Superconducting THz Transmission Spectrometer Comprising Josephson Oscillator and Cold-Electron Bolometer

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Title
Superconducting THz Transmission Spectrometer
Comprising Josephson Oscillator and Cold-Electron
Bolometer M.Tarasov, L.Kuzmin, E.Stepantsov,
I.Agulo, A.Kalabukhov, T.Claeson
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Outline

• Cold electron bolometer concept
• Bolometer samples
• Josephson oscillators
• Experimental setup
• Terahertz response
• Josephson and thermal radiation
• Conclusion

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CEB chip layout

• 4 junction structure for cooling/heating
• Log-periodic antenna for 0.2-2 THz range
• Double-dipole antenna for 600 GHz
• Double-dipole antenna for 300 GHz

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Center part of LPA
Logperiodic antenna designed for frequency range
0.2-2THz . Absorber length is 10mm
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LPA SEM image
Double dipole antenna designed for 300 GHz
central frequency
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SEM view of the LPA center
SINIS bolometer inside the double dipole antenna.
Absorbel length is 10 mm
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AFM picture of CEB
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He3 sorption cooler
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Quasioptical schematics
JJ
oscillator
CEB
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Sample holders
Quasioptical sample holders with silicon and
sapphire extended hyperhemisphere lenses and
pogo-pins for contacts
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Back-to-back configuration
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Sample holder
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YBaCuO film on tilted substrate
SPM view of the 250 nm YBaCuO film on 14o tilted
sapphire substrate. Subgrains are elongated in
the a-b plane perpendicular to tilt direction
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Bicrystal Josephson junction
SPM view of the YBaCuO bridge across the
bicrystal grain boundary. Bridge length is 5 mm,
width below 1 mm.
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Josephson chip layout
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IV curve and Shapiro steps
IV curve of Josephson junction at 4.2 K without
radiation (dashed) and under 300 GHz irradiation
when critical current is completely suppressed
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Current and voltage response
Response of a 10 kW bolometer measured at 260 mK
by applying a dc power to external junctions
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Josephson radiation and overheating
Radiation from a 55 W Josephson junction with
Ic10mA and when ctritical current is suppressed
to zero by magnetic field
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Overheating of the Josephson junction
Temperature of the Josephson microbridge Plancks
radiation law , neglecting Tp For our design
frequency 300 GHz and bias range up to 5 mV, it
can be roughly fitted with the approximate
expression
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Log-periodic and double dipole
Response of bolometer with a double-dipole
antenna (black) and a log-periodic antenna (blue)
under rediation from the same Josephson junction
with log-periodic antenna
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Magnetic field influence
Signal from a Josephson junction with Ic400 mA
(black) and suppressed down to 150 mA (blue),
measured by bolometer with a double-dipole
antenna
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Terahertz response
Dependence of bolometer response on the
frequency of the first harmonic of Josephson
oscillations. Last maximum corresponds to 1.7THz.
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Conclusion
We demonstrated the response of a normal metal
cold electron bolometer at frequencies up to 1.7
THz. A voltage response of the bolometer is
4.108 V/W and an amplifier-limited technical
noise equivalent power 1.3.10-17 W/Hz1/2. We
were first to use electrically tunable high
critical temperature Josephson quasioptical
oscillator as a source of radiation in the range
0.2-2 THz. A high critical temperature Josephson
junction operated at temperature about 2 K shows
a IcRn product over 4.5 mV that enables an
oscillation frequency over 2 THz. Combination of
a Terahertz-band Josephson junction and a hot
electron bolometer brings a possibility to
develop a quasioptical cryogenic compact
transmission spectrometer with a resolution of
about 1 GHz. Such cryogenic spectrometer can be
used for low-temperature spectral evaluation of
any cryogenic detector, quasioptical submm wave
grid filter, neutral density filter, absorber,
etc. Cold electron bolometer detected that a
Josephson junction is overheated by a transport
current even when it is placed on millikelvin
stage.
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Per aspera ad astra