HYPERIAS Consortium Meeting Siegen, February 23, 2016 Summary of activities Frankfurt Hartmut G. Roskos This work is a part of the project sensor towards terahertz funded by the Hessian LOEWE excellence program

Key Points Scientific Work Report D.1.7 (and 3.3) Publication(s) Information Policy Financial Aspects Secondments / Recruitment First I would like to give you an overview about the content of this talk. After a short introduction I will present our obtained results in my two secondment periods and the improvements we achieved. Afterwards I will be shown. At the end I will give an outlook on possible future work.

Focus on interplay Firefly – TeraFET Broadband THz detector: AlGaN/GaN HEMT with bow-tie antenna, fabricated at FBH, Berlin Scientific Work

High-gain/low-bandwidth amplifier Highlight – High detection sensitivity High-gain/low-bandwidth amplifier Good dynamic range and SNR However, these data are for a gate voltage of -2.1 V, where the CW performance is not optimal. What is the reason?  Figure 8: Effect of signal averaging on the SNR and DR for 0.8-THz pulses Scientific Work

All measurements made at full power on the detector Questions arising High-gain/low-bandwidth amplifier Low-gain/high-bandwidth amplifier All measurements made at full power on the detector Good dynamic range and SNR Variation of best operation points:  Hints towards saturation effects and (for low-gain amplifier) capacitive loading effects Scientific Work

Highlights – High detection sensitivity Detector saturation? I = ½·n·0·c0·E02 Electric field E0 of THz pulse: With a peak power P per pulse of P = 10 nJ / 20 ns = 0.5 W and a supposed cross section of the beam focused by the silicon lens of A = 1 mm2 Such a field would easily saturate the detector. Comparison with CW sources where one operates at the limit of saturation: 0.6 THz, 0.5 mW, 1 mm2 Scientific Work

Open issues – The slope mystery Different slopes (signal/power) for the TeraFET and a Golay cell? Indication for a hitherto unknown large-signal regime of Tera-FETs where the signal is proportional to the radiation field instead of its power? Slope in linear regime: -0.5 dB/post-it Slope: -1.0 dB/post-it Figure 14: Detected THz signal (in dB relative to the unattenuated signal) for different frequencies versus number of post-its used to attenuated the THz beam for (a) a TeraFET resp. (b) a Golay cell detector Scientific Work

Deficit – Missing (failed) normalization Idea: To utilize the IR idler radiation for the correction of pulse-to-pulse intensity fluctuations of the THz signal. BUT: No correlation between these found! Scientific Work

Is the beam profile astigmatic? Open issues – The beam-profile question Is the beam profile astigmatic? (The spot radius should have units mm2, not m2) Scientific Work

Open issues – The polarization puzzle Is the Firefly’s THz beam not linearly polarized? Is the TeraFET not polarization-sensitive as expected? Figure 15: (a) Amplitude of the THz signal versus laser frequency for detector orientation angles of 0° and 90° with respect to the laser polarisation for a gate voltage of -1.9 V. Inset: Detector orientation at the 0°-measurement. (b) Gate-voltage dependence for two frequencies at the two detector orientations. Scientific Work

Administrative and management issues Report D.1.7 (and 3.3) Publication(s) Information Policy Financial Aspects Secondments / Recruitment Administrative and management issues