Abstract Optical apparatus for use with an infrared spectrophotometer for attenuated total reflectance measurements of solid samples and, in particular, microgramme size samples includes an optical prism, bounded by plane and/or curved lateral faces, for internally reflecting a focused beam of infrared radiation incident substantially normal to a lateral face of the prism, the lateral faces of the prism being relatively disposed such that the beam is reflected by successive total internal reflections and describes a plurality of noncoincident cyclic tracks within the prism before being incident at a lateral face at an angle less than the critical angle and emerging from the prism, sample for absorptiometric analysis being applied to at least one reflecting face. The effective path length of the penetrant beam in the sample is substantially increased by generating the cyclic tracks whence the number of reflections per unit reflective face area is multiplied.
Optical apparatus as claimed in claim 1 wherein the prism has the shape of a cylinder with a segment removed therefrom to form a lateral concave face, the beam being focusable and locatable on said first concave face so as to emerge therefrom after multiple-reflection.
Claim 2
Dependent Claim
32 words
Optical apparatus as claimed in claim 1 wherein the prism is a hexagonal prism the lateral faces of the prism being relatively disposed such that the internally reflecting angles formed are 45*.
Claim 3
Dependent Claim
98 words
Optical apparatus as claimed in claim 3 wherein the hexagonal prism has one pair of parallel faces coplanar with one pair of sides of a notional square and another pair of parallel faces spaced closer together than are the other pair of sides of the notional square, and two further faces each disposed at substantially 45* to a common face of said one pair of faces and at substantially 45* to each of said other pair of faces, said focusing means being arranged respectively to focus a beam onto, and emerging from, each of said two further faces.
Claim 4
Dependent Claim
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Optical apparatus as claimed in claim 1 wherein the prism is a hexagonal prism the lateral faces of the prism being relatively disposed such that the internally reflecting angles formed are 30* and 60*.
Claim 5
Dependent Claim
112 words
Optical apparatus as claimed in claim 5 wherein the hexagonal prism has one pair of parallel faces coplanar with the shorter pair of sides of a notional rectangle whose adjacent sides have lengths substantially in the ratio sin 30: sin 60 and another pair of parallel faces spaced closer together than are the longer pair of sides of the notional rectangle, and two further faces each disposed at substantially 60* to a common face of said other pair of faces and at substantially 30* to each of said one pair of faces, said focusing means being arranged respectively to focus a beam onto, and emerging from, each of said two further faces.
Claim 6
Dependent Claim
66 words
Optical apparatus as claimed in claim 1 wherein the prism has the shape of a cylinder having a first and second segment removed therefrom to form first and second lateral plane faces, the beam being focusable to be incident on the first face and to emerge through the second face, the first and second faces being relatively disposed to form internally reflecting angles Of < 30*.
Claim 7
Dependent Claim
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Optical apparatus as claimed in claim 7 wherein the first lateral face is concave.
Claim 8
Dependent Claim
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Optical apparatus as claimed in claim 1 wherein the prism has the shape of a cylinder with first and second segments removed therefrom to form first and second lateral concave faces, the faces being substantially diametrically opposite, the beam being focusable and locatable on said first face so as to emerge through the second face.