Far-infrared intensity interferometry
for future space mission
Hiroshi Matsuo
Advanced Technology Center
National Astronomical Observatory of Japan

Contents⚫ High angular resolution Far-IR observations⚫ HBT intensity interferometry⚫ Imaging technique⚫ Merit of direct detectors⚫ Possible future programs

MACS1149-JD1
z=9.11 by [OIII] 88 mm (3.4 THz)

Hashimoto et al., Nature (2018)

Strong [OIII]88um from a Quasar (z=6.04)

Hashimoto et al. PASJ (2019)

Atmospheric Windows from Atacama（alt. 4800m）
1mm500um

300um

200um
z = 9.11

Matsushita, Matsuo et al. PASJ (1999)OIII 88um

Angular Scale of Observation
All Sky3°10″

THz
Gap10 mas

10 mas

910111213
Log Frequency [Hz]14

Far-Infrared
Intensity Interferometry
Credit: EHT Collaboration⚫ Closer to the central activities !

ALMA (ESO/NAOJ/NRAO), Imanishi et al.
Inoue, Tamura, Matsuo et al. (2016)

Credit: ALMA (ESO/NAOJ/NRAO)

Credit: ALMA/NAOJ

Narrabri Stellar Intensity Interferometer

AT N F D a i l y As t r o n o m y
17th of August 2015

PictureHanbury-Brown and Twiss
Experiment (1956)

HBT Intensity Interferometry⚫ Correlate “Intensities”

from two individual telescopes⚫ Radio intensity interferometer at 125 MHz– Hanbury-Brown et al. (1952)⚫ Optical interferometer– Hanbury-Brown and Twiss (1956)

from Hanbury-Brown (1974)“The Intensity Interferometer”

Limitation of intensity interferometers⚫ High Dynamic Range is required– Intensity correlation ∝ (Amplitude correlation)2⚫ Low efficiency for optical observations– Observation of very early type stars only

⚫ Phase information is missing– Measurement of stellar diameters only

Photon Bunching, Anti-bunching
2nd order correlation function

From M. Fox
Quantum Optics (2006)

Fluctuation of thermal radiation12n = n + n , where n =eh kT−1n : photon occupation numberA = 2

NEP = 2 P  (h + kTB ) [ WReferences

A. Einstein (1909)
J. Mather (1984)
J.M. Lamarre (1986)
J. Zmuidzinas (2003)

Hz ]T=TB / √Bt

Photon bunchingTHz photon fluctuation
10 cm

kT 1 nWh 1 nW

250 K

h 10 pW

2.5 K

B = 100 GHz

10 mm

1 mm

kT 10 pW

Long Baseline Intensity
Interferometry

RecorderB > 1GHzRecorderB > 1GHz

Calculate correlation and delay

Photon Bunches fordelay time measurements⚫ Photon bunch can be a measure of delay time.
– Complex visibility can be obtained.

⚫ Large number of THz photon is expected.

100 M photons/sec from Stars and AGNs
1 Jy at 1 THz (B=100 GHz), using f10 m telescopet = 10-13 sec in 100 sec is expected.
𝛥𝑡 =THz Photons are bunched !

1𝑁 𝑁∙𝜏

N: photon ratet : integration time

Nobeyama Radioheliograph (NoRH)• Interferometer exclusively observing the Sun• 84 antennas of 80 cm diameter• 17 GHz R+L / 34 GHz• Fundamental Spacing 1.528 m

Date: April 14, 2014
Utilized:
17 GHz (17 mTHz) R+L
Central 16 elements aligned East-West

NRO 45 m

17

Experiment Setup

Yokogawa DLM4058
8 CH 1.25 GS/s, BW 500 MHz
Simultaneous sampling

8HEMT RXRF 17 GHz
TRX= 360 K
IF freq 200 MHz
BW 80 MHz
(Walsh phase switching)818

Nobeyema Radioheliograph at 17 GHz
Amplitude
Correlation

Intensity
Correlation

delay

Correlation amplitude

Ezawa, Matsuo et al. (2015)

Delay vs Time
Derive the delay for eachNeighboring antenna pairs

Transmission delay
varies for each antenna

Correct for transmission
delay and average overantennas

Data fits to the delay
calculated from Earthrotation

Delay cased byEarth rotation

Delay time accuracys < 5-10 ps20

Experiment at 17 GHzwith Nobeyama Radioheliograph⚫ Real Part of Visibility– (Intensity Correlation)0.5⚫ Imaginary Part– Δφ = 2 π ν Δt

Van Cittert
ZernikeNobeyema Radioheliograph at 17 GHz
Antenna Temperature T A* [K]Amplitude
Correlation

IntensityCorrelation

System Temperature Tsys [K]delayCorrelation amplitudeFrequency  [Hz]Bandwidth  [Hz]Tsys11t = * [s]T A  t 
 = 2t [rad]t ~ 5ps in 50 ms integration
Ezawa, Matsuo et al. (2015)

Amplitude vs. Intensity Interferometry
contribution of receiver noise and phase error
Amplitude = 10 GHz, t=60 sec
Phase error 50 mm

Intensity = 100 GHz, t=600 sec
Phase error 50 mm⚫ Betelgeuse like star with acompanion.
TA* = 0.13 K, Tsys = 500 K,
 = 1 THzusing 10-m dish with 6-km baseline
Amplitude = 10 GHz, t=60 sec
Phase error 100 mm

Intensity = 100 GHz, t=600 sec
Phase error 100 mm~2000 visibility points (uniform weight) for image reconstruction⚫ Longer integration time forintensity interferometry⚫ Intensity correlation is stableagainst large phase error.

Background limited observation withSpace Far-IR Intensity Interferometry⚫ Quantum noise of heterodyne receivers– TQL = h/k [K] = 150 K @ 3THz

10-14

– n = kTQLB/h = B [photons/s]⚫ Background limit of direct detectors

Quantum Limit– NEP = 10-19 W/Hz0.5, B =100 GHz– TRX = NEP / (2k B0.5) = 10 mK

10-16
Atmospheric Limit

10-17– Background vs. Quantum limit~ 4 orders

10-18
Cosmic Background Limit
10-19

NEP [W/√Hz](approximate value)

10-15

Intensity Interferometry⚫ Cross correlation of Intensity (E2)
– Missing phase information⚫ Stable against phase fluctuation– Coherence lengths >> Wavelengths⚫ Photon counting detector can be used
– High sensitivity, no receiver quantum limit⚫ High correlation efficiency in infrared⚫ Photon bunches enable delay measurements

Terahertz Photon Rates⚫ Atmospheric emission (100 pW )– 100 G photon/s⚫ Cosmic Microwave Background– 100 M photon/s (=300 GHz, B=100 GHz)

⚫ Cosmic Terahertz Background (10-16 W)– 100 k photon/s⚫ 1 Jy sources (=10-26 W/m2/Hz)– 100 M photon/s (B=100 GHz, f=10 m)⚫ Receiver Quantum Limit– P = hB → 100 G photon/sRequirements to Detectors⚫ Sensitive to THz photons
Matsuo and Ezawa, JLTP (2016)– Photon energy ~10-21 Joule⚫ Fast response/ = 3– B = 1 GHz for 100 M photons/s⚫ NEP(Noise Equivalent Power)= 10-21 × (1 GHz)0.5~ 10-17 W/Hz0.5

OurTargetSPICA

SIS Photon Detectors

N = 2eI 0 [A/ Hz ]Photon Assisted Tunneling
IJc =300A/cm2h/eh

2I 0NEP =
[W/ Hz ]e
NEP  3  10−18W/ Hz

for I 0 = 1 pA  = 0.5

at 650 GHz

Low leakage SIS junctions

VLeakage current [A]eS = [A/W]h

10 mm × 10 mm
5 mm × 5 mm
3 mm × 3 mm

BCS
BCS+leak2/e

Ezawa et al., JLTP (2019)

Temperature [K]Superconducting detectors in THz frequencies
An example of superconductingdetector at 10um (30THz)
Kawakami et al. (2019)

An antenna-coupled Nb-SIS photon detector
at 650 GHz fabricated in CRAVITY

Ezawa et al. (2020) JLTP

New Detector Design⚫ Low readout capacitance~ 10 fF⚫ Low loss CPW

Readout Electronics⚫ Low Gate Leakage– Less than 1 pA

⚫ Low Gate Capacitance– Less than 10 fF⚫ Low Power Dissipation– Less than 100 uW @0.8K– Less than 10 mW @4K– GaAs-JFET or Junction-pHEMT ?

Junction-pHEMT

8.E-05

8.E-04

7.E-05

7.E-04

6.E-05

6.E-04
Drain Current (A)I-Vcharacteristics

Drain Current (A)GaAs-JFET

5.E-05
4.E-05
3.E-05
2.E-05

5.E-04
4.E-04

3.E-04
2.E-04

1.E-05

1.E-040.E+00

00.5

1

1.5

2

2.5

3

0.E+0002.E-13

2.E-13

1.E-13

1.E-130.E+00GATE LEAKAGE (A)GateLeakage current

GATE LEAKAGE (A)drain voltage(V)-1.E-13-2.E-13-3.E-13-4.E-13

0.5

1
1.5
2
drain voltage(V)2.5

3

0.E+00-1.E-13-2.E-13-3.E-13-4.E-13-5.E-13-1-0.5GATE VOLTAGE(V)00.5-5.E-13-1-0.50
GATE VOLTAGE(V)

0.5Noji, Koseki and Matsuo (2020)

Readout Electronics

SIS photon detector signal
One electron/photon with abandwidth of 1 GHz.
Assuming,

Capacitance = 10 fF
𝑒𝑉𝑠 = = 16 𝜇V
𝐶

J-PHEMT

1k

J-PHEMT400

50

FET thermal noise at 0.8K

8:1

𝑣𝑛 =SiGe amplifier

100uW

0.8K

36mW

4K

4𝑘𝐵 𝑇𝑅𝐷 = 0.2 𝑛V/ 𝐻𝑍𝑑𝑉𝑔
1𝑅𝐷 === 1 kΩ𝑔𝑚 𝑑𝐼𝑑With a bandwidth of 1 GHz,

𝑉𝑛 = 𝑣𝑛 × 𝐵 = 6 𝜇Vrms

Development of 0.8K He4 sorption coolers
Operational Temperature: 0.8K
Cooling Capacity: larger than 200 uW
Compact: height less than 900 mm
Heat Load to 4K: less than 100 mW

Niwa et al. (2020) EA Receiver Workshop

A Cryostat for THz Photon Statistics

Ezawa and Matsuo

Experimental Setup for Intensity Interferometry

Input Optics

0.8K Fridge

SIS-PC

RecorderCryogenic
Electronics
4K Cooler
Rotatable Mask
Thermal Source

The Most Transparent Atmosphere from Dome A
Ice Feature at 7 THz[NII]
1.5 THz[OIII]
5.8 THz[OIII]
3.4 THz

August 9th 12-18h UTC, 2010Matsuo et al. Advances in Polar Science (2019)Antarctic THz Intensity
Interferometry

Two 30-cm THz telescopes

RecorderB > 1GHz

RecorderB > 1GHz

Calculate correlation and delay

Technologies forSpace Far-IR Interferometry• Cryogenics - AKARI, SPICA, Astro-H• VLBI technology - HALCA, Astro-G• Superconducting detectors - SMILES

Formation
FlightPhoton Counters
Atomic clock
RecorderPhoton Counters
Atomic clock
RecorderCombination of OST and MSO• Large Cryogenic Telescopes in THz• Direct detectors will be installed.
• Both will situate around S-E L2

Far-InfraredIntensity Interferometry
Credit: EHT Collaboration• Closer to the central activities !

ALMA (ESO/NAOJ/NRAO), Imanishi et al.
Inoue, Tamura, Matsuo et al. (2016)

Credit: ALMA (ESO/NAOJ/NRAO)

Credit: ALMA/NAOJ

Angular Scale of Observation
All Sky

3°10″

10 mas

10 mas91011
12
13Log Frequency [Hz]14

Problems to be solved• Time scale of the project– Ground-based demonstration• Wavelengths of interests– Is delay calibration possible in infrared ?

• Fast photon counting technologies– Superconducting detectors• Precision satellite orbit determination– Formation flights• Fast data rates

Summary• High angular resolution Far-IR observations• HBT intensity interferometry• Imaging technique• Merit of direct detectors• Combination of OST and Millimetron• Ground-based demonstrators