Spectroscopic detection using a tunable frequency comb
AssigneePilot Photonics Ltd.
InventorsJules BRADDELL, Frank SMYTH
Life of this patent
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Abstract
A method of performing spectroscopic measurements provides an optical frequency comb, and directs the comb through or at a sample. The optical frequency comb is generated by gain switching a laser diode constructed from Gallium Nitride and related materials. Various techniques are described for manipulating the comb source to achieve desired benefits for spectroscopy.
Claims43
A method of performing spectroscopic measurements, the method comprising the steps of providing an optical frequency comb, and directing the comb through or at a sample.
A method as claimed in any preceding claim, wherein the gain switched laser diode, is constructed with quantum wells made from InGaAs, strained or otherwise in the active region, and the spectroscopic detection is in near infra-red and infra-red region of the electromagnetic spectrum.
A method as claimed in any preceding claim, wherein the gain switched laser diode is constructed with Gallium Indium Arsenide Antimonide (GaInAsSb) or related materials, and the spectroscopic detection is in infra-red region of the electromagnetic spectrum.
A method as claimed in any preceding claim, wherein the gain switched laser diode is constructed as a quantum cascade laser, and the spectroscopic detection is in infra-red and far infra-region of the electromagnetic spectrum.
A method as claimed in any preceding claim, wherein the apparatus carries out direct absorption spectral measurements that are dispersed by a diffractive element such as a grating.
A method as claimed in any preceding claim, wherein the comb lines are passed through a sample and are then spatially fanned out in wavelength or frequency before being monitored by a CCD array or separated by a device such as an optical spectrum analyser or Fourier transform spectrometer.
A method as claimed in any preceding claim, wherein the emission comb is set to approximately the same as the absorption comb or a multiple of the absorption comb so that the emission comb is in gaps between the absorption bands, and the incident comb will experience little or no absorption.
A method as claimed in any preceding claim, wherein the optical frequency comb is used to modify the FSR to match, or a whole multiple thereof to match, the frequency separation of two or more molecular absorption bands at the centre wavelength of the comb, and/or to modify the FSR so that some or all of the comb lines interact with the absorption bands of the molecule, whereby a comparison of the transmissions can then be made to determine the concentration and presence of a molecular species.
A method as claimed in any preceding claim, comprising the steps of using the filter characteristic of a resonant cavity to increase the resolution of a spectrophotometer by using a comb source with an FSR a fixed multiple (N) of the FSR of the resonant cavity and then using the resonant cavity to selectively pick off every N comb lines and present this to a spectrometer, moving to N+1 in the resonant cavity and then presenting sequentially to a spectrometer, then N+2 and so on until an entire spectrum is built up.
A method as claimed in any preceding claim, wherein a time resolved transmission or reflection spectrum is resolved and the ultimate resolution of a spectrophotometer is improved by a factor of N limited by the resolution of the comb line.
A method as claimed in any preceding claim, wherein the optical frequency uses a high finesse optical cavity that acts as a storage device for optical radiation, and monitoring of the decay of those comb lines is performed after the source is switched off to determine the optical absorption within the cavity.
A method as claimed in any preceding claim, wherein the apparatus uses two optical frequency combs and mixes these combs on a detector to create a RF beat frequency and the interrogation of the RF spectrum to determine the absorption or transmission of comb lines.
A method as claimed in any preceding claim, wherein the apparatus uses the optical frequency comb for coherent anti-Stokes Raman spectroscopy.
A method as claimed in any preceding claim, wherein the apparatus uses the optical frequency comb to probe emitted spectral lines from a Plasma or other source by using an RF beat frequency.
A method as claimed in any preceding claim, wherein the apparatus uses the optical frequency comb to probe emitted spectral lines from an astronomical source to examine red-shifts.
An apparatus for performing spectroscopic measurements, the apparatus comprising an optical frequency comb source, means for directing the comb through or at a sample, a detector for monitoring radiation from the sample, and a controller for performing a method as claimed in any preceding claim.
Dependencies are inferred from the claim text.