10 aJ-level sensing of nanosecond pulse below 10 THz by frequency upconversion detection via DAST crystal: more than a 4 K bolometer

Abstract

By using frequency upconversion detection of terahertz (THz) waves via 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal with an optimized frequency conversion process, ultrahigh sensitivity has been achieved. Direct comparisons with a 4 K bolometer were implemented. By using a simple positive intrinsic negative (PIN) diode without either electrical amplification or optical amplification, frequency upconversion detection can compete with the commercial 4 K bolometer, while by replacing the PIN diode with an avalanche photo diode (APD), it performs more than three orders better than the 4 K bolometer. Based on power calibration, the minimum detectable THz pulse energy is in the order of 10 aJ (9–25 aJ) at 4.3 THz, with a pulse duration of 6 ns. Thus, the minimum number of THz photons that can be detected is down to the order of ${10}^3$ at room temperature. The current THz detection system gives a noise equivalent power (NEP) in the order of $100\mathrm{fW}/{\mathrm{Hz}}^{1/2}$ ($50–128\mathrm{fW}/{\mathrm{Hz}}^{1/2}$). Moreover, by switching current optical detectors, the dynamic range is over six orders.

© 2014 Optical Society of America

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