A New E-Band (60 – 90 GHz) Fourier Transform Millimeter-wave Spectrometer

DeWayne T. Halfen and Lucy M. Ziurys

Department of ChemistryDepartment of Astronomy

Steward ObservatoryArizona Radio Observatory

University of Arizona

June 19, 2013

Arizona

ObservatoryRadio

Why E-band ?Why E-band ?

• U-band (40 – 60 GHz) upgrade very successful• Takes the output of our existing 4 – 40 GHz system and

multiplies (x2) up into 40 – 60 GHz• Uses U-band (WR-19) waveguide components for radiation

generation and detection and a smaller mirror• Keep pushing the envelope of cavity-FTMW instrumentation

• Some molecules need measurements of higher transitions than covered in our current range– e.g. ScO (WH08)

• Designed a higher frequency band from 60 – 90 GHz, using WR-12 waveguide components with the same mirror

Original Fourier Transform Microwave Spectrometer

• Operated from 4 – 40 GHz

• 20 in. Al mirrors• Quarter-wave antennas• Pulsed valve at 40o to

Fabry-Perot cavity • 22 in. cryopump• Nd/YAG laser

Top View

E

A

B

C

Dn 0+

d

LNA30 dB

PIN Switch

+ d

0-50 dB

TTL Pulse Sequence

High Voltage

Solenoid Valve

4-40 GHz

n0n0Mixer

Computer

Coupler

Pulse Driver

S1

S3

S4

S4

S2

A/D

S3

LP

F

+ –

Laser Beam

Internal window

20 in. mirrorsQuarter-wave antennas

Block Diagram of New E-Band System

n0 +

d

PIN Switch

+d

18.75-37.5 GHz

n0 n0 ComputerCoupler

Mixer

Multiplier/ Amplifier

LNA

x2/x4

Amplifier

LPF

x2/x4

Amplifier

Multiplier/ Amplifier

Coupler

RF Detector

A/D

60-75 GHz75-90 GHz

E-Band System

• Diamond-cut Al mirrors with inner Brass plug– 170 mm (6.7 in.) diameter with 838 mm (33 in.) radius of curvature– Incorporated into existing vacuum chamber and spectrometer setup

• Replaced WR-19 devices with WR-12 components• Use a JPL/NRAO MMIC Low Noise Amplifier (LNA) (E. Bryerton)

Radiation Source

ActiveDoubler orQuadrupler

Isolator

WaveguideCoupler

Cu MountingPlate

WR-19 to WR-12Transition

Detection Electronics

ActiveDoubler orQuadrupler

Isolator LNA

CouplerMixer RF Detector

WaveguideCoupler

Cu MountingPlate

WR-19 to WR-12Transition

Isolator

Detection Electronics

ActiveDoubler orQuadrupler Isolator LNA

CouplerMixer RF Detector

WaveguideCoupler

Cu MountingPlate

WR-19 to WR-12Transition

Isolator

Cavity Mode Structure

• Only prominent cavity modes – q modes spaced every half wavelength apart– ~2 mm in mirror distance or 80-100 MHz in frequency space– Overtone q modes more prominent in E-band than U-band

• Q factor around 100,000 from 60 – 90 GHz– Q for 40 – 60 GHz – 80,000 – 100,000

• Tested system on OCS and its isotopologues (0.5 % OCS in Ar)

First Light Spectra

Frequency (MHz)60618.4 60618.6 60618.8

0

5

10

15

O13CS (X1+): J = 5 4In

ten

sity

(m

V)

100 shots

Frequency (MHz)71192.8 71193.0 71193.2

0

5

10

15

20

OC34S (X1+): J = 6 5In

ten

sity

(m

V)

100 shots

Frequency (MHz)72057.4 72057.6 72057.8

0.0

0.2

0.4

0.6

OC33S (X1+): J = 6 5In

ten

sity

(m

V)

500 shots

Frequency (MHz)70939.6 70939.8 70940.0

0.00

0.05

0.10

0.15

0.20

O13C34S (X1+): J = 6 5In

ten

sity

(m

V)

2000 shots

• Used Discharge-Assisted Laser Ablation Source (DALAS)

• Steel ablation adapter with Teflon discharge nozzle

• Metal vapor mixed with dilute reactant gas in Ar

• DC discharge

Gas Phase Synthesis

MotorHousing

MetalRod

DischargeNozzle

PulsedValve

AblationAdapter

Docking Station

MetalRod

• Also recorded spectra for AlO, VO, NiC, and ScC2

Free Radical Spectra

Al vapor + 0.1 % N2O in Ar, no DC

V vapor + 0.1 % N2O in Ar, no DC

Frequency (MHz)76579.4 76579.6 76579.8

0.0

0.2

0.4

0.6

0.8

1.0

1.2

AlO (X2): N = 2 1In

ten

sity

(m

V)

3000 shots

J = 2.5 1.5, F = 5 4

Frequency (MHz)69726.6 69726.8 69727.0

0.0

0.1

0.2

0.3

0.4

0.5

VO (X4 ): N = 2 1In

ten

sity

(m

V)

1000 shots

J = 3.5 2.5, F = 7 6

Frequency (MHz)76463.4 76463.6 76463.8

0.00

0.05

0.10

0.15

0.20

0.25

0.30

58NiC (X1): N = 2 1In

ten

sity

(m

V)

4000 shots

Frequency (MHz)76027.6 76027.8 76028.0

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

60NiC (X1): N = 2 1In

ten

sity

(m

V)

5000 shots

Ni vapor + 0.5 % CH4 in Ar, 600 V DC

5000-10000 shots

Frequency (MHz)

62497.8 62507.1

F = 6 5

J = 3.5 2.5

62550.7 62561.862545.1 62546.5

F = 7 6

F = 5 4

J = 4.5 3.5

ScC2 (X2A1): NKa,Kc

= 404 303

F = 6 5F = 7 6

F = 8 7

Sc vapor + 0.5 % CH4 in Ar, 1000 V DC

• 60 – 90 GHz FTmmW system successfully constructed using waveguide devices

• Mode structure very clean• Spectra with high S/N ratio obtained

• More data from this system presented next– ScO – WH09

• Build separate spectrometer to utilize U and E-band systems

Conclusions and Future DirectionsConclusions and Future Directions

AcknowledgementsAcknowledgements

• Lucy Ziurys• Aldo Apponi• Bob Freund• Jessica Edwards• Jie Min• Gilles Adande• Matt Bucchino• Julie Anderson• Debbie Schmidt

• NSF• NASA