Abstract
The development of a single mode fiber-based pulsed laser with variable pulse duration, energy, and repetition rate has enabled the characterization of photorefractive polymer (PRP) in a previously inaccessible regime located between millisecond and microsecond single pulse illumination. With the addition of CW and nanosecond pulse lasers, four wave mixing measurements covering 9 orders of magnitudes in pulse duration are reported. Reciprocity failure of the diffraction efficiency according to the pulse duration for a constant energy density is observed and attributed to multiple excitation, transport and trapping events of the charge carriers. However, for pulses shorter than 30 μs, the efficiency reaches a plateau where an increase in energy density no longer affects the efficiency. This plateau is due to the saturation of the charge generation at high peak power given the limited number of sensitizer sites. The same behavior is observed in two different types of devices composed of the same material but with or without a buffer layer covering one electrode, which confirm the origin of these mechanisms. This new type of measurement is especially important to optimize PRP for applications using short pulse duration.
Highlights
The development of a single mode fiber-based pulsed laser with variable pulse duration, energy, and repetition rate has enabled the characterization of photorefractive polymer (PRP) in a previously inaccessible regime located between millisecond and microsecond single pulse illumination
Single pulse recording of a diffraction grating was monitored with the probe beam and the maximum value is reported according to the pulse duration
Given that the energy density per pulse is kept constant over the measurement for the different traces, we expected to observe no change in the diffraction efficiency
Summary
In this paper we present a new compact laser source with tunable pulse width and a useful energy per pulse for PRP based applications, discuss the dynamic and maximum diffraction efficiency of two PRP systems according to the temporal pulse width of the writing beams spreading 9 orders of magnitude from nanosecond to seconds, and propose a model that explains the observed behavior. This has a minimal effect on the final laser performance. Ratio inside the sample was set to 1:1 (2:1 outside the sample considering the different beam cross-sections and Fresnel reflection), and a delay line ensured that both beam paths have the same length
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