US 6,100,975 A · Raman spectroscopy apparatus and method using external cavity laser for continuous chemical analysis of sample streams

Abstract

Raman spectrometer for analyzing the chemical composition of sample streams using an external cavity laser light source is disclosed. The laser provides an effective light source useful in continuously analyzing a sample stream containing petroleum products, aqueous or biological fluids, or solid slurries. The light is introduced into a bundle of optical fibers connected to a Raman sample cell. The Raman sample cell is configured to allow continuous sample flow therethrough. Scattered light from the sample cell preferably exits the optical fibers as a linear optical signal. A Raman spectrometer passes the optical signal through an excitation wavelength filter, an optical slit, and a volume holographic transmission grating with an aberration correction device before transmitting the optical signal to a charge coupled device array which converts the optical signal into a electronic signal. The electronic signal is analyzed and converted by computer into a representation of the chemical analysis of the sample stream.

Claims53

Dependent claims

An external cavity laser comprising:

one or more diode laser emitters which emit light along a linear optical axis;
a collimating lens for receiving light from the one or more laser emitters, said collimating lens having a diameter sufficiently large to capture light emitting from the one or more laser emitters;
and
a retro-reflection volume holographic grating positioned along the optical axis to receive light from the collimating lens, said grating being oriented at a non-normal angle relative to the light from the collimating lens, said grating diffracting first order emitted light along the optical axis to provide optical feedback to the one or more laser emitters for frequency stabilization of the light emitted by the one or more laser emitters, wherein zeroth order emitted light passes through said grating along the optical axis as laser output.

1 more element

An apparatus for analyzing a sample using Raman spectroscopy comprising:

an external cavity laser source for producing light having an excitation wavelength, wherein the external cavity laser source comprises:
one or more diode laser emitters which emit light having an excitation wavelength along a linear optical axis;
a collimating lens for receiving light from the one or more laser emitters, said collimating lens having a diameter sufficiently large to capture light emitting from the one or more laser emitters;
and
a retro-reflection volume holographic diffraction grating positioned along the optical axis to receive light from the collimating lens, said grating being oriented at a non-normal angle relative to the light from the collimating lens, said grating reflecting first order emitted light along the optical axis to provide optical feedback to the one or more laser emitters, wherein a zeroth order emitted light passes through said grating along the optical axis as laser output;
a Raman sample cell comprising a sample stream inlet and a sample stream outlet for continuous sample flow through the sample cell;
means for directing light from the laser source into the Raman sample cell;
an optical connector for connecting one or more collection optical fibers to the sample cell for receiving scattered light from the sample cell;
a Raman spectrometer comprising:
an array of the one or more collection optical fibers for transmitting scattered light from the sample cell as an optical signal;
a filter for rejecting portions of the optical signal having the excitation wavelength;
a spectrometer grating to disperse the optical signal;
and
a light sensor for converting the optical signal into a corresponding electronic signal;
and
a computer for converting the electronic signal into a representation of the chemical analysis of the sample stream.

13 more elements

An apparatus for analyzing a sample using Raman spectroscopy comprising:

an external cavity laser source for producing light having an excitation wavelength, wherein the external cavity diode laser comprises:
one or more diode laser emitters which emit light along a linear optical axis;
a collimating lens for receiving light from the one or more laser emitters, said collimating lens having a diameter sufficiently large to capture light emitting from the one or more laser emitters;
and
a volume holographic transmission grating positioned along the optical axis to receive light from the collimating lens, said grating being oriented at a non-normal angle relative to the light from the collimating lens, said volume holographic transmission grating having a plurality of grooves oriented parallel to the one or more laser emitters;
a mirror positioned to receive first order diffracted light from the volume holographic transmission grating and to reflect said first order diffracted light back to the volume holographic transmission grating to provide optical feedback to the one or more laser emitters for frequency stabilization of the one or more laser emitters, wherein zeroth order emitted light passes through said grating along the optical axis as laser output;
a Raman sample cell comprising a sample stream inlet and a sample stream outlet for continuous sample flow through the sample cell;
means for directing light from the laser source into the Raman sample cell;
an optical connector for connecting one or more collection optical fibers to the sample cell for receiving scattered light from the sample cell;
a Raman spectrometer comprising:
an array of the one or more collection optical fibers for transmitting scattered light from the sample cell as an optical signal;
a filter for rejecting portions of the optical signal having the excitation wavelength;
a spectrometer grating to disperse the optical signal;
and
a light sensor for converting the optical signal into a corresponding electronic signal;
and
a computer for converting the electronic signal into a representation of the chemical analysis of the sample stream.

14 more elements

Dependencies are inferred from the claim text.

Raman spectroscopy apparatus and method using external cavity laser for continuous chemical analysis of sample streams

Life of this patent

Raman spectroscopy apparatus and method using external cavity laser for continuous chemical analysis of sample streams

Life of this patent

Abstract

Claims53