Nonlinear Transmittance through Laser Protection Barrier: Reverse Photosaturation of 1-Phenylazo 2-Napthalenol in Polymer Host

We have measured the time-dependent transmittance of orange plastic samples composed of the dye 1 -Phenylazo 2-Napthalenol embedded in both polymethyl methacrylate (PMMA) and polycarbonate at various dye concentrations. The spectrophotometric transmittance below 520 nm is measured to be less than O. Ol% for the PMMA samples. However,a 6.4 mm thick PMMA sample containing 0.008% dye concentration reached a steady-state transmittance of 0.5% in 15 seconds for samples irradiated with continuous wave 514.5 nm light at 12 mW/sq cm. The transmittance reached a steady-state of 11% in 2.5 seconds when irradiated with 514.5 nm at greater than 600 W/sq cm incident. This represents a three order of magnitude increase in the transmittance at relatively low irradiance levels. In contrast, a 6.4 mm thick PMMA sample containing a dye concentration of 0.03% continued to transmit less than 0.0 1% with increased irradiance until the material reached damage threshold. We report ground-state absorption curves and transmittance versus time measurements for dye concentrations ranging from 0. 008% to 0. 15% in PMMA and polycarbonate. We compare the steady-state transmittance at 514.5 nm to the incident irradiance. We propose possible mechanisms associated with the nonlinear transmittance characteristics of 1- Phenylazo 2-Napthalenol. Availability: Pub. in SPIE Volume 1864: Solid State Lasers IV, p86-95 1993.