Probe assemblies for Raman spectroscopy

• US 20040160601A1
• Filed: 02/14/2003
• Published: 08/19/2004
• Est. Priority Date: 02/14/2003
• Status: Active Grant

• Current Assignee: Raman Systems, Inc.
• Original Assignee: Raman Systems, Inc.
• Inventors: Clarke, Richard H., Womble, M. Edward
• Granted Patent: US 6,897,951 B2
• Time in Patent Office: Days
• US Class Current: 356/301
• CPC Class Codes: G01J 3/44 Raman spectrometry; Scattering spectrometry ; Fluorescence spectrometry
• CPC Class Codes: G01N 21/276 with alternation of sample and standard in optical path
• CPC Class Codes: G01N 21/65 Raman scattering
• CPC Class Codes: G01N 2201/06113 Coherent sources; lasers
• CPC Class Codes: G01N 2201/08 Optical fibres; light guides

Abstract

Raman spectroscopy probe assemblies are disclosed for use with portable and/or handheld analyzers. The probes are also adaptable to sample liquids, and/or powders, tablets and/or other solids and are capable of withstanding harsh environmental conditions. The probes include an optical head assembly, associated optical fibers and replaceable sampling tubes. Safety shut-off mechanisms are provided to reduce the risk of inadvertent exposure to radiation. In one embodiment, the shut-off switch is a spring-biased shutter that is opened by a solenoid only under predefined proper operating conditions. In another aspect of the invention, a simple orthogonal optical head assembly is disclosed that does not require collinear optical paths. The orthogonal arrangement of input and captured light paths also reduces the need for precise alignment of the optical components. The orthogonal optical head assemblies of the present invention are well suited to accommodate the shutoff mechanisms of the present invention. The open architecture of the orthogonal assembly also facilitates the placement of lenses and/or filters within the head assembly, and also accommodates other elements, such as energy absorbing chambers, within the head assembly. In another aspect of the invention, sampling tubes, and replaceable end caps for such tubes, are disclosed that facilitate hand measurements of substances.

Claims

1. A Raman spectrometer probe comprising:

an input fiber through which radiation can propagate to irradiate a sample;

a collection fiber through which radiation scattered by the sample can be coupled to a detector;

an optical head assembly defining an input path and an output path, wherein the input path comprises at least one light directing element that receives excitation radiation from the input fiber and directs it to the sample and the output path further includes at least light collecting element that collects radiation scattered by the sample and couples the scattered radiation into the collection fiber; and

a shut-off switch disposed along the input path of the optical head assembly including a shutter for blocking passage of excitation radiation through the optical head assembly when the probe is not in use.

2. The probe of claim 1 wherein the shutter is spring-biased in a closed position.

3. The probe of claim 2 wherein the shutter is opened by a solenoid.

4. A Raman spectrometer probe comprising:

an input fiber through which radiation can propagate to irradiate a sample;

a collection fiber through which radiation scattered by the sample can be coupled to a detector;

an optical head assembly defining an input path and an output path, wherein the input path comprises at least one light directing element that receives excitation radiation from the input fiber and directs it to the sample and the output path further includes at least light collecting element that collects radiation scattered by the sample and couples the scattered radiation into the collection fiber; and

wherein the input and output paths of the head assembly are substantially orthogonal and the head assembly further comprises a dichroic mirror that directs the excitation radiation to the sample by reflection and transmits scattered radiation returning from the sample to the output path.

5. The probe of claim 4 wherein the optical head assembly further comprises a shutter for blocking the input path when the probe is not in use.

6. The probe of claim 4 wherein the shutter is spring-biased in a closed position.

7. The probe of claim 5 wherein the shutter is opened by a solenoid.

8. The probe of claim 4 wherein the light directing element comprises a collimating lens disposed in the input path.

9. The probe of claim 4 wherein the optical head assembly further comprises an input optical filter disposed in the input path.

10. The probe of claim 9 where the filter is a short-pass filter.

11. The probe of claim 4 wherein the probe further comprises a sampling tube defining collinear input and output beam paths for transmitting light to a sample and collecting light scattered by the sample.

12. The probe of claim 11 where the sampling tube further comprises at least one lens element for transmitting light to a sample and collecting light scattered by the sample.

13. The probe of claim 4 wherein the optical head assembly further comprises an output optical filter disposed in the output path.

14. The probe of claim 11 where the filter is a long-pass filter.

15. The probe of claim 4 wherein the light collecting element comprises a focusing lens for focusing collect light into the output fiber.

16. The probe of claim 15 wherein the lens element allows both the multi-mode radiation to pass through to a focal point on the sample and the scattered radiation to pass from the sample without substantially contacting the interior wall of the tubular structure.

17. The probe of claim 15 wherein the sampling tube further includes a removable end cap.

18. The probe of claim 17 wherein the end cap includes a fluid impervious window.

19. The probe of claim 17 wherein sampling tube further comprises at least one seal for the end cap.

20. The probe of claim 17 wherein the end cap includes a calibration material.

21. The probe of claim 4 wherein the optical head assembly further comprises an beam energy dump for absorbing radiation from the input path that is not reflected by the dichroic mirror.

22. A method for detecting or quantifying a chemical constituent in a sample using a Raman spectroscopy probe comprising:

providing a probe comprising an excitation fiber, a collection fiber, an optical head assembly and a sampling tube through which multi-mode radiation can propagate, the excitation fiber having a first end optically coupled to a multi-mode laser, and a second end positioned in optical alignment with the head assembly and the sampling tube to allow both the multi-mode radiation to pass through to a focal point on the sample and the scattered radiation to pass from the sample to the collection fiber;

placing the probe in proximity to the sample;

activating the multi-mode laser to irradiate the sample to produce a Raman spectrum consisting of scattered electromagnetic radiation;

collecting a portion of the scattered radiation;

separating the collected radiation into different wavelength components using a low resolution dispersion element;

detecting at least some of the wavelength components of the scattered light using a detection array; and

processing the data from the detection array to detect the presence or quantity of an chemical constituent in a sample.

23. The method of claim 22, wherein the step of separating and collecting the radiation comprises having a resolution of between 30 cm and 50 cm, wherein the resolution is determined in part by the multi-mode laser and, in part by the dispersion element.

24. The method of claim 22 wherein the method further comprises disposing a safety switch within the optical head assembly.

25. The method of claim 24 wherein the safety switch is disposed in as normally-closed position within the optical head assembly to block passage of excitation radiation to the sample.