Measurement of the multi-photon absorption and nonlinear refraction spectra in PTS from 800 to 1600 nm


Since the first measurements of large nonlinear optical coefficients in π-electron conjugated systems, such materials have been studied for all-optical applications. Single crystal PTS seems to offer a very large n2. Often, however, associated with a large n2 is strong two photon absorption, which can limit a material's usefulness for all-optical devices. We report the first picosecond pulse, tunable, multi-photon absorption coefficient and nonlinear refraction measurements on single crystal samples of PTS. The complete spectra yield the two photon resonances obtained from near-resonant to off-resonant conditions. The resonant structure, in turn, reveals the locations of the two-photon states and unveils spectral regions where the two-photon figure of merit, T, may be suitable for all-optical switching. The two photon absorption coefficient measurements were conducted using the Z-scan method with two different systems. The measurements using the 65-ps system indicated the presence of a very strong resonance at 900 nm. In addition three more resonances were identified above 1000 nm: at 1200, 1400, and 1550 nm, with the resonance at 1200 nm being strongest. The presence of the two photon state near 1400 nm confirmed the resonance implied from previous third harmonic generation experiments. The locations of the identified, multiphoton states, with respect to the excitonic peak, are shown in Fig. 2. The resonance at 1200 nm indicates a strong two-photon state located slightly above the excitonic peak. The resonances at 1400 nm and 1550 nm represent two weaker states well below the single-photon state. Finally, a nonresonant measurement was performed at 1600 nm which gave a two photon absorption coefficient of no more than 0.2 cm/GW and a n2 = 1.5(±0.3) × 10-12 cm2/W, giving a T of 0.04. The two photon absorption and nonlinear refractive index spectra, particularly when combined via the figure of merit, T, reveal the spectral regions in PTS where all-optical devices may work, as shown in Fig. 3. Near 1350 nm, T approaches 1, indicating a useful region of the spectra. T drops significantly below 1 around 1470 nm and again beyond 1580 nm offering the possibility for all-optical devices in these regions.

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Proceedings of the International Quantum Electronics Conference (IQEC'94)

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Article; Proceedings Paper



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0028572794 (Scopus)

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