Tunable CW THz Source

Principles of Operation andApplication Data

Gregor KupkaJoachim Sacher

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Outline

CW THz Generation via Frequency Mixing of Tunable Diode Lasers Motivation

Selected Application Examples

Instrument Layout Principles of CW THz Generation Coherent CW THz Detection Method

Technical Data THz Generation

Frequency Mixers

Laser Sources Frequency Tuning Fast Frequency Scanning Frequency Stability

Laser Controller Electrical Noise Characterization Optical Noise Characterization Relative Intensity Noise

Software

Application Examples

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Motivation

Selected Application Examples Airport Screening for weapons

explosives, drugs or other contrabands

Secure wireless communication Cancer detection, wound

inspection and other medical imaging

Biochip analysis of DNA, proteins, and other biological materials

Biological warfare agents Detection of land mines and

buried explosive devices Monitoring manufacturing

processes Measuring water content of food

to detect spoilage Inspection finished production

through packaging

Determining the thickness of a layer of paint while it is still wet

Quality control of insulated wires during manufacture

Inspecting semiconductors wavers for defects

Inspecting (and reading) of unopend mail

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Principles of CW Tera Hertz Generation

Generation of Tunable CW Tera Hertz Radiation There are no room temperature operational CW THz radiation sources

Quantum cascade based developments still require a decade of development

Technical realization of CW THz radiation Difference frequency generation of two CW lasers

Schematic Layout of a CW Tera Hertz measurement setup

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Principles of CW Tera Hertz Generation

Higher Power Options for future THz Frequency Mixers Solutions with optical amplifiers

More than 300mW power for beat frequency generation available

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Coherent CW Tera Hertz Detection Method

Setting the THz Frequency via the Wavelength of the Pump Lasers The THz Frequency setting is performed via the temperature of the DFB

Lasers The THz Frequency may be verified via a Spectrometer

Changing the Phase between THz Sender and the THz Receiver The Phase is changed via the fiber-optical Delay line. Alternatively, a Phase change can be performed by the current of the DFB

Lasers

Phase Changes causes Interference Pattern within the Receiver The THz radiation of the Sender and the Receiver interfere within the

Receiver unit Absorption of THz Radiation within the Sample can be detected via the

Change of the Amplitude of the Interference Pattern

Lock-In Detection of the THz The Lock-In Detections allows the Measurement of the THz Absorption Improved Signal to Noise Ratio

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CW Tera Hertz Generation

CW THz Frequency Mixers Technology Requirements

Low carrier lifetime for high frequency THz radiation generation High carrier mobility for high intensity THz radiation generation

Fiber Coupled Design High coupling efficiency No alignment issues Easy to use

THz Beam Performance Precollimated THz beam

via Silicon Lens

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CW Tera Hertz Generation

Performance Data

Frequency Dependence:100GHz 1.5µW (spec.)500GHz 0.5µW (spec.)

1000GHz 0.1µW (spec.)1500GHz 0.05µW (spec.)

760 770 780 790 800

-50

-40

-30

-20

-10

0

Sidemode supression 39 dB

Sig

nal [

dBm

]

Wavelength [nm]

without Master Laser

with Master Laser

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Laser Souces for CW Tera Hertz Generation

Fiber Coupled Laser Solution for CW Tera Hertz Generation

Laser System Tuning Performance

DFB Wavelength Tuning

851,5

852,0

852,5

853,0

853,5

854,0

854,5

855,0

855,5

15 20 25 30 35 40 45 50

Temperature / °C

Wav

elen

gth

/ nm

Wavelength DFB 1

Wavelength DFB 2

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Laser Souces for CW Tera Hertz Generation

Fast THz Frequency Scanning Capability via DFB Temperature Scanning

0 20 40 6018

20

22

24

26

28

30

32

779,800

779,900

780,000

780,100

780,200

780,300

780,400

780,500

Periodic Temperatur Scan Setpoint Dither 20°C

Tem

pera

ture

/ °C

Time /sec

10sec periodic temperature scan

Wav

elen

gth

/nm

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Laser Souces for CW Tera Hertz Generation

Long Term Stability without external stabilization

Video

http://data.sacher-laser.com/video/mov01178-smaller.wmvhttp://data.sacher-laser.com/video/mov01178.mpg

Free Running Stability better than 50MHz

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Laser Controller for CW THz Generation

Experimental Setup

Sub 500nA Noise Figure

Reference Modulation

10 ResistorΩ

DC Current

Electrical Spectrum AnalyzerLaser Controller Bias-Tee

0,0 20,0k 40,0k 60,0k 80,0k 100,0k0,0

12,8

25,6

38,4

51,2

64,0

76,8

89,6

102,4PilotOEM 500, Battery operated

ES

A A

mpl

itude

/ dB

m

Frequency / Hz

500nA RMS

0,0 200,0k 400,0k 600,0k 800,0k 1,0M0,0

12,8

25,6

38,4

51,2

64,0

76,8

89,6

102,4 Pilot OEM 500, Battery operated

ES

A A

mpl

itude

/ d

Bm

Frequency / Hz

500nA RMS

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Laser Controller for CW THz Generation

Experimental Setup

Sub 700nA Noise Figure

Reference Modulation

Laser Diode

DC Current

Photo Diode

Laser Controller Bias-Tee

Electrical Spectrum Analyzer

-20k 0 20k 40k 60k 80k 100k 120k 140k 160k 180k-100-95-90-85-80-75-70-65-60-55-50-45-40-35-30-25-20-15-10

-50

7µA RMS Noise Level

Noi

se V

olta

ge /d

B

Frequency/ Hz

Optical Noise Measurement PilotOEM 500

0.7µA RMS Noise Level

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Laser Controller for CW THz Generation

Relative Intensity Noise Experimental Results in Cooperation with TU Darmstadt

Excellent Noise Figure of Sacher Laser Controller Noise Figure determines the Linewidth of DFB Lasers Controller defines Stability of THz Frequency

0 200 400 600 800 1000 1200 1400

-80

-75

-70

-65

-60

-55

-50

Other Manufacturer 24V Batterie Pilot OEM

Cur

rent

Noi

se (

dBm

)

Injection Current (mA)

0 10 20 30 40 50 60 70 80 90 100 110 120-170

-160

-150

-140

-130

-120

-110

RIN

(dB

/Hz)

Injection Current (mA)

24V Batterie Pilot OEM Other Manufacturer

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CW THz System Software

Complete Measurement Software

Programmed in LabView

Auto-Calibration of System Data

Calibration Data stored in Status File

Fully Automated Measurement Algorithmn Frequency Scan of Samples Phase Scan of Samples 2D Position Scanning of Samples

Flexible Storage of MeasurmentResults on Hard Drive

Programmstart

EingabemaskeProbe, Scanbereich

Eingabemaske Lasersystem

Auslesen / Ändern

Eingabemaske Lock-In VerstärkerAuslesen / Ändern

Probe X-Positionanfahren

Probe Y-Positionanfahren

THz Frequenzanfahren

PhasenscanStartposition

anfahren

Lock-In Verstärkerauslesen

Daten abspeichern

PhasenscanEndposition erreicht ?

THz ScanEndposition erreicht ?

Y-PositionEndpositionerreicht ?

X-PositionEndpositionerreicht ?

Programmende

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CW THz System Software

Selftest Procedure

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CW THz System Software

Frequency Calibration

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CW THz System Software

THz Tuning AlgorithmnTHz Tuning Algorithmn

15

20

25

30

35

40

45

50

0 5 10 15 20 25 30 35

Tuning Parameter

Lase

r Tem

pera

ture

/ °C

Temperature DFB 1

Temperature DFB 2

DFB Tuning

851,5

852,0

852,5

853,0

853,5

854,0

854,5

855,0

855,5

856,0

0 5 10 15 20 25 30 35

Tuning Parameter

Wav

elen

gth

/ nm

Wavelength DFB 1

Wavelength DFB 2

Frequency Tuning

350,4

350,6

350,8

351,0

351,2

351,4

351,6

351,8

352,0

352,2

352,4

0 5 10 15 20 25 30 35

Tuning Parameter

Fre

que

ncy

/ T

Hz

Frequency DFB 1

Frequency DFB 2

Frequency Tuning

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

0 5 10 15 20 25 30 35

Tuning Parameter

TH

z F

req

uen

cy /

TH

z

THz Frequency

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CW THz System Software

THz Frequency Tuning

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CW THz System Software

THz Phase Tuning

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Optional Schemes for Improved Stability

Frequency Stability with Temperature Stabilized DFB Lasers Temperature stabilized DFB lasers achieve a frequency stability of better than

50MHz Application which require a better frequency stability require an active frequency

stabilization

Active Frequency Stabilization of DFB Lasers DFB Lasers can be locked either to an atomic reference as Rubdium, Caesium or

other atomic references DFB Lasers can be locked to a technical reference as an etalon cell or a Fabry Perot

Interferometer

Locking Schemes Sacher Lasertechnik offers various locking schemes for tunable diode lasers. Several schemes as used for Side of Fringe and Top of Line type of lock

Advantages of Frequency Locking for THz Generation Minimization of Frequency drift Minimization of Phase noise Work presented at THz Workshop Kaiserslautern 2008

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Optical Tera Hertz Setup

THz Setup

CAD Layout

Realization

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Optional Schemes for Improved Stability

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Selected Application Examples

Impurity of a Chocolate Bar

in Cooperation with TU Braunschweig, Martin Koch

10 20 30 40 50 60

10

20

30

40

50

60

X position [mm]

Y p

ositi

on [m

m]

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Selected Application Examples

Mirror Reflectivity: 13 layers of alumina (A) + 12 layers of alumina-zirconia ( AZ) sintered together to a solid ceramic block

in Cooperation with TU Braunschweig, Martin Koch

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Award Winning Product

PhAST/Laser Focus World 2006

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Thank You For Your Attention!

Sacher Lasertechnik GmbHRudolf-Breitscheid-Str. 1-535037 MarburgGermany

Sacher Lasertechnik LLC .5765 Equador WayBuena Park, CA 90620United States

http://www.sacher-laser.com© 2009 Sacher Lasertechnik GmbH. All rights reserved.