Photothermal behavior of an optical path adhesive used for photonics applications at 1550 nm

A theoretical and experimental study of photothermal behavior in a commercially available optical path adhesive is described. Photothermal effects were examined for cw and pulsed laser radiation (approximately 1 micros) at 1550 nm. A fiber-optic backreflection technique was used to measure the thermo-optic glass transition temperature of the adhesive. This transition temperature was then used to calibrate fiber-optic photothermal blooming and backreflection pump-probe experiments. Simple thermal models predict DT at 300 mW (cw) to be 65 degrees C and 53 degrees C at 100 W (pulsed). Experimental results are in reasonable agreement with theoretical predictions. The characteristic photothermal relaxation time after a 1-mus pulse for optical path adhesives is found to be 166 micros at the end of a fiber where the mode field diameter is 10.5 micron. Photothermally induced temperatures were found to be below the thermal degradation temperature of the adhesive even at powers as high as 1 W (cw) or 100 W (pulse).