Implementation of a Hot Electron
Bolometer (HEB) for THz
Detection
Matthew Kelley, Rogier Braakman, and Geoffrey Blake – Division of Chemistry
and Chemical Engineering, California Institute of Technology
Daniel Santavicca, Matthew Reese, and Daniel Prober – Department of
Applied Physics, Yale University
Ohio State International Symposium on Molecular
Spectroscopy – June 18, 2007
Motivations
• High resolution gas phase THz
spectra are difficult to acquire but
have application to:
– Astronomy
– Chemical Physics
– Atmospheric Chemistry
Applications/Interest
• THz spectroscopy is hard to implement in a lab setting.
• Direct Detector
– Measurement of absorption spectrum with an appropriate light
source.
• As a Heterodyne Mixer (Braakman WI03 2006)
– Hope to replicate the unparalleled success of Flygare’s FT-MW.
Molecular nozzle
mirrors
Wire grid polarizer (R~99%)
THz photomixer
e.g. P,  meter
1.5 m Er doped
fiber Amplifier
50:50 beam splitters
Heterodyne HEB
THz mixer
3 dB coupler
Mirror (R>99.99%)
mirror
Amplifier, filters
Fixed tuned
1.55 m DFB laser
Tunable 1.55 m
Agilent laser
How A HEB Detector Works
• As incoming radiation is absorbed, the
device (Nb Microbridge) heats up and
changes resistance.
• Near the superconducting regime, the
device is most sensitive.
Sensitivity vs. Saturation
• Length and size
determine:
– Bandwidth/Reset speed
– Saturation power
• Two cooling mechanisms
prevail:
– Diffusion cooling (fast)
– Electron-phonon
interaction (slow)
Burke, P. J., Schoelkopf, R. J., Prober, D. E., Skalare, A., Karasik, B.S., Gaidis, M. C., McGrath, W. R.,
Bumble,B., and LeDuc, H. G. Appl. Phys. Lett., 1999, 85, 1644-1653
.
Experimental Setup
• Chopping at 330 Hz
• Hot vs. Cold Load (77 K)
• Optocoupler separates
device from preamp ->
Bias stability improved
Adder Box
Bias Box
5K
IoutGain=500, 1000
10 
Rsense=10 
Iout
VoutGain=500,1K
Vout
Shorting Box
Preamp
Dewar @ 4.2 K
Lock In
HEB
Optical Chopper
Low Pass @ 10 MHz
Noise Performance
Noise Vs. Chopping Frequency
0.16
0.14
Noise (mV*2000)
• Noise is white above
100 Hz.
• Chopping tests give
accurate noise
performance
• S/N ~ 160
0.12
0.1
0.08
0.06
0.04
0.02
0
0
50
100
150
200
250
Frequency (Hz)
300
350
400
Responsivity Calculation
•
•
•
•
•
•
•
•
ΔV=0.7 mV
G=2000
Voltage
V
R

λ~0.10
Power






h
h
Tu=290 K
G  h d   h d 




kT
kT
Tl=77K
e
 e

νl~1 THz
νl~2 THz
R~2 kV/W
u
u
l
l
u
l
Calculated Results from Prober
Group (Yale)
Current Work
• FTS Tests
– Limited by
Signal/Noise (~2.5)
• Switch to 4 Wire
Bias
– Closed loop feedback
• Lowers noise in one
channel
• Adds stability to the
bias point
• Improve Optical
Coupling
FTS Diagram4
4:
Benford, D.J., Kooi, J. W., and Serbyn, E. 1998, Proc. Ninth Intl. Symp. Space Thz. Tech., 405.
Conclusions
• The Nb HEBs presented here are suitable
THz detectors for laboratory environments:
– High sensitivity
– Moderate bandwidth
– Resistant to saturation
• Optical coupling is the key.
– Single mode dipole antenna imposes strict
limits
Acknowledgements
• Caltech:
• Yale:
– Prof. Geoff Blake and
group:
– Prof. Dan Prober and
group:
• Rogier Braakman
• Matthew Reese
• Daniel Santavicca
– Prof. Jonas Zmuidzinas
and group:
•
•
•
•
Dave Miller
Tasos Vayonakis
Chip Sumner
Frank Rice
– Prof. Charlie
Schmuttenmaer
• Funding:
– NASA
– NSF
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