From Event: SPIE Organic Photonics + Electronics, 2016
We measured the diffraction efficiency response of two photorefractive polymer devices according to the duration of the single laser pulse used to record the hologram. The pulse duration was varied from 6 nanoseconds to 1 second, while the pulse energy density was maintained constant at 30 mJ/cm2. This changed the peak power from 5 ×109 mW to 30 mW. We observed a strong reciprocity failure of the efficiency according to the pulse duration, with a reduction as large as a factor 35 between 1 second and 30 μs pulse duration. At even lower pulse duration (< 30 μs), the efficiency leveled out and remained constant down to the nanosecond exposure time. The same behavior was observed for samples composed of the same material but with and without buffer layers deposited on the electrodes, and different voltages applied during the holographic recording. We explained these experimental results based on the charge transport mechanism involved in the photorefractive process. The plateau is attributed to the single excitation of the charge carriers by short pulses (τp < 30 μs). The increase of efficiency for longer pulse duration (τp > 30 μs) is explained by multiple excitations of the charge carriers that allows longer distance to be traveled from the excitation sites. This longer separation distance between the carriers increases the amplitude of the space-charge field, and improves the index modulation. The understanding of the response of the diffraction efficiency according to the pulse duration is particularly important for the optimization of photorefractive materials to be used at high refresh rate such as in videorate 3D display.
Pierre-Alexandre Blanche, Brittany Lynn, Robert A. Norwood, and Nasser Peyghambarian, "Mechanisms for the reciprocity failure in photorefractive polymers," Proc. SPIE 9939, Light Manipulating Organic Materials and Devices III, 99390J (Presented at SPIE Organic Photonics + Electronics: September 01, 2016; Published: 23 September 2016); https://doi.org/10.1117/12.2239336.
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