Spectrometer having a variable focus lens with a single air gap
The technology provides two or more spectrometers having uniform focal lengths that facilitate comparing spectral results obtained therefrom. The spectrometers include a collimating lens that receives light rays therethrough, a grating that is optically coupled to the collimating lens, and a focus lens that is optically coupled to the grating. The focus lens includes an outer body having a first lens set, an inner body having a second lens set, and an air gap defined between the first lens set and the second lens set. The inner body is moveable relative to the outer body to adjust a size of the air gap in order to modify a focal length of the focus lens. The inner body moves relative to the outer body to change an image size in the x-dimension. A fastener is provided to fixedly secure the inner body and the outer body.
1. A spectrometer, comprising:
a collimating lens that receives light rays therethrough that enter the spectrometer;
a grating that is optically coupled to the collimating lens; and
a focus lens that is optically coupled to the grating, the focus lens having:
a first body that includes a first lens set;
a second body that includes a second lens set;
an air gap defined between the first lens set and the second lens set, the first and second bodies being moveable relative to each other to adjust a size of the air gap in order to modify a size of a spectral image in a first dimension according to a first rate and in a second dimension according to a second rate, the first rate being different than the second rate; and
a fastener that mechanically engages the first body and the second body to prevent relative motion therebetween, the fastener being mechanically disengaged to permit relative motion between the first body and the second body.
2. The spectrometer according to claim 1 , further comprising a slit provided at an input connector, the slit being dimensioned to define a resolution for the spectrometer.
3. The spectrometer according to claim 2 , wherein the input connector is coupled to a probe having optical fibers.
4. The spectrometer according to claim 1 , wherein the grating is a volume phase holographic transmission grating that diffracts different wavelengths of light from a common input path into different angular output paths.
5. The spectrometer according to claim 1 , wherein the first and second bodies move relative to each other to stretch or compress the spectral image in an x-dimension and to provide a linear relationship between a height of the spectral image in a y-dimension and a ratio of focal lengths for the focus lens and the collimating lens.
6. The spectrometer according to claim 1 , wherein the fastener includes a screw, a pin, epoxy, a rivet, or any combination thereof.
7. The spectrometer according to claim 1 , wherein the collimating lens includes:
a first lens body that includes a third lens set;
a second lens body that includes a fourth lens set; and
an air gap defined between the third lens set and the fourth lens set, the first lens and second lens bodies being movable relative to each other to adjust a size of the air gap in order to modify a focal length of the collimating lens.
8. The spectrometer according to claim 7 , wherein the first lens and second lens bodies move relative to each other to change an image size in the y-dimension.
9. The spectrometer according to claim 7 , wherein the collimating lens further comprises a fastener that secures the first lens and second lens bodies.
10. The spectrometer according to claim 1 , further comprising a filter positioned between the collimating lens and the focus lens to remove residual laser light.
11. The spectrometer according to claim 1 , wherein the spectrometer is a Raman spectrometer.
12. A method of modifying a focal length of a focus lens for a spectrometer, the spectrometer having a collimating lens, a grating, and a focus lens that includes a first body with a first lens set, a second body with a second lens set, an air gap defined between the first lens set and the second lens set, the first and second bodies being moveable relative to each other, and a fastener that mechanically engages the first body and the second body to prevent relative motion therebetween, the method comprising:
moving the first body relative to the second body to adjust a size of an air gap provided between the first lens set and the second lens set;
reducing the size of the air gap to compress a spectral image in a first dimension;
increasing the size of the air gap to stretch the spectral image in the first dimension; and
adjusting the size of the air gap to modify a ratio of focal lengths for the focus lens and the collimating lens, the ratio determining a size of the spectral image in a second dimension.
13. The method according to claim 12 , further comprising mechanically engaging the first body and the second body with the fastener.
14. The method according to claim 12 , wherein the first dimension is the x-dimension.
15. The method according to claim 12 , wherein the second dimension is the y-dimension.
16. The method according to claim 12 , wherein the spectral image is a two dimensional image.