High Power, Low LinewidthRidge Waveguide Laser

Stabilized by Volume HolographicGrating External Cavity at 780nm

Simon RauchJoachim Sacher

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Motivation

� Focus:� Highly stable external-cavity diode lasers (ECDL) with an output power of

several hundred milliwatt

� Applications:� Optical cooling & trapping, Raman spectroscopy, LIDAR, time standards

� Means:� Feedback by volume holographic grating (VHG), compact packaging

� Advantages:� High mechanical stability, low manufacturing costs

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Laser Realization

� Laser Diode� Chip Length: 3900µm� Front Facet: AR Coated� Read Facet: HR Coated� Collimation: Separate

Collimation for Fast and Slow Axis

� Bragg Grating� Center Wavelength: 780nm� Spectral Width: 0.1nm� Reflectivity: 12%

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General Performance

� Output Power� Max. Output Power: 380 mW� Slope Efficiency: 0.8 W/A

� Side Mode Suppression� > 50dB

� Wavelength Tuning� 5.2 GHz Mode-Hop Free� Via Current: 0.5 pm/A� Via Temperature: 10 pm/K

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Wavelength Tuning

� Tuning Mechanism� (a) Initial Status� (b) Laser Current Change

� Mode position change

� (b) Wavelength Tuning� Mode position changes

relative to Grating

� (c) Defined Mode-Hop� As soon as one mode

leaves the reflectionband of the Grating, an other mode shifts in

200 220 240 260 280 300780,016

780,018

780,020

780,022

780,024

780,026

780,028

780,030

780,032

780,034

780,036

Wav

elen

gth

/ nm

Injection Current / mA

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Spectral Linewidth

� Heterodyne Measurement� Beat Node of two identical

VBG Lasers

� No External Locking applied

� Lorenzian Fit (FWHM): � 36kHz @ 1ms/2MHz

� Linewidth: 18kHz (FWHM)

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Relative Intensity Noise (RIN)

� RIN Measurement� Low, nearly constant RIN of

-136 dB/Hz above 1 kHz

� No Microphonic CavityResonances

� RIN is reduced for higherOperation Current Values

Laser Driver

Diode Laser

Detector

Oszi

Amplifier

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Application Example: Rubidium Spectroscopy

� Spectroscopy Setup� Saturated Rb Spectroscopy

� Results� Rubidium D2 Tansition� Hyperfine Lamb Dips

clearly visible� 5.4GHz stable Mode-hop

Free tuning

� Spectrum Repeats at different Power levels

200 220 240 260 280 300780,016

780,018

780,020

780,022

780,024

780,026

780,028

780,030

780,032

780,034

780,036

Wav

elen

gth

/ nm

Injection Current / mA

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Examples for Other NIR Wavelength

� 760nm: Oxigen

� 795nm: Rubidium D1

� 852nm: Cesium D2

120 180 240760,08

760,10

760,12

760,14

Wav

elen

gth

(nm

)

Current (mA)

22°C

60 80 100 120 140 160 180

794,965

794,970

794,975

794,980

794,985

794,990

794,995

Wav

elen

gth

(Vac

uum

) / n

m

Injection Current / mA

8°C

60 80 100 120 140 160 180 200

852.10

852.12

852.14

Wav

elen

gth

(Air)

/ nm

Injection Current / mA

11,2°C, mit Kappe + Fenster

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Examples for Other NIR Wavelength

� 895nm Cesium D1

� 785nm: Raman Spectroscopy

� 830nm: Raman Spectroscopy

90 100 110 120 130 140 150 160894,56

894,57

894,58

894,59

894,60

894,61

Wav

elen

gth

(Vac

uum

) / n

m

Injection Current / mA

16°C

30 40 50 60 70 80 90 100 110 120785,105

785,110

785,115

785,120

785,125

785,130

785,135

785,140

785,145

Wav

elen

gth

(nm

)

Injection Current (mA)

50 100 150

829,86

829,88

829,90

Wav

elen

gth

/ nm

Injection Current / mA

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Application Example: Raman Spectroscopy

� Spectroscopy Setup� Raman Spectroscopy 785nm

� Results� Acetone� Ethanol

0 200 400 600 800 1000 1200 1400 1600 1800 2000

100

150

200

0 200 400 600 800 1000 1200 1400 1600 1800 2000

100

150

200

250

measure time: 6saverage: 4

Ram

an S

igna

l [a.

u.]

Raman Shift [cm-1]

Ethanol

430

880

10901055 1460

1280

Acetone

790

14401727measure time: 6s

average: 4

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Summary

� A Compact, Narrow Linewidth Volume Holographic Grating Externalwith High Output Power of 380 mW at 780nm was presented

� Excellent Laser Stability and Wavelength Tunability via Laser Currentand Laser Temperature was demonstrated

� Volume Holographic Grating Period can be choosen for anyWavelength within the Visible and Near Infrared Spectral Regime

� Project is Supported by Bundesministerium für Bildung und Forschung (BMBF) within Grant 13N13402 since May 1, 2015.

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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© 2001-2015 Sacher Lasertechnik GmbH. All rights reserved.

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