All reflective apparatus for injecting excitation light and collecting in-elastically scattered light from a sample
An apparatus is disclosed wherein laser radiation illuminates a sample using all reflective optics and wherein in-elastically scattered light from the sample is collected using the identical elements. The apparatus obviates the problem of contaminating the laser radiation with unwanted spectra from transmissive optics while providing very high rejection of the laser radiation with respect to the in-elastically scattered light. In addition, the apparatus can collect and launch light with high numerical aperture and large field of view.
1. An apparatus for launching optical radiation onto a sample and for collecting in-elastically scattered radiation from a sample comprising:
a first parabolic off-axis reflector which focuses nominally collimated radiation onto a sample and collects scattered radiation from the sample;
an optical window optically located between the first reflector and the sample, the optical window configured such that radiation in-elastically scattered due to the optical window has a first spectrum that does not interfere with a second spectrum of the in-elastically scattered radiation from the sample;
at least one filter, wherein a filter nearest the first off-axis reflector reflects radiation from an optical source such that it is intercepted by the first off-axis reflector, and wherein the filter nearest the first off-axis reflector transmits in-elastically scattered radiation reflected by the first off-axis reflector,
the filter nearest the first off-axis reflector being disposed at an angle such that a beam from the optical source, prior to its incidence on the filter will not be substantially intercepted by the first off-axis reflector;
a second parabolic off-axis reflector which focuses the radiation transmitted by the filter nearest the first off-axis reflector; and
wherein the apparatus is further configured such that the radiation focused by the second parabolic off-axis reflector has not been transmitted by any transmissive optics capable of in-elastically scattering radiation other than the optical window.
2. The apparatus of claim 1 , wherein the means for focusing the radiation transmitted by the filter is a second off-axis reflector of substantially the same form as the first off-axis reflector.
3. The apparatus of claim 1 , wherein the filter nearest the first off-axis reflector is disposed at an angle between 6° and 30° with respect to a direction of the radiation from the sample after reflection by the first off-axis reflector.
4. The apparatus of claim 1 , wherein the filter nearest the first off-axis reflector has an effective index for either polarization of at least 1.50.
5. The apparatus of claim 4 , wherein the filter nearest the first off-axis reflector is constructed from a periodic structure in 2 or more dimensions and wherein the first off-axis reflector has an effective index exceeding 2.0.
6. The apparatus of claim 1 , wherein one or more additional filters are deployed further from the first off-axis reflector than the filter nearest the off-axis reflector which reflects the radiation from the optical source, each additional filter not being parallel to the first filter, and each additional filter substantially reflecting radiation having a wavelength of the optical source while passing the in-elastically scattered radiation.
7. The apparatus of claim 6 , wherein at least one filter of the one or more additional filters is deployed at a nominal angle of 0° with respect to the nominally collimated beam.
8. The apparatus of claim 1 , wherein an optical window is interposed between the sample and the first off-axis reflector.
9. The apparatus of claim 1 , wherein the difference between a wavelength of the optical source and a shortest wavelength transmitted by the filter nearest the first off-axis reflector is less than 2% of the nominal wavelength of the optical source.
10. The apparatus of claim 1 , wherein a field of view at the sample is greater than 5% of a distance from the first off-axis reflector to a focal point.
11. The apparatus of claim 1 , wherein the filter nearest the first off-axis reflector transmits no more than 0.1% of incident radiation from the optical source.