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20 February 2014 Detection of nanoscale defects in optical films by photothermal reflectance microscopy
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We present a photothermal reflectance microscopy for detecting local defects inside optical films. This technique employs CCD-based thermoreflectance microscopy, which measures temperature-dependent optical reflectivity changes of materials. For photothermal imaging, an 808 nm CW laser beam with sinusoidal modulation is used to heat absorbing defects in the transparent optical film. The thermo-optic response resulting from the laser beam absorption of defects in the material yields a periodic alteration in the reflectivity around the defects. Such a time-varying thermoreflectance signal is probed with a 636 nm LED, and the amplitude of this signal is detected using a homodyne lock-in detection scheme, permitting enhancement of the defect contrast. The feasibility of the proposed imaging system is demonstrated on an optical material having absorbing inclusions, showing that the variation of the normalized optical reflections clearly reveals the local distribution of the submicron-sized defects buried in the optical material.
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Ki Soo Chang, Woo June Choi, Dong Uk Kim, and Jun Ki Kim "Detection of nanoscale defects in optical films by photothermal reflectance microscopy", Proc. SPIE 8963, High-Power Laser Materials Processing: Lasers, Beam Delivery, Diagnostics, and Applications III, 896313 (20 February 2014);

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