1. 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

2. 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.

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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

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