Photopolymer is well-recognized as an ideal holographic recording medium, but there is holographic reciprocity law failure in pulse exposure. In this study, the holographic properties of the samples containing an acrylate dendritic monomer with high refractive index (DM-1, n=1.634) are investigated under a 532 nm single-pulse or multi-pulses exposure. The effects of pulse number, spatial frequency, thickness and exposure dosage on diffraction efficiency are discussed. The diffraction efficiency of recorded grating in a sample containing 4% DM-1 (0.5 mm thickness) reaches 77.2% under the 100 pulses exposure. Besides, a grating with diffraction efficiency of 1.35% and narrow selection angle of 0.11° can be recorded in this sample under a single-pulse exposure (8.7 mJ/cm2 exposure dosage), indicating its’ potential in ultrafast holography.
The problem of particle field diagnosing using holography can be met in many areas. But single frame hologram can only catch one moment of the fast event, which can’t reveal the change process of an unrepeatable fast event. For events in different time-scale, different solution should be used. We did this work to record a laser induced particle field in the time-scale of tens of micron seconds. A laser of pulse sequence mode is applied to provide 10 pulses, the energy and time interval of whom is 150mJ and 1μs. Four pockels cells are employed to pick up the last four pulses for holographic recording, the other pulses are controlled to pre-expose the photopolymer based recording material, which can enhance photosensitivity of the photopolymer during the moment of holographic recording. The angular multiplexing technique and volume holography is accepted to avoid shifting the photopolymer between each shot. Another Q-switch YAG laser (pulse energy 100mJ, pulse width 10ns) is applied to produce the fast event. As a result, we successfully caught the motion process of the laser induced particle field. The time interval of each frame is 1μs, the angular range of the four references is 14°, and the diffraction efficiency of each hologram is less than 2%. After a basic analysis, this optical system could catch more holograms through a compact design.
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