changes in optical path length ∼λ/200 due to heating, it was necessary to stabilize the fringe pattern with respect to slow thermal drift using a galvanometer-driven compensator plate controlled by a closed feedback loop. Fringe shifts from background absorptions were nulled out to better than 1 part in 400, permitting the measurement of differences in absorptions between two solutions that were 1/100th of background. Using laser powers of 100 mW, absorptions ∼5 × 10−6 cm−1 (base e) could be measured with CCl4 solutions.

© 1982 Optical Society of America

Original Manuscript: September 21, 1981
Published: May 1, 1982

David A. Cremers and Richard A. Keller, "Thermooptic-based differential measurements of weak solute absorptions with an interferometer," Appl. Opt. 21, 1654-1662 (1982)

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  1. The absorptivity (α) used here is defined by the equation I = I0 exp(−αl), where l is the path length of the laser beam through the solution.
  2. See, for example, the following articles and references therein: J. R. Whinnery, Acc. Chem. Res. 7, 225 (1974);D. S. Kliger, Acc. Chem. Res. 13, 129 (1980). [CrossRef]
  3. J. Stone, J. Opt. Soc. Am. 62, 327 (1972). [CrossRef]
  4. J. Stone, Appl. Opt. 12, 1828 (1973);A. Hordvik, Appl. Opt. 16, 2827 (1977). [CrossRef] [PubMed]
  5. W. B. Jackson, N. M. Amer, A. C. Boccara, D. Fournier, Appl. Opt. 20, 1333 (1981). [CrossRef] [PubMed]
  6. N. J. Dovichi, J. M. Harris, Anal. Chem. 53, 106 (1981). [CrossRef]
  7. N. J. Dovichi, J. M. Harris, Anal. Chem. 52, 2338 (1980). [CrossRef]
  8. J. P. Gordon, R. C. C. Leite, R. S. Moore, S. P. S. Porto, J. R. Whinnery, J. Appl. Phys. 36, 3 (1965). [CrossRef]
  9. Instruction manual for model 18 benchtop interferometer, Optical Engineering, Santa Rosa, Calif.
  10. The visibility of a fringe pattern is defined to be V = (Imax − Imin)/(Imax + Imin), where Imax and Imin are the intensities at the maxima and minima of the fringe pattern, respectively. The visibility is a maximum (V = 1) when the interfering beams have the same intensities.
  11. Estimates of the fluorescence quantum yield (Φfl) for solutions of I2/CCl4, CoSO4/water, and CoSO4/CH3OH were obtained by comparing the emission intensity from these with that from rhodamine 6G/CH3OH excited with 3.5 mW of the 515-nm Ar-ion laser line. The absorptivity of the solutions was adjusted to 2.8 × 10−4 cm−1. For the value Φfl (rhodamine 6G/CH3OH) = 0.95 our results indicate that Φfl of all three solutions is <0.02, which was the resolution of our comparison method.
  12. R. C. Smith, K. S. Baker, Appl. Opt. 20, 177 (1981). [CrossRef] [PubMed]
  13. This absorptivity was measured by comparing the initial slope of d(LIA signal)/dt obtained with CH3OH in one cell of the interferometer (other cell empty) with the slope obtained from a reference sample (water). For t ≪ tcEq. (4) becomes ΔOPL(t) = (αoPlt)[dno(λ,T)/dT]/(8.4πktc) = (αoPlt)/(2.1πω2ζ), where the solvent parameters other than αo are lumped into ζ. Because the LIA signal ∝ ΔOPL(t), we obtain α(CH3OH) = α(water)[ζd (LIA signal)/dt]CH3OH/[ζd(LIA signal)/dt]water. The absorptivity of water at 515 nm was taken to be 3 × 10−4 cm−1 (see Ref. 12).
  14. This equation is similar to that derived by C. Hu, J. R. Whinnery, Appl. Opt. 12, 72 (1973), except for the ρ2 factor, omitted from the latter, and which must be included.Our equation is obtained by S. A. Akhmanov, D. P. Krindach, A. V. Migulin, A. P. Sukhorukov, R. V. Khokhlov, IEEE J. Quantum Electron. QE-4, 568 (1968), if χ in their Eq. (28) is set equal to k/ρc rather than the thermal conductivity as they state.[See L. Landau, E. M. Liftshitz, Fluid Mechanics (Pergamon, Oxford, 1959), pp. 202–213]. [CrossRef] [PubMed]
  15. A. D. Fisher, C. Warde, Opt. Lett. 4, 131 (1979). [CrossRef] [PubMed]
  16. F. Zernike, J. Opt. Soc. Am. 40, 326 (1950);R. E. Kinzly, Appl. Opt. 6, 137 (1967);L. Sica, Appl. Opt. 12, 2848 (1973). [CrossRef] [PubMed]
  17. M. S. Burberry, J. A. Morrell, A. C. Albrecht, R. L. Swofford, J. Chem. Phys. 70, 5522 (1979). [CrossRef]
  18. For t ≪ tc both the interferometer and thermal lensing responses are proportional to t/tc = 4tk/ρcω2. Hence for a given solvent the difference in the rate of response of the two techniques is determined in part by ω.
  19. R. B. Green, R. A. Keller, G. G. Luther, P. K. Schenck, J. C. Travis, IEEE J. Quantum Electron. QE-13, 63 (1977). [CrossRef]

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