National Institute of Standards and Technology Broadband Spectroscopy of CO 2 Bands Near 2μm Using...

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National Institute of Standards and Technology Broadband Spectroscopy of CO 2 Bands Near 2μm Using a Femtosecond Mode-Locked Laser ISMS 2014 - Session TI.09 17 June 2014 Andrew Klose 1 , Daniel L. Maser 1 , Gabriel Ycas 1 , Ian Coddington 2 , Nathan Newbury 2 , and Scott A. Diddams 1 National Institute of Standards and Technology 1 Time and Frequency Division 2 Quantum Electronics and Photonics Division Boulder, Colorado

Transcript of National Institute of Standards and Technology Broadband Spectroscopy of CO 2 Bands Near 2μm Using...

Page 1: National Institute of Standards and Technology Broadband Spectroscopy of CO 2 Bands Near 2μm Using a Femtosecond Mode-Locked Laser ISMS 2014 - Session.

National Institute ofStandards and Technology

Broadband Spectroscopy of CO2 Bands Near 2μm Using a Femtosecond Mode-Locked Laser

ISMS 2014 - Session TI.0917 June 2014

Andrew Klose1, Daniel L. Maser1, Gabriel Ycas1, Ian Coddington2, Nathan Newbury2, and Scott A. Diddams1

National Institute of Standards and Technology1Time and Frequency Division

2Quantum Electronics and Photonics DivisionBoulder, Colorado

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Outline

• Why use optical frequency combs?

• 2 micron fiber laser source

• 2D Virtually-imaged phased array spectrometer

• Preliminary carbon dioxide measurements near 2 microns

• Future plans

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Optical Frequency Combs

• Optical frequency comb consists of many (>105) lines equally-spaced in frequency

• All lines defined by two radio frequencies:

• Spectroscopy with combs is advantageous => broadband source of many “cw” lasers

Femtosecond Optical Frequency Comb. Ye and Cundiff (Eds.). Springer, Norwell, MA (2005).

𝑓 (𝑛)= 𝑓 0+𝑛 ∙ 𝑓 𝑟𝑒𝑝

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Spectroscopy with Combs• Femtosecond mode-locked fiber lasers are a well-

developed technology => straightforward to implement

• Er:fiber laser + nonlinear optical processes =>light in IR/MIR => broadband/precision spectroscopy

• Spectroscopy measurements benefit from stable source of laser light

• Polarization maintaining optical fibers => increased robustness of optical source

For previous work, see, for example: G. Ycas, et al. Opt. Lett. 37, 2199 (2012) S. Kumkar, et al. Opt. Lett. 37, 554 (2012) I. Hartl, et al. CLEO Technical Digest. CTh1J.2 (2012) A. Sell, et al. Opt. Exp. 17 1070 (2009) H. Hoogland, et al. Opt. Exp. 21, 31390 (2013)

• 2µm spectral region interesting for CO2 spectroscopy

• 2µm => supercontinuum generation from Er:fiber

L. S. Rothman, et al. J Quant. Spec. Rad. Trans. 130, 4 (2013)

Blue – H20Red – CO2

250 MHz Er:fiber Laser

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Source Setup• 25mW of from 250 Er:fiber oscillator (non-PM)

• EDFA Amplifier => 350 mW average output power, 70 fs pulses

• EDFA output launched into highly nonlinear fiber (HNLF) (small mode field diameter=>nonlinear effects)

• 240 mW of average power spanning an optical octave after HNLF

Connectorized Output

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Output from Source

3

• Output spectrum spans 1.1 μm - 2.2μm

• The spectral peak near 2μm can be tuned by altering the optical power incident the HNLF

• Altered average EDFA output power by varying 980 nm pumping current

• Relatively flat individual spectra spanning 50-100 nm

• 90 fs pulses in 2μm region at connectorized output (can compress to 35 fs)

Total power = 240mW

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Stability of Source• Recorded 250 optical spectra at intervals of 15 minutes over 2.5 days

• Free Running setup - no stabilization of Er:fiber oscillator

• Analyzed variation of spectrum• For each resolution element from the optical spectrum analyzer• Integrated intensity variation of 2μm region

• Overall intensity drift of 2μm spectral region is a few percent over a timescale of days

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VIPA Spectrometer

Fiber-CoupledLight

Cylindrical Lens

Grating

Spherical Lens

InSb 2D-camera

• Comb teeth are spatially dispersed in 2D

• Virtually Imaged Phased Array (VIPA) => vertical dispersion

• Orth. Diffraction Grating =>horizontal dispersion

• Simultaneous measurement of ~50nm bandwidth of spectrum

• Typical resolution 0.5 – 2 GHz

[1] M. Shirasaki. Opt. Lett. 21, 366 (1996)[2] S. Diddams, et al. Nature. 293, 627 (2007)[3] L. Nugent-Glandorf, et al. Opt. Lett. 37, 3285 (2012)

[1]

[2]

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Calibration of 2D Image

250 MHzSource

• Resolution of VIPA is ~1GHz

• Filter 250 MHz source lines to 5 GHz

• Use 5 GHz filtered comb to calibrate camera pixels to laser frequency

• VIPA FSR ~50GHz => count dots, fit dots, generate x,y pixel to frequency map

• Use unfiltered source for spectroscopy measurement

Spectrometerand Camera

5 GHzFabry Perot

Cavity

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Obtaining Spectrum

• Background image

• Sample image

• Dark image

• Subtract dark image from background and sample

• Spectrometer is fiber coupled=> No alignment change between calibration, background, or sample

=Frequency →

Light passed through ~12 cm cell at 700 mbar with ~200 mbar CO2

re-coupled into fiber and sent to spectrometer

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Example Spectra

[1] L. S. Rothman, et al. J Quant. Spec. Rad. Trans. 130, 4 (2013)

12 cm path200 mbar CO2

[1]

Two GratingPositions

• Resolution of <2 GHz achieved (~0.05cm-1)

• Simultaneous measurement of 40 nm bandwidth(~2000 spectral elements)

• < 1ms integration time

• Fluctuations at <1% level => time dependent etalon• Detailed analysis currently underway

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Future Plans• Continued Spectroscopy

with VIPA-based system

• Multiheterodyne dual comb spectroscopy [1,2]

• Open air atmospheric measurements on 2km path on NIST-Boulder Campus [3]

• Implement source with PM oscillator [3]

[1] F. Keilmann, et al. Opt. Lett. 29, 1542 (2004)[2] A. Schliesser, et al. Opt. Exp. 13, 9029 (2005)[3] G. Rieker, et al. arXiv:1406.3326v1 [physics.optics][3] L.C. Sinclair, et al. Opt. Exp. 22, 6996 (2014)

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Summary• 2 micron source was constructed => based on supercontinuum generation from

Er:fiber oscillator• <100fs pulses• ~30mW power in relevant bandwidth region• Flat, tunable spectrum• Robust comb source

• Spectroscopy of carbon diode using 2D VIPA-based Spectrometer• Resolution on the order of 1 GHz• 40 nm simultaneous bandwidth measured• <1ms integration time

• Continued work on• VIPA spectroscopy• Dual Comb Spectroscopy• Open-air measurements• Portable source

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AcknowledgementsThank You!

NISTScott DiddamsGabe YcasDan MaserDan HackettNate NewburyIan CoddingtonEsther BaumannFabrizio GiorgettaLaura SinclairLindsey SonderhouseBill Swann

CU-Boulder/JILAJun Ye

CU-BoulderGreg Rieker

U of CampinasFlavio Cruz

St. JohnsTodd Johnson

Funding:NRCNIST Climate Science

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Source Coherence and Noise

frep 2frep

Heterodyne beats

• 2µm portion of spectrum was frequency doubled in PPLN crystal

• Free-running heterodyne beat note with 980nm external cavity diode laser measured

• 25 dB S/N beat note was recorded with 100 kHz resolution bandwidth

2000nm LPF

1850nm LPF

Red = 1650nm LPFGreen = Full SupercontinuumBlack = Er:fiber Oscillator

• Relative intensity noise (RIN) from supercontinuum increases with decreasing spectral window

Green – Full SCRed – 1650nm LPFBlue – 1850nm LPFPurple – 2000nm LPF

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Pulse Width

SHG-FROG

ConnectorizedLaser Output

• Output of source was temporally compressed using silicon prisms

• Pulses were analyzed via SHG-Frequency Resolved Optical Gating (SHG-FROG)

• Achieved FWHM pulse width of 35 fs• Transform limit of 20 fs• SHG-FROG-retrieved optical spectrum in good

agreement with direct spectrum measurement