Cavity enhanced absorption spectroscopy using a piecewise tunable laser and hierarchical wavelength determination

Patent metadata

Field	Value
Publication number	US-12270706-B2
Application number	US-202117402571-A
Country	US
Kind code	B2
Filing date	Aug 15, 2021
Priority date	Dec 13, 2019
Publication date	Apr 8, 2025
Grant date	Apr 8, 2025

Abstract

Improved cavity enhanced absorption spectroscopy is provided using a piecewise tunable laser by using a lookup table for laser tuning that is configured specifically for this application. In preferred embodiments this is done in combination with a laser control strategy that provides precise wavelength determination using cavity modes of the instrument as a reference.

First claim

The invention claimed is:

1. Apparatus for performing cavity ring down spectroscopy, the apparatus comprising:
an optical source having a tunable emission wavelength, wherein the optical source has two or more tuning inputs, and wherein tuning of the optical source is piecewise continuous with respect to variation of any one of its tuning inputs;
an optical cavity having two or more mirrors and configured to accept an optical input from the optical source, wherein the optical cavity is also configured to accept a sample gas such that light circulating in the optical cavity passes through the sample gas;
a ringdown controller configured to monitor the light circulating in the optical cavity and configured to couple and interrupt coupling of light between the optical source and the optical cavity;
a tuning controller configured to tune the optical source in a setpoint mode and in a control mode;
wherein the control mode is closed-loop control of a single control input of the optical source to tune output wavelength of the optical source;
wherein the setpoint mode is an open-loop tuning of the optical source using all tuning inputs according to a lookup table configured to maximize a nonzero mode-hop free wavelength range around each output wavelength when using the control mode;
wherein the optical source is a sampled grating distributed Bragg reflector semiconductor laser.

2. The apparatus of claim 1 , wherein the tuning inputs of the optical source include two mirror currents and a phase current.

3. The apparatus of claim 2 , wherein the tuning inputs of the optical source further include a gain current.

4. The apparatus of claim 2 , wherein the control input of the optical source is the phase current.

5. The apparatus of claim 1 , wherein the nonzero mode-hop free wavelength range around each output wavelength is at least +/−0.3 nm.

Assignees

• Picarro Inc

Inventors

• Farinas Alejandro Dario
• Hoffnagle John A
• Rella Chris W
• Tan Sze Meng

Classifications

• G01N21/39

  using tunable lasers · CPC title

• G01J3/027

  Control of working procedures of a spectrometer; Failure detection; Bandwidth calculation · CPC title

• G01J2003/423

  Spectral arrangements using lasers, e.g. tunable · CPC title

• G01J3/10

  Arrangements of light sources specially adapted for spectrometry or colorimetry · CPC title

• G01J3/4338 Primary

  Frequency modulated spectrometry · CPC title