We have used near IR pump – Mid IR probe techniques to compare the feasibility and potential of using free standing nano-porous and micro-porous silicon (ordered hole arrays) as optically controlled modulators operating in the Mid-Wave Infrared (MWIR) covering the range from 3.3-5 μm. We employed 800 nm pumping pulses with the duration of 60 fs to reduce 4 μm light transmission modulation to about 25% and 45% for both silicon structures, respectively, at excitation powers of 50mW (4 mJ=cm2). However, at 5 μm both structures shown similar contrast of about 60%. The time resolved measurements revealed a fast sub-picosecond rise time for both structures suggesting that the optically generated carriers are a dominant mechanism for the modulation. However, the measurements demonstrated a significant difference in the relaxation dynamics. The nanoporous silicon demonstrated recovery as fast as a few tens of picoseconds and a possibility to effectively work in the GHz regime, while hole arrays shown almost three orders of magnitude slower response making it suitable for the MHz regime.
A. Zakar, S. J. Park, V. Zerova, A. Kaplan, Leigh T. Canham, K. L. Lewis, and C. D. Burgess, "MWIR optical modulation using structured silicon membranes," Proc. SPIE 9992, Emerging Imaging and Sensing Technologies, 999203 (Presented at SPIE Security + Defence: September 28, 2016; Published: 25 October 2016); https://doi.org/10.1117/12.2242287.
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