ADJUSTABLE EXTENDED FOCUS RAMAN SYSTEM

Abstract

An embodiment of a system is described that comprises a light source configured to produce a light beam; a collimating lens disposed on a movable mount, wherein the collimating lens is configured to capture the light beam and produce a substantially collimated beam; and an aspheric diffuse ring optic configured to receive the collimated beam and produce a spot on a surface that comprises a non-uniform radial intensity distribution.

Claims

1. A system, comprising: a light source configured to produce a light beam; a collimating lens configured to capture the light beam and produce a substantially collimated beam; and an aspheric diffuse ring optic configured to receive the collimated beam and produce a spot on a surface that comprises a non-uniform radial intensity distribution.

2. The system of claim 1, wherein: the aspheric diffuse ring optic has aspheric coefficients that comprise A1=−0.01, A2=−0.06, and A4=0.002.

3. The system of claim 1, wherein: the collimating lens is disposed on a movable mount.

4. The system of claim 3, wherein: the moveable mount is configured to translate the collimating lens up to 10 mm in distance.

5. The system of claim 3, wherein: the moveable mount is configured to adjust a relative position between the collimating lens and the aspheric diffuse ring optic to produce the spot with a diameter in a range from about 10 micron to about 10 mm.

6. The system of claim 5, wherein: the spot comprises a degree of the non-uniform radial intensity distribution, wherein the degree is associated with the diameter.

7. The system of claim 3, wherein: the moveable mount comprises a voice coil.

8. The system of claim 3, wherein: the moveable mount comprises a linear positioning assembly with micron resolution.

9. The system of claim 1, further comprising: one or more steering mirrors and one or more focusing optics configured to direct the spot onto the surface.

10. A method, comprising: producing a light beam; producing a substantially collimated beam from the light beam; and producing a spot on a surface that comprises a non-uniform radial intensity distribution from the collimated light beam.

11. The method of claim 10, wherein: changing a diameter of the spot in a range from about 10 micron to about 10 mm.

12. The method of claim 11, wherein: the spot comprises a degree of the non-uniform radial intensity distribution, wherein the degree is associated with the diameter.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0016] To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

[0017] FIG. 1 illustrates an item 100 including the optics 102, user 104, computer 108 and Raman spectrometer 106 in communication with one another.

[0018] FIG. 2 is an illustration of one embodiment of optical configuration 200 of optics 102 configured to achieve a variable focus distributed illumination spot.

[0019] FIG. 3 illustrates spot intensity distribution 300 in accordance with one embodiment.

[0020] FIG. 4 illustrates cumulative intensity plot 400 that shows the relative intensity by radius distance from a centroid in accordance with one embodiment.

[0021] FIG. 5 illustrates cumulative intensity plot 500 in accordance with one embodiment.

[0022] FIG. 6 illustrates optical arrangement 600 in accordance with one embodiment.

[0023] FIG. 7 illustrates false color spot image 700 in accordance with one embodiment.

[0024] FIG. 8 illustrates adjustable illumination spot diameter 800 in accordance with one embodiment.

DETAILED DESCRIPTION

[0025] ““traditional” Raman measurement” refers to a Raman system where the illumination spot diameter remains fixed size and has a uniform radial distribution

[0026] “Aspheric diffuse ring producing optic” refers to One embodiment for producing the distributed spot includes an aspheric diffuse ring producing optic, or ADRPO. For example, embodiments of aspheric optics may include what is referred to as an axicon or conical optic which produces a ring of intensity but has higher order aspheric terms to produce the spread-out pattern. In the described example the aspheric optic may have coefficients of A1=−0.01, A2=−0.06, and A4=0.002, with all other terms being zero.

[0027] “Collimating lens” refers to optical elements that transform the incoming light direction to parallel paths

[0028] “Filter” refers to optical elements that remove some wavelengths of incoming light

[0029] “Focusing optics” refers to optical elements that transform the incoming light direction to a point in space

[0030] “Light source” refers to A light source used for excitation in a spectroscopy application. May include a laser that is adapted for Raman spectroscopy such as 785 nm or 1064 nm. The light source could also include a broad band source such as an LED.

[0031] “Moving mount” refers to a mechanical assembly allowing an optical element to move in a linear fashion

[0032] “Non-uniform radial spot distribution” refers to an illumination area that has an intentionally varying uniformity from center to edge

[0033] “Sample surface plane” refers to the surface of the sample under test where the illumination area is directed

[0034] “Steering mirrors” refers to optical elements used to change the direction of light path

[0035] “Uniform radial spot distribution” refers to an illumination area that has a nominally consistent uniformity from center to edge

[0036] “Voice coil” refers to Voice coil actuators (VCAs) are direct drive, limited motion devices that utilize a permanent magnet field and coil winding (conductor) to produce a force that is proportional to the current applied to the coil.

[0037] The subject invention is now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It may be evident, however, that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing the present invention.

[0038] As used herein, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A, X employs B, or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances. Moreover, articles “a” and “an” as used in the subject specification and annexed drawings should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form.

[0039] Raman spectroscopy systems can be used in a variety of environments to identify unknown materials, to evaluate the threat posed by unknown materials, to provide positive identification of packaged raw materials, and to provide general security screening functions of a variety of substances. Raman spectroscopy systems can be implemented in a wide range of sizes, from portable, handheld instruments to larger systems in permanent laboratories.

[0040] As depicted in FIG. 1, user 104 interacts with Raman spectrometer 106 and computer 108 in order to take Raman spectroscopy measurements using the system. In one embodiment, computer 108 and Raman spectrometer 106 are packaged together as a portable system that can be operated on battery power for use outside a laboratory setting. The system may be a fully integrated device or may be configured as separate units for computer 108 and Raman spectrometer 106. In some embodiments, computer 108 may be located separate from Raman spectrometer 106 providing the opportunity for increased computing power at a central location. One skilled in the art can envision various interconnections, both physical and wireless, between the components of the system.

[0041] One embodiment for producing the distributed spot includes an aspheric diffuse ring producing optic, or ADRPO. For example, embodiments of aspheric optics may include what is referred to as an axicon or conical optic which produces a ring of intensity but has higher order aspheric terms to produce the spread-out pattern. In the described example the aspheric optic may have coefficients of A1=−0.01, A2=−0.06, and A4=0.002, with all other terms being zero.

[0042] Turning to FIG. 2. The optical arrangement can be manipulated in order to change the diameter of the spot. For example, moving collimating lens 204 to the left (toward the optical fiber input) by about 3.0 mm, as shown in the following diagram results in a reduction in spot diameter.

[0043] FIG. 2 description of elements: optics 102 may include optical configuration 200 with various elements coupled to light source 202 that includes any type of light source known in the art that produces a beam of light useable for Raman spectroscopy. Light source 202 may be configured for direct input to optical configuration 200, or light source 202 may be fiber optically coupled to optical configuration 200. Collimating lens 204 may be designed to optimally capture substantially all of the light from the beam output from light source 202 and produce a substantially collimated beam. Collimating lens 204 can be movably mounted such that it can change position along the axis of the optical path. For example, the range of motion in the described embodiment is about 0.1 mm to about 10 mm to allow for a change in spot size on the sample surface to range from about 10 microns to about 10 mm. Collimating lens 204 directs the substantially collimated beam into aspheric diffuse ring producing optic 208 configured to produce a light pattern that is radially diffuse. The intensity of the output from aspheric diffuse ring producing optic 208 is more intense at the outer edge of the resulting pattern than in the center. While this pattern could be projected directly onto sample surface plane 216, in practical application it is advantageous to use one or more steering mirrors 210, one or more filters 206, and focusing elements such as concave focusing lens 212 and focusing optics 214, to direct the radially diffuse light pattern onto sample surface plane 216.

[0044] FIG. 3 shows an image of spot intensity distribution 300. The non-uniform distribution shows the higher relative intensity at the outer edges than in the center (e.g. centroid). A sample output from optical configuration 200 that shows the non-uniform distribution of the spot intensity. Of particular note is that the spot still has some level of intensity in the center of the distribution that gradually increases in intensity towards the edge which has the highest level of intensity. The diameter of the spot can be controlled in a range of about 10 microns to as large as about 10 mm in diameter.

[0045] FIG. 4 is an illustrative example of plot 400 of cumulative intensity versus radius distance from a centroid out to a 750-micron radius for a 1.5 mm diameter spot. As can be seen from the plot, the central region intensity is fairly low producing an intensity that is just above background levels. The intensity rapidly increases towards the outer extents of the profile, that is referred to herein as a “diffuse ring type pattern”. The specific level of illumination at the center, as well as the characteristics of the diffuse ring curve could be altered depending on one or more characteristics of optical configuration 200 (e.g. relative distance between collimating lens 204 and aspheric diffuse ring producing optic 208) that may include the optical properties of the aspheric diffuse ring producing optic 208 (ADRPO).

[0046] FIG. 5 compares the cumulative intensity in plot 500 of a diffuse spot with a uniform spot. In a traditional Raman spectroscopy arrangement, the illumination spot is of substantially uniform intensity across its diameter. As you can see in FIG. 5, the intensity of the traditional uniform radial spot distribution 504 is substantially linear from its origin to its edge. Comparatively, aspheric diffuse ring producing optic 208 produces non-uniform radial spot distribution 502 that shows a substantially non-linear cumulative intensity from origin to edge.

[0047] FIG. 6 is an illustrative example of optical arrangement 600 wherein movement of the collimating lens 204 using collimating lens moving mount 602 effects the spot diameter. In some embodiments collimating lens moving mount 602 comprises a linear positioning assembly capable of micron resolution. In some cases, collimating lens moving mount 602 comprises a voice coil, however other types of moving mount known in the art may be employed. For example, collimating lens moving mount 602 may include a piezo, motor, or other type of linear positioning assembly known in the art.

[0048] As the distance between collimating lens 204 and aspheric diffuse ring producing optic 208 changes (e.g.—collimating lens 204 is moved relative to the position of aspheric diffuse ring producing optic 208), the spot diameter will change. For example, as the distance increases the spot diameter becomes smaller and as the distance decrease the spot diameter becomes larger.

[0049] FIG. 7 is an illustrative example (using a false color spot image 700) of the spot focused to about a 900 micron diameter using optical configuration 200, with the distance between collimating lens 204 and aspheric diffuse ring producing optic 208 configured to generate a spot with an intensity distribution that has enough uniformity for “traditional” Raman measurement. Thus, optical configuration 200 enables “traditional” Raman measurement, as well as measurements where the spot is made larger producing a more pronounced diffuse ring type pattern as the diameter increases.

[0050] FIG. 8 is an illustrative example of embodiments of the adjustable illumination spot diameter 800 comprising different diameters. A tightly focused spot 802 illustrates a substantially uniform intensity although it will be appreciated that some intensity distribution exists; medium spot 804 illustrates a discernable diffuse ring type pattern (e.g. higher degree of intensity distribution/non-uniformity than spot 802); medium-large spot 806 illustrates a more pronounced diffuse ring type pattern than medium spot 804 (e.g. higher degree of intensity distribution/non-uniformity than spot 804); and large diameter spot 808 illustrates a clearly defined diffuse ring type pattern (e.g. highest degree of intensity distribution/non-uniformity). Importantly, each of spots 802, 804, 806, and 808 maintain a degree of non-uniform radial intensity distribution at all sizes. In other words, the degree of non-uniformity of the intensity distribution is directly related to the diameter of the spot.

[0051] While the present invention has been illustrated by a description of an exemplary embodiment and while this embodiment has been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept.