Nonresonant absorption coefficient of single-crystal films of polydiacetylene measured by photothermal deflection spectroscopy

Using photothermal deflection spectroscopy we have measured the nonresonant absorption coefficient of poly (bis-p-toluene sulfonate) of 2,4 hexadiyne-1,6 diol (PTS) single-crystal films for the first time. The absorption coefficient continuously decreases from the reported peak value of ∼9×105 cm−1 at 620 nm (exciton band) to ∼100 cm−1 at 700 nm and finally reaches a value of ∼0.30 cm−1 at λ∼1.3 μm for polarization parallel to the chain axis. Above λ∼1050 nm, the absorption coefficient becomes polarization independent. The low nonresonant absorption coefficient as measured is desirable in terms of nonlinear optical device applications of this material.