Applications of Cavity-Enhanced Direct Frequency Comb

Spectroscopy

Kevin Cossel

Ye Group

JILA/University of Colorado-Boulder

OSU Symposium on Molecular Spectroscopy 2010

What is CE-DFCS?

The 3 building blocks of Cavity-Enhanced Direct Frequency Comb Spectroscopy:

1 Mode-locked laser (frequency comb)

2 High-finesse enhancement cavity

3 Dispersive detection system

M. J. Thorpe and J. Ye, Appl. Phys B 91, 397 (2008)

Benefits of frequency combs

from S. T. Cundiff, J. Ye, and J. L. Hall, Scientific American, Apr 2008

Single ultrashort pulse Train of pulses

Frequency combs provide narrow lines over a wide spectral bandwidth:

• High resolution• Broad bandwidth• Rapid acquisition• Spatially coherent

Multi-species detection with high sensitivity in near real time

Cavity-comb coupling

Frequency Domain

Frequency comb

Cavity modes

Time Domain

Jones & Ye, Opt. Lett. 27, 1848 (2002).

Mode-locked laser

inT

dd

cL

cFSR

2

Cavity mode structure:Frequency comb structure:

orn fnf

Thorpe et al., Opt. Express. 13, 882 (2005).

Adler et al., Annu. Rev. Anal. Chem. 3, 175 (2010).

I. Trace contaminant detection

Trace gas detection in arsineExperimental setup:• 250-MHz-Er:fiber laser with highly nonlinear fiber (≈1.2-2.0 µm)• cavity with peak Finesse of 45000 spanning 1.78-1.95 µm• arsine extremely toxic set up in specialty lab at NIST (Optoelectronics Division, K. Bertness)

45000F

Mirror data

Laser spectrum

VIPA FSR

2D Spectrometer

Mode-locked laser VIPA spectrometer

High finesse optical cavitywith intra-cavity gas sample

>3000 channels simultaneously (typically 25 nm bandwidth)~1 GHz resolution

S. A. Diddams et al., Nature 445, 627 (2007)M. J. Thorpe et al., Opt. Express 16, 2387 (2008)

Arsine Results ICoverage from 1.74-1.97 µm (5050-5750 cm-1)

Absorption sensitivity of 110-7 cm-1 Hz-1/2 in nitrogen over 3000 simultaneous channels

Measurement of H2O, CH4, CO2, H2S in nitrogen with minimum detectable concentrations from 7 ppb to 700 ppb

Arsine Results II

Detection level for water in arsine of 31 ppbK.C. Cossel et al., Appl Phys B, in press (2010).

II. Breath Analysis

Application: breath analysisMedical research has (maybe) identified many molecules as markers for certain diseases in breath.

Our focus: lung cancer & COPD

Collaborators:

CU Medical School (O. Reiss, J. Repine)

CU Cancer Center (N. Peled)

Samples: from cell cultures, rats, and humans

What are the challenges?

• many molecules present in breath samples

• complex molecules have “messy” spectra

• recognize molecule spectra

• bottom line: Can we definitely link certain molecules to cancer?

Application: breath analysis

Develop CE-DFCS system in the mid-IR

Why use comb spectroscopy?

• simultaneous detection of multiple molecule species

(generate marker pattern!)

• high sensitivity (fundamental mid-IR band!)

• fast acquisition (compared to GC-MS)

• high resolution (separate mixtures)

First test with NIR comb: M. J. Thorpe et al., Opt. Express 16, 2387 (2008)

III. Atmospheric Chemistry

Important atmospheric measurements

• Isotope ratios (13C, 18O)

• Greenhouse gases (CH4, CO2, N2O)

• Pollutants (formaldehyde, benzene, acetone, NOx, nitric acid, etc.)

• Primary organics (e.g., isoprene) lead to aerosol formation

• Need fast acquisition over a broad bandwidth with high resolution in the mid-IR

Mid-infrared OPOPower and efficiency Spectral tunability

• Fan-out PPLN crystal; 10 W Yb:fiber pump• more than 1 W over 1 µm tuning range• continuous tunability from 2.8 to 4.8 µm (0.3 µm bandwidth)

Fourier Transform Spectrometer• 22 bit, 1 MS/s digitization

• 160 MHz resolution

• 10 s sweep time

• Broad spectral acquisition

Frequency Comb• Enhancement cavity or multipass cell

• High spectral brightness = short averaging time

Mid-IR Results IAtmospheric Atmospheric/Breath

Breath Atmospheric/Breath

Mid-IR Results IIAtmospheric Atmospheric

•Multiline detection advantage•~30 scan time•3.8×10-8 cm-1 Hz-1/2 per 45,000 spectral elements•Detection limits: H2CO (40 ppb), CH4 (5 ppb), Isoprene (7 ppb), CO2 (< 1 ppb), CH3OH (350 ppb single line or 40 ppb), …

Complex Mixture Analysis

Summary• CE-DFCS provides a unique combination

of broad bandwidth, high resolution, high sensitivity and rapid data acquisition

• Detection of many species and complex mixtures in near real time

Collaborations:Scott Diddams (NIST)Martin Fermann (IMRA)Ingmar Hartl (IMRA)Axel Ruehl (IMRA)Ronald Holzwarth (Menlo)Kris Bertness (NIST - Arsine)Jun Feng (Matheson - Arsine)Mark Raynor (Matheson -Arsine)Miao Zhu (Agilent)

CE-DFCS:Mike ThorpeFlorian AdlerPiotr MaslowskiAleksandra FoltynowiczTravis BrilesKevin MollDavid Balslev-ClausenMatt Kirchner

Funding: NSF, AFOSR, NIST, DARPA, DTRA, Agilent