Parabolic focusing apparatus for optical spectroscopy

Abstract

An accessory for use in the sample region of a spectrometer is disclosed which combines a matched pair of off-axis paraboloid reflectors having their focii optically imaged on the sample (either imaged at a common point or at two points which are optically imaged on each other) and having relative locations and orientations such that each ray of radiation strikes the two reflectors at points on the reflectors having approximately the same focal lengths. This arrangement involves the use of collimated optical beams into and out of the accessory. The accessory may function as a transmission-type accessory, in which the radiation passes through the sample, or as an internal reflectance accessory, in which the radiation passes through the sample holder but is reflected by the sample. The focal length relationship set forth is accomplished by having the "back-to-back" paraboloid reflectors, i.e., their reflecting surfaces face in substantially different, preferably opposite, directions. A further aspect is the incorporation of means for adjusting the position of at least one of the paraboloid reflectors along a first line parallel to, and along a second line perpendicular to, the axis of the collimated optical beam reflected by the position-adjustable reflector.

What is claimed is: 
     
       1. For use with a spectrometer having a collimated radiation beam approaching a sample and a collimated radiation beam leaving the sample, an optical accessory, of the type in which radiation is passed through a sample holder element which provides a confined path therethrough, comprising: a first paraboloid reflector which reflects the approaching collimated beam in such a way as to focus the radiation at one end of the confined radiation path through the sample holder;   a second paraboloid reflector which receives radiation from a focus at the other end of the radiation path through the sample holder and which reflects the radiation to provide the collimated beam leaving the sample; and   means for allowing constrained .Iadd.translational .Iaddend.adjustment movement of at least one of the paraboloid reflectors relative to the other paraboloid reflector in order to adjust for differences in the length and/or orientation of the sample holder element, such means including (a) means for allowing such movement of at least one of the paraboloid reflectors along a path parallel to the axis of its incident collimated beam, and (b) means for allowing such movement of at least one of the paraboloid reflectors along a path perpendicular to the axis of its incident collimated beam.   
     
     
       2. The optical device of claim 1 in which the collimated radiation beams approaching and leaving the sample are co-linear, and in which only one of the two paraboloid reflectors is allowed constrained adjustment movement, the optical accessory also comprising: a first flat reflecting mirror which laterally reflects the collimated beam reflected by the movable paraboloid;   a second flat reflecting mirror which reflects the collimated beam from the first reflecting mirror to cause the approaching and leaving beams to be co-linear;   a first supporting member which carries the first reflecting mirror;   a second supporting member which carries the second reflecting mirror; and   linear guiding means between the first and second supporting members which permits relative movement of the two flat mirrors constrained to linear movement along the axis of the collimated beam which travels between them.   
     
     
       3. The optical device of claim 2 wherein: the first flat reflecting mirror and the movable paraboloid reflector are both mounted on the first supporting member in positions which remain fixed relative to one another;   the first supporting member and the second flat reflecting mirror are both carried by the second supporting member;   the first supporting member is linearly movable on the second supporting member along the axis of the collimated beam between the first and second flat reflecting mirrors; and   the second supporting member is linearly movable along the axis of the collimated co-linear approaching and leaving beams.   
     
     
       4. The optical accessory of claim 2 wherein: the second flat reflecting mirror remains in a fixed position on the second supporting member;   the first flat reflecting mirror and the movable paraboloid reflector are both mounted on the first supporting member; and   the movable paraboloid reflector is linearly movable for adjustment purposes on the first supporting member along the axis of the collimated beam between the movable paraboloid reflector and the first flat reflecting mirror.   
     
     
       5. .[.The optical accessory of claim 1 in which the means for allowing constrained adjustment movement comprises:.]. .Iadd.For use with a spectometer having a collimated radiation beam approaching a sample and a collimated radiation beam leaving the sample, an optical accessory, of the type in which radiation is passed through a sample holder element which provides a confined path therethrough, comprising: a first paraboloid reflector which reflects the approaching collimated beam in such a way as to focus the radiation at one end of the confined radiation path through the sample holder;   a second paraboloid reflector which receives radiation from a focus at the other end of the radiation path through the sample holder and which reflects the radiation to provide the collimated beam leaving the sample; and   means for allowing constrained adjustment movement of at least one of the paraboloid reflectors relative to the other paraboloid reflector in order to adjust for differences in the length and/or orientation of the sample holder element, such means including (a) means for allowing such movement of at least one of the paraboloid reflectors along a path parallel to the axis of its incident collimated beam, and (b) means for allowing such movement of at least one of the paraboloid reflectors along a path perpendicular to the axis of its incident collimated beam;   the means for allowing constrained adjustment movement comprising: .Iaddend.   a first linearly extending guide parallel to the axis of the collimated beam reflected by the movable paraboloid reflector, along which guide the position of the movable paraboloid reflector may be adjusted; and   a second linearly extending guide perpendicular to the axis of the collimated beam reflected by the movable paraboloid reflector, along which guide the position of the movable paraboloid reflector may be adjusted. .Iadd.   
     
     
       6.  In a spectrometer having a collimated radiation beam approaching a sample region, and a collimated radiation beam leaving the sample region, a sample-illuminating optical system comprising: a first paraboloid reflector which reflects the approaching collimated beam in such a way as to focus the radiation at the sample;   a second paraboloid reflector which receives radiation from the sample and which reflects that radiation to provide the collimated beam leaving the sample region; and   means for allowing constrained translational adjustment movement of at least one of the paraboloid reflectors relative to the other paraboloid reflector, such means including (a) means for allowing such movement of at least one of the paraboloid reflectors along a first path, and (b) means for allowing such movement of at least one of the paraboloid reflectors along a second path perpendicular to the first path. .Iaddend. .Iadd.   
     
     
       7.  The optical system of claim 6 in which one of the two paraboloid reflectors is allowed constrained adjustment movement, the optical system also comprising: a flat reflector which reflects the collimated beam received from the movable paraboloid reflector;   means for providing linear adjusting movement of the paraboloid reflector relative to the flat reflector; and   means for providing parallel linear adjusting movement of the paraboloid reflector and the flat reflector. .Iaddend. .Iadd.8. The optical system of claim 7 which comprises:   a first supporting member which carries the movable paraboloid reflector, but not the flat reflector; and   a second supporting member which carries both the movable paraboloid reflector and the flat reflector;   the first supporting member being linearly movable on the second supporting member along the axis of the collimated beam. .Iaddend. .Iadd.9. The optical system of claim 6 in which the means for allowing constrained adjustment movement comprises:   a first linearly extending guide parallel to the axis of the collimated beam reflected by the movable paraboloid reflector, along which guide the position of the movable paraboloid reflector may be adjusted; and   a second linearly extending guide perpendicular to the axis of the collimated beam reflected by the movable paraboloid reflector, along which guide the position of the movable paraboloid reflector may be adjusted. .Iaddend. .Iadd.10. The optical system of claim 6 which also comprises:   a flat reflector which reflects one of the two collimated beams; and   means for providing parallel linear motion of one of the two paraboloid reflectors and the flat reflector. .Iaddend. .Iadd.11. The optical system of claim 10 which also comprises:   a movable platform on which are mounted both the flat mirror and the paraboloid reflector having parallel motion. .Iaddend. .Iadd.12. The optical system of claim 11 in which the platform is constrained to move in a direction parallel to the collimated beam entering or leaving the flat reflector. .Iaddend. .Iadd.13. In an analytical instrument of the type having a source of analytical radiation, having means for detecting said radiation, and having means for supporting a sample to be analyzed; an improved sample-illuminating system comprising:   pre-sample optical focusing means for focusing analytical radiation to illuminate the sample;   post-sample optical collimating means for receiving and collimating output analytical radiation after it has illuminated the sample; and   supporting means for the post-sample collimating means which allows translational adjustment of the position of said collimating means constrained to two directions which are parallel or perpendicular to the   
     
     
        axis of its collimated output beam. .Iadd.14.  The optical system of claim 13 in which the supporting means comprises: a first guiding means for said post-sample collimating means which allows adjustment of its position constrained to a direction parallel to its collimated output beam; and   a second guiding means for said post-sample collimating means which allows adjustment of its position constrained to a direction perpendicular to its collimated output beam. .Iaddend. .Iadd.15. The optical system of claim 13 in which the pre-sample focusing means and the post-sample collimating means comprises reflecting elements. .Iaddend. .Iadd.16. The optical system of claim 15 in which the reflecting elements are parabolic mirrors whose focal points are in the sample region. .Iaddend. .Iadd.17. In an analytical instrument of the type having a source of analytical radiation, having means for detecting said radiation, and having means for supporting a sample to be analyzed; an improved sample-illuminating system comprising:   pre-sample optical focusing means for focusing analytical radiation to illuminate the sample;   post-sample optical collimating means for receiving and collimating output analytical radiation after it has illuminated the sample; and   supporting means for one of the optical means which provides for constrained adjustment movement of said optical means along two purely translational paths. .Iaddend.