Abstract

Laser modulated scattering (LMS) is introduced as a tool for defect inspection and characterization of optical materials for high power laser applications. LMS is a scatter sensitive version of the well-known photothermal microscopy techniques. Because only the defects of a super-polished optic generate a scattering signal, the technique is essentially a method for dark-field photothermal microscopy. Experimental results show that the technique (1) measures the local absorption properties of defects, contamination, and laser damage sites; (2) when used in conjunction with DC scattering, can differentiate between absorbing and non-absorbing defects; and (3) detects thermal transport inhomogeneities.

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References

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  1. T. W. Walker, A. H. Guenther, P. Nielsen, "Pulsed laser-induced damage to thin-film optical coatings. II. Theory," IEEE J. Quantum Electron. QE-17, 2053-65 (1981).
    [CrossRef]
  2. S. Papernov, A. W. Schmid, "Localized absorption effects during 351 nm, pulsed laser irradiation of dielectric multilayer thin films," J. Appl. Phys. 82, 5422-32 (1997).
    [CrossRef]
  3. M. F. Koldunov, A. A. Manenkov, I.L. Pokotilo, "Thermoelastic and ablation mechanisms of laser damage to the surfaces of transparent solids," Quantum Electron. 28, 269-73 (1998).
    [CrossRef]
  4. R. J. Tench, R. Chow, M. R. Kozlowski, "Characterization of defect geometries in multilayer optical coatings," J. Vac. Sci. & Technol. A 12, 2808-13, (1994).
    [CrossRef]
  5. S. Papernov, A. W. Schmid, J. Anzelotti, D. Smith, Z. R. Chrzan, "AFM-mapped, nanoscale, absorber-driven laser damage in UV high-reflector multilayers," in Laser-induced damage in optical materials: 1995, H. E. Bennett, A. H. Guenther, M. R. Kozlowski, B. E. Newnam, and M. J. Soileau, ed., Proc. SPIE 2714, 384-94 (1996).
    [CrossRef]
  6. M. A. Paesler, P. J. Moyer, Near-field optics (John Wiley & Sons, Inc., New York, 1996).
  7. P. A. Temple, "Total internal reflection microscopy: a surface inspection technique," Appl. Opt. 20, 2656-64 (1981).
    [CrossRef] [PubMed]
  8. L. Sheehan, M. R. Kozlowski, D. Camp, "Application of total internal reflection microscopy for laser damage studies on fused silica," in Laser-induced damage in optical materials: 1997, G. J. Exarhos, A. H. Guenther, M. R. Kozlowski, and M. J. Soileau, ed., Proc. SPIE 3244, 282-295 (1998).
    [CrossRef]
  9. W. B. Jackson, N. M. Amer, A. C. Boccara, D. Fournier, "Photothermal deflection spectroscopy and detection," Appl. Opt. 20, 1333-44 (1981).
    [CrossRef] [PubMed]
  10. Z. L. Wu, M. Thomsen, P. K. Kuo, C. Stolz, M. R. Kozlowski, "Photothermal characterization of optical thin film coatings," Opt. Eng. 36, 251-262 (1997).
    [CrossRef]
  11. M. Commandre, P. Roche, "Characterization of optical coatings by photothermal deflection," Appl. Opt. 35, 5021-34 (1996).
    [CrossRef] [PubMed]
  12. E. Welsch, D. Ristau, "Photothermal measurements on optical thin films," Appl. Opt. 34, 7239-53 (1995).
    [CrossRef] [PubMed]
  13. B. Woods, M. Yan, J. DeYoreo, M. Kozlowski, H. Radouski, and Z. L. Wu, "Photothermal mapping of defects in the study of bulk damage in KDP," in Laser-induced damage in optical materials: 1997, G. J. Exarhos, A. H. Guenther, M. R. Kozlowski, and M. J. Soileau, ed., Proc. SPIE 3244, 242-48 (1998).
    [CrossRef]
  14. J. Dijon, T. Poiroux, C. Desrumaux, "Nano absorbing centers: a key point in the laser damage of thin films," in Laser-induced damage in optical materials: 1996, H. E. Bennett, A. H. Guenther, M. R. Kozlowski, B. E. Newnam, and M. J. Soileau, ed., Proc. SPIE 2966, 315-25 (1997).
    [CrossRef]
  15. M. D. Feit, J. Campbell, D. Faux, F. Y. Genin, M. R. Kozlowski, A. M. Robenchik, R. Riddle, A. Salleo, J. Yoshiyama, "Modeling of laser-induced surface cracks in silica at 355 nm," in Laser-induced damage in optical materials: 1997, G. J. Exarhos, A. H. Guenther, M. R. Kozlowski, and M. J. Soileau, editors, Proc. SPIE 3244, 350-55 (1998)
    [CrossRef]
  16. Craig F. Bohren and Donald R. Huffman, Absorption and scattering of light by small particle (John Wiley & Sons, New York, 1983).

Other

T. W. Walker, A. H. Guenther, P. Nielsen, "Pulsed laser-induced damage to thin-film optical coatings. II. Theory," IEEE J. Quantum Electron. QE-17, 2053-65 (1981).
[CrossRef]

S. Papernov, A. W. Schmid, "Localized absorption effects during 351 nm, pulsed laser irradiation of dielectric multilayer thin films," J. Appl. Phys. 82, 5422-32 (1997).
[CrossRef]

M. F. Koldunov, A. A. Manenkov, I.L. Pokotilo, "Thermoelastic and ablation mechanisms of laser damage to the surfaces of transparent solids," Quantum Electron. 28, 269-73 (1998).
[CrossRef]

R. J. Tench, R. Chow, M. R. Kozlowski, "Characterization of defect geometries in multilayer optical coatings," J. Vac. Sci. & Technol. A 12, 2808-13, (1994).
[CrossRef]

S. Papernov, A. W. Schmid, J. Anzelotti, D. Smith, Z. R. Chrzan, "AFM-mapped, nanoscale, absorber-driven laser damage in UV high-reflector multilayers," in Laser-induced damage in optical materials: 1995, H. E. Bennett, A. H. Guenther, M. R. Kozlowski, B. E. Newnam, and M. J. Soileau, ed., Proc. SPIE 2714, 384-94 (1996).
[CrossRef]

M. A. Paesler, P. J. Moyer, Near-field optics (John Wiley & Sons, Inc., New York, 1996).

P. A. Temple, "Total internal reflection microscopy: a surface inspection technique," Appl. Opt. 20, 2656-64 (1981).
[CrossRef] [PubMed]

L. Sheehan, M. R. Kozlowski, D. Camp, "Application of total internal reflection microscopy for laser damage studies on fused silica," in Laser-induced damage in optical materials: 1997, G. J. Exarhos, A. H. Guenther, M. R. Kozlowski, and M. J. Soileau, ed., Proc. SPIE 3244, 282-295 (1998).
[CrossRef]

W. B. Jackson, N. M. Amer, A. C. Boccara, D. Fournier, "Photothermal deflection spectroscopy and detection," Appl. Opt. 20, 1333-44 (1981).
[CrossRef] [PubMed]

Z. L. Wu, M. Thomsen, P. K. Kuo, C. Stolz, M. R. Kozlowski, "Photothermal characterization of optical thin film coatings," Opt. Eng. 36, 251-262 (1997).
[CrossRef]

M. Commandre, P. Roche, "Characterization of optical coatings by photothermal deflection," Appl. Opt. 35, 5021-34 (1996).
[CrossRef] [PubMed]

E. Welsch, D. Ristau, "Photothermal measurements on optical thin films," Appl. Opt. 34, 7239-53 (1995).
[CrossRef] [PubMed]

B. Woods, M. Yan, J. DeYoreo, M. Kozlowski, H. Radouski, and Z. L. Wu, "Photothermal mapping of defects in the study of bulk damage in KDP," in Laser-induced damage in optical materials: 1997, G. J. Exarhos, A. H. Guenther, M. R. Kozlowski, and M. J. Soileau, ed., Proc. SPIE 3244, 242-48 (1998).
[CrossRef]

J. Dijon, T. Poiroux, C. Desrumaux, "Nano absorbing centers: a key point in the laser damage of thin films," in Laser-induced damage in optical materials: 1996, H. E. Bennett, A. H. Guenther, M. R. Kozlowski, B. E. Newnam, and M. J. Soileau, ed., Proc. SPIE 2966, 315-25 (1997).
[CrossRef]

M. D. Feit, J. Campbell, D. Faux, F. Y. Genin, M. R. Kozlowski, A. M. Robenchik, R. Riddle, A. Salleo, J. Yoshiyama, "Modeling of laser-induced surface cracks in silica at 355 nm," in Laser-induced damage in optical materials: 1997, G. J. Exarhos, A. H. Guenther, M. R. Kozlowski, and M. J. Soileau, editors, Proc. SPIE 3244, 350-55 (1998)
[CrossRef]

Craig F. Bohren and Donald R. Huffman, Absorption and scattering of light by small particle (John Wiley & Sons, New York, 1983).

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Figures (7)

Fig. 1.
Fig. 1.

Illustration of the principle of laser modulated scattering (LMS): (a). DC scattering from a defect; (b). An amplitude-modulated pump laser beam is used to generate laser LMS.

Fig. 2.
Fig. 2.

LMS signal as a function of the pump laser power. The sample used is a defect on the surface of laser glass. Experimental parameters: pump laser - wavelength 488 nm, beam size ~100μm, normal incidence, chopping frequency 70 Hz; Probe beam - wavelength 633 nm, beam size ~100 μm, 45° incident angle; Detector - pinhole size ϕ1.0 mm, 7.5 cm from the heating spot and 60° from the normal of the sample, detecting forward scattering of the probe beam from the reflection mode as shown in Figure 1(b).

Fig. 3.
Fig. 3.

Defect mapping using (a) LMS and (b) DC scattering of the same area of an optical coating. The color scale is in arbitrary units. The laser parameters are as follows: pump wavelength 1.06 μm; probe wavelength 0.6328 μm; pump beam size ~ 5 μm; probe beam size ~ 25 μm. Other parameters are the same as shown in Figure 2.

Fig. 4.
Fig. 4.

Profile of defect D shown in Figure 3. Compared with the background material, the DC scattering of the defect is only 2.8% higher but the LMS signal is about 10 times higher.

Fig. 5.
Fig. 5.

LMS image (top) and profile (bottom) for a laser damage site of an optical coating sample. The defect labeled as C is laser-induced debris. The experimental parameters are the same as shown in Figure 3.

Fig. 6.
Fig. 6.

High resolution DPTM image of the laser induced debris as labeled as C in Figure 5. Both the amplitude and the phase image indicate that the debris consists of two separate parts, i.e. A and B; profiles of them are shown in Figure 7.

Fig. 7.
Fig. 7.

Profiles of Section A and B of the debris as shown in Figure 6. While for both sections the absorption peaks at the center, part A and B defers in that A is more symmetric than B.

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