US20100296085A1

US20100296085A1 - Raman spectrometry assembly

Info

Publication number: US20100296085A1
Application number: US12/763,778
Authority: US
Inventors: Masud Azimi; Kevin J. Knopp; Steve McLaughlin
Original assignee: Ahura Scientific Inc
Current assignee: Thermo Scientific Portable Analytical Instruments Inc
Priority date: 2006-08-22
Filing date: 2010-04-20
Publication date: 2010-11-25
Also published as: US7701571B2; US20090033928A1

Abstract

A Raman spectrometry assembly includes a Raman spectrometer having a laser light source and a Raman signal analyzer, an interface module comprising a housing which is connectable to and disconnectable from the spectrometer, and a fiber optic assembly which is connectable to and disconnectable from the interface module, the fiber optic assembly including optical fibers and a probe head at a distal end thereof for disposition adjacent a specimen to be tested, the optical fibers extending from the probe head and adapted to extend to the interface module.

Description

REFERENCE TO PENDING PRIOR PATENT APPLICATION

This patent application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/839,188 filed Aug. 22, 2006, in the names of Masud Azimi, Kevin Knopp and Steve Mclaughlin.

BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to apparatus for identifying and characterizing substances using Raman spectroscopy, which provides a non-contact and non-invasive technique for investigation and analysis of chemical substances.
2. Description of the Prior Art
Raman spectroscopy is widely used in the scientific, commercial and public safety areas.
Technological advances are making it possible to increase the range of applications using Raman spectroscopy, through reductions in costs and size of the equipment. Portable units have become available for field uses, such as on-site identification of potentially hazardous materials.
In applications of Raman spectroscopy, it is generally desirable to bring an optical probe to a position adjacent a specimen. This can be a problem in view of the potentially hazardous materials which are to be analyzed, including explosives, chemical agents, toxic industrial chemicals, and the like. In some applications, it is required, for safety reasons, that delivery of laser light to a specimen under test, and a collection of Raman signal from the specimen, be done at a location remote from the Raman spectrometer hardware. Optical fiber, which can serve as a conduit for laser light and Raman signal light, is a good medium for achieving this. However, there are some problems in the use of optical fibers and probes for Raman spectroscopy.
Firstly, the distal end of the probe can become contaminated during data collection and it is often desirable, and at times necessary, to replace the probe head, which is very costly, if it can be done at all. Accordingly, there is a need for a relatively inexpensive optical fiber assembly, including optical fiber and a probe head, which can be disconnected from the spectrometer and replaced with another optical fiber assembly.
Secondly, propagation of a high power laser light within an optical fiber generates unwanted Raman signal from the optical fiber material itself which adds to the Raman signal collected from a specimen and, in many cases, is difficult to distinguish from the specimen signal and difficult to subtract from the Raman signal generated from the specimen under test.
Accordingly, there is a further need for means for preventing Raman signals generated by the material of an excitation fiber of an optical fiber assembly from reaching the specimen under test, such that only the excitation laser signal reaches the specimen and the Raman signals received from the specimen and conducted to a spectrometer by way of a collection fiber of the optical fiber assembly are from the specimen only and not from the excitation fiber.
Thirdly, the laser light exiting the distal end of the excitation fiber diverges immediately and does so until the excitation light reaches the specimen under test. Thus, the portion of the excitation light which reaches the specimen reduces, increasingly, as the distance between the excitation fiber and the specimen increases.
There is accordingly a still further need for means to focus the light from the excitation fiber onto a small area of the specimen. Similarly, Raman signals reflected off the specimen diverge outwardly from the specimen with only a small portion of the reflected light reaching an end of a collection fiber. Accordingly, there is also a need for means to focus Raman light from a specimen onto the small area of an end of a collection fiber.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide a Raman Spectrometry Assembly in which a fiber optic assembly, including a probe head and optical fibers, is detachable from a Raman spectrometer and readily replaced with the same or another fiber optic assembly.
A further object of the invention is to provide such a fiber optic assembly in which the laser light from the spectrometer carried by the excitation fiber does not interfere with Raman signal generated by the material of the excitation fiber, such that substantially only the excitation laser impinges upon the specimen and the Raman signal reflected therefrom includes only Raman signal from the specimen.
A still further object of the invention is to provide such a fiber optic assembly in which laser light emanating from the excitation fiber distal end is focused on a small portion of the sample under test, and diverging Raman signal light reflected off the sample is focused so as to enter an end of the collection fiber for transmission to the Raman signal analyzer.
With the above and other objects in view, a feature of the present invention is the provision of a Raman spectrometry assembly, the assembly including a Raman spectrometer comprising a laser light source and a Raman signal analyzer, an interface module comprising a housing which is attachable to and detachable from the spectrometer, and a fiber optic assembly which is attachable to and detachable from the interface module, the fiber optic assembly comprising a probe head portion at a distal end thereof for disposition adjacent a specimen to be tested, and optical fibers extending from the probe head and adapted to extend to the interface module.
In accordance with a further feature of the invention, there is provided a Raman spectrometer assembly, the assembly including a Raman spectrometer comprising a laser light source and a Raman signal analyzer, a housing for releasable connection to the spectrometer, and having first and second openings extending through a wall thereof, first and second sleeves disposed in the first and second openings, a fiber optic assembly comprising first and second ferrules adapted for insertion into and withdrawal from the sleeves, an elongated excitation fiber fixed to and extending from the first ferrule and an elongated collection fiber fixed to and extending from the second ferrule, distal ends of the fibers being fixed in a probe head portion of the fiber optic assembly, and light manipulating components disposed in the housing and adapted to guide laser light to the first ferrule and thence to the excitation fiber, and to guide Raman signature light from a specimen under test to the second ferrule and thence to the Raman signal analyzer, wherein the ferrules are readily withdrawable from the sleeves and replaceable therein or by other ferrules.
In accordance with a still further feature of the invention, there is provided a Raman spectrometry assembly, the assembly including a Raman spectrometer comprising a laser light source and a Raman signal analyzer, an interface module adapted for connection to and disconnection from the spectrometer, and having a first opening extending through a wall thereof, light manipulating components disposed in the interface module for directing a laser beam emitted from the laser light source of the spectrometer toward the first opening, a first focusing lens mounted in the interface module and aligned with the first opening, and a first sleeve disposed in the first opening. The spectrometer assembly further includes a fiber optic assembly comprising a first ferrule adapted for insertion into the first sleeve and adapted for removal therefrom, the first ferrule being further adapted to reside in the sleeve and therein to receive and transmit the laser light emitted from the laser light source and the laser light directing components to an excitation fiber proximal end fixed to the first ferrule, an elongated excitation fiber extending from the proximal end thereof fixed in the first ferrule to a distal end thereof fixed in a portion of a probe head, a collection fiber extending from the probe head to a second ferrule which is removably disposed in a second sleeve disposed in a second opening in a wall of the interface module. The interface module further comprises a second focusing lens aligned with the second opening and adapted to pass collection fiber light therethrough and toward a portion of the light directing components to the Raman signal analyzer of the spectrometer. The ferrules are removable from the sleeves, and the sleeves are adapted to receive further ferrules of a configuration substantially identical to the first ferrule and the second ferrule, wherein the fiber optic assembly may readily be replaced by another fiber optic assembly.
In accordance with a still further feature of the invention, there is provided a Raman spectrometry assembly, the assembly including a Raman spectrometer comprising a laser light source and a Raman signal analyzer, an interface module adapted to pass laser light therethrough and into a flexible excitation fiber connected to the module, and adapted to pass Raman signal light from a flexible collection fiber connected to the interface module therethrough to the Raman signal analyzer, and a fiber optic assembly comprising the excitation fiber and the collection fiber, a flexible elongated protective shielding disposed around the excitation fiber and the collection fiber, and a probe head at a distal end thereof for disposition adjacent a sample to be tested, the excitation and collection fibers being adapted to extend from the probe head to the interface module, and a band pass filter at the distal end of the excitation fiber to prevent passage of laser light therethrough, but block passage of Raman signal light in the excitation fiber derived from the excitation fiber, such that the Raman signal light generated in the excitation fiber is prevented from reaching the sample.
In accordance with a still further feature of the invention, there is provided a Raman spectrometry assembly, the assembly including a Raman spectrometer comprising a laser light source and a Raman signal analyzer, an interface module comprising a housing which is connectable to and disconnectable from the spectrometer, and a fiber optic assembly which is connectable to and disconnectable from the interface module, the fiber optic assembly comprising a probe head portion at a distal end thereof for disposition adjacent a specimen to be tested, and optical fibers extending from the probe head and adapted to extend to the interface module, the optical fibers including an excitation fiber for transmitting laser light from the interface module to a specimen under test, and a collection fiber for transmitting Raman signal light from the specimen to the interface module, and a lens aligned distally of the distal ends of the optical fibers, the lens being adapted to intercept diverging laser light emanating from the excitation fiber and focus the laser light on a reduced area of the specimen, and to intercept a Raman signal light reflected from the specimen and focus the Raman signal light onto the distal end of the collection fiber.
In accordance with a still further feature of the invention, there is provided a method for obtaining an analysis of a specimen, the method comprising the steps of providing a Raman spectrometer having a laser light source and a Raman signal analyzer, providing an interface module which is adapted for attachment to the spectrometer, the module having therein light manipulating devices for directing laser light and Raman signal light for effecting excitation of the specimen and collection and directing of Raman signal light to the Raman signal analyzer, and providing a fiber optic assembly comprising an excitation fiber, a collection fiber, and a probe head, attaching the interface module to the spectrometer, attaching the fiber optic assembly to the interface module, placing the probe head adjacent the specimen, and energizing the laser light source, whereby to cause laser light to pass from the spectrometer to the interface module and therein to be directed by the light manipulating devices to the excitation fiber and the probe head and onto the specimen, and thence to pass Raman signal light back through the collection fiber to the interface module wherein the manipulating devices direct the Raman signal light to the spectrometer Raman light analyzer.
In accordance with a still further feature of the invention, there is provided a Raman spectrometry assembly including a Raman spectrometer comprising a laser light source and a Raman signal analyzer, an interface module, and a fiber optic assembly connectable to and disconnectable from the interface module. The fiber optic assembly includes a probe head at a distal end thereof for disposition adjacent a specimen to be tested, and optical fibers extending from the probe head and adapted to extend to the interface module. The optical fibers include an excitation fiber for transmitting laser light from the interface module to a specimen under test, and a collection fiber for transmitting Raman signal light from the specimen to said interface module. The probe head assembly includes first and second lenses aligned distally of distal ends of the optical fibers, the first lens being adapted to intercept diverging laser light emanating from the excitation fiber and collimate the laser light, and the second lens being adapted to intercept a Raman signal light reflected from the specimen and focus the Raman signal light onto a distal end of the collection fiber. The assembly further includes a band pass filter at the distal end of the probe head and adapted to suppress Raman signal generated by excitation fiber material and prevent such signal from reaching the specimen, a reflector for redirecting filtered laser light to a notch filter, wherein the notch filter is disposed in the probe head and is adapted to transmit Raman signal light emanating from the specimen and to block laser light reflected back from the specimen from reaching the distal end of the collection fiber, and a focusing lens disposed at the distal end of the probe head, and adapted to focus the laser light on a reduced area of the specimen, and further adapted to collect Raman signal light generated and reflected from the sample and direct the reflected light toward the distal end of the collection fiber. The assembly still further includes a water-sealed enclosure made of a selected one of metal, plastic, ceramic material and any chemically inert material, to house components of the probe head assembly.
The above and other features of the invention, including various novel details of construction and combinations of parts and method steps, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular devices and method embodying the invention are shown by way of illustration only and not as limitations of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made to the accompanying drawings in which are shown illustrative embodiments of the invention from which its novel features and advantages will be apparent.

In the drawings:

FIG. 1 is a schematic illustration of one form of spectrometry assembly illustrative of an embodiment of the invention;

FIG. 2 is a diagrammatic perspective view of a probe head portion of a fiber optic assembly of FIG. 1;

FIG. 3 is a side elevational of the probe head portion of FIG. 2;

FIG. 4 is a schematic illustration of a further portion of the spectrometry assembly of FIG. 1; and

FIG. 5 is a schematic illustration of an alternative embodiment of the probe head portion.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, it will be seen that an illustrative Raman spectroscopy assembly 20 includes a Raman spectrometer 22 including a laser light source LS and a light analyzer LA, as is known in the art.
The assembly 20 further includes an interface module 24 comprising a housing 26 which is connectable to, and disconnectable from, the spectrometer 22, and a fiber optic assembly 27 which is connectable to, and disconnectable from, the interface module 24.
Mounted in the housing 26 are light manipulating devices 28 arranged so as to receive laser light 30 from the spectrometer 22 and direct the laser light, finely focused, to a first ferrule 32 of the fiber optic assembly 27. The light manipulating devices 28 are further arranged to receive Raman signal light and direct the Raman signal light to the light analyzer LA of the spectrometer 22.
In the embodiment shown in FIG. 1, the particular light manipulating devices 28 include a notch filter 34 which directs laser light 30 a toward a reflector 36 which directs the laser light 30 b through a focusing lens 38 which focuses the light 30 b onto a fine point 40 on an inner end 42 of the ferrule 32.
In the fiber optic assembly 27, ferrule 32 has fixed thereto a flexible excitation fiber 44 housed in a flexible protective shielding 46. A distal end 48 of the laser fiber 44 is held in a probe head 50.
The housing 26 is provided with two openings 52, 54 extending through a wall 56 thereof. Flanged sleeves 60, 58 are fixed in openings 52, 54, respectively. The ferrule 32 of the fiber optic assembly 27 is insertable into, and removable from the fixed sleeve 60 of the housing 26. Similarly, a second ferrule 62 of the fiber optic assembly 27 is insertable into, and removable from, the fixed sleeve 58 of the housing 26.
The ferrule 62 has fixed thereto a collection fiber 64 which is housed in the protective shielding 46, alongside the excitation fiber 44. A distal end 66 of the collection fiber 64 is held in the probe head 50.
A collimating lens 68 is aligned with the collection fiber ferrule 62 and directs Raman signal light 70 through the notch filter 34 and into the spectrometer 22, and in particular the light analyzer LA.
While a specific arrangement of light manipulating devices 28 has been shown and described, it will be apparent that any suitable arrangement of light manipulating devices could be used to direct excitation laser light therethrough to the excitation fiber and to receive Raman signal light by way of the collection fiber 64 and direct the Raman signal light to the light analyzer of the spectrometer.
If, in use, any part of the fiber optic assembly 27, such as the probe head 50 and/or protective shielding 46 becomes contaminated, the ferrules 32, 62 may simply be “unplugged” from the sleeves 60, 58, and replaced with another optical fiber assembly, including a new probe head.
Both the fiber optic assembly, and the interface module can be readily removed from the spectrometer. Any selected releasable mechanical connection means can be used to attach the interface module to the spectrometer, including snap-on, clamp-on, screw-on, slide-and-lock-on arrangements, and the like.
Referring to FIGS. 2 and 3, it will be seen that the probe head 50 may be shaped such that the geometry of the area of the specimen S which is impacted can be predetermined. As shown in FIGS. 1 and 2, an end facet 74 of the excitation fiber 44 can be at an angle to the end 66 of the collection fiber 64.
As shown in FIGS. 2 and 3, the laser light 80 emitted from the distal end 48 of the excitation fiber 44 is in a cone configuration 82. Light reflected from the specimen S, that is, the Raman signal light 70, travels back in a cone-shaped path 84 towards the distal end 66 of the collection fiber 64 and also disperses outwardly from the path 84 and is lost. The amount of collected Raman signal depends in large measure on the geometry of the design of the probe head 50 and particularly on the cone overlap area 86 effected by the two fibers 44, 64.
Referring to FIG. 4, it will be seen that the fiber optic assembly may include a lens 72 disposed adjacent the probe head distally of the distal ends of the excitation fiber 44 and the collection fiber 64. Alternatively, the lens 72 may be used as a separate component spaced from the probe head 50. Emerging from the distal end 48 of the excitation fiber 44, the laser light 30 diverges. The lens 72 focuses the light 30 on a small area of the specimen S under test. The reflected Raman signature light 70 similarly diverges, but is focused by the lens 72 onto the distal end 66 of the collection fiber 64. Thus, relatively little Raman signal is lost compared to the extensive loss realized in the arrangement shown in FIG. 2.
Referring again to FIGS. 1-3, it will be seen that the distal end 48 of the excitation fiber 44 may be covered with a thin fiber band pass filter 90 which transmits only laser light and rejects Raman signals which may be generated by the excitation fiber. Thus, the Raman signal light 70 includes substantially only Raman signal from the specimen S and essentially none from the excitation fiber.
Referring to FIG. 5, it will be seen that in an alternative embodiment, the fiber optic assembly probe head 50 includes first and second lenses 72 a and 72 b aligned distally of distal ends of the optical fibers 44, 64, the first 72 a of the lenses being adapted to intercept diverging laser light emanating from the excitation fiber 44 and collimate the laser, and the second 72 b of the lenses being adapted to intercept a Raman signal light 70 reflected from the specimen S and focus the Raman signal light onto the distal end 66 of the collection fiber 64. A band pass filter 92 is adapted to suppress Raman signal generated by the excitation fiber material and prevent such signal from reaching the specimen. A reflector 94 redirects the filtered laser light to a notch filter 96. The notch filter 96 is disposed in the probe head and is adapted to transmit Raman signal light emanating from the specimen and to block laser light reflected back from the specimen from reaching the distal end 66 of the collection fiber 64. A focusing lens 98 is disposed at the distal end of the probe head 50, the focusing lens 98 being adapted to focus the laser light on a reduced area of the specimen S, and further adapted to collect Raman signal light generated and reflected from the sample, and direct the reflected light toward the distal end 66 of the collection fiber 64. A water-sealed enclosure 100, made of a selected one of metal, plastic, ceramic material and any chemically inert material, serves to house components of the probe head 50.
There is thus provided a spectrometer assembly comprising a spectrometer, an interface module, and a fiber optic assembly, each connectable to and disconnectable from another. In the event of contamination or damage to the fiber optic assembly, it can be easily withdrawn from the interface module and replaced. The interface module may similarly be separated from the spectrometer and the probe head assembly and replaced with a module containing a different arrangement of light manipulation devices.
There is further provided a fiber optic assembly in which the probe head projects substantially only laser light, not mixed with Raman signature light.
There is still further provided a fiber optic assembly having, or in combination with, a lens which accepts diverging laser light exiting an excitation fiber and focuses the laser light on a limited area of a specimen under test, and which accepts diverging Raman signal light from the specimen and focuses the Raman light on a distal end of a collection fiber.
The above-described assembly may be used to obtain a Raman analysis in accordance with a method including the steps of providing the Raman spectrometer 22 having the laser light source and the Raman signal analyzer, providing the interface module 24 which is adapted for attachment to the spectrometer 22, the module 24 having therein light manipulating devices 28 for directing laser light and Raman signal light for effecting excitation of the specimen and collection and directing of Raman signal light to the Raman signal analyzer, and providing the fiber optic assembly 27 comprising the excitation fiber 44, the collection fiber 64, and the probe head 50, attaching the interface module 24 to the spectrometer 22, attaching the fiber optic assembly to the interface module 24, placing the probe head 50 adjacent the specimen S, and energizing the laser light source LS, whereby to cause laser light to pass from the spectrometer 22 to the interface module 24 and therein to be directed by the light manipulating devices 28 to the excitation fiber 44 and the probe head 50 and onto the specimen S, and thence Raman signal light back through the collection fiber 64 to the interface module 24 wherein the manipulating devices 28 direct the Raman signal light to the spectrometer Raman light analyzer LA.
The method preferably includes the further step of providing the focusing lens 72 between the fiber distal ends 48, 66 and the specimen S, such that Raman signal light from the specimen is focused on the distal end 66 of the collection fiber 64.
It is to be understood that the present invention is by no means limited to the particular construction and method steps disclosed and/or shown in the drawings, but also comprises any modification or equivalent within the scope of the claims.

Claims

1. A Raman spectrometry assembly comprising:

a Raman spectrometer comprising a laser light source and a Raman signal analyzer;

an interface module comprising a housing which is connectable to and disconnectable from said spectrometer; and

a fiber optic assembly which is connected to and disconnectable from said interface module, said fiber optic assembly comprising a probe head portion at a distal end thereof for disposition adjacent a specimen to be tested, and optical fibers extending from said probe head portion and adapted to extend to said interface module.

2-26. (canceled)