Immersion lens assemblies for use in optical coherence tomography systems
An optical coherence tomography (OCT) measurement system for precision measurement of a translucent sample is provided. The system includes an optical coherence tomography (OCT) imaging system comprising a broadband light source, a reference path with reference path length, and sample path with a beam scanning assembly and an imaging lens assembly; a sample positioning assembly including an immersion bath for positioning the translucent sample within an immersion bath; a position assembly for locating the translucent sample within a field of view (FOV) of the OCT imaging system; an immersion lens assembly associated with the imaging lens assembly configured to eliminate an air to bath refractive interface between a distal surface of the OCT imaging lens including an immersion tip and a surface of the bath; a first set of calibration parameters that relate a position of a scanning beam at an imaging plane to drive signals of the scanning assembly; and a second set of calibration parameters for relating an optical path length or optical path length variation of the scanning beam at an imaging plane to the position of the scanning beam or to the drive signals of the scanning assembly.
1. A lens assembly for attachment to an optical coherence tomography (OCT) imaging system, wherein the OCT imaging system comprises:
a sample arm that delivers illumination from a broadband OCT light source to a sample positioned proximate an object plane of the imaging system and includes a substantially telecentric focal system that focuses the light from the broadband OCT light source at an object plane substantially perpendicular to an optical axis of the focal system,
wherein the substantially telecentric focal system includes a transmissive optical wedge positioned within an optical path between a focusing lens and the sample;
wherein the optical wedge is substantially transparent across a wavelength range of the broadband optical source;
wherein the optical wedge has a first surface and a second surface, wherein the first surface and the second surface are non-perpendicular to the optical axis of the focal system and non-parallel to the object plane; and
wherein an angle of the first surface of the optical wedge and an angle of the second surface of the optical wedge are designed such that object space telecentricity is maintained when the subject and the object plane are within a medium having a refractive index greater than the refractive index of the medium that Is between the focusing lens and the optical wedge.
2. The assembly of claim 1 :
wherein a ray passing through the optical wedge is laterally shifted, but angularly un-deviated; and
wherein specular reflections from the optical wedge reflect at an angle outside of a numerical aperture of an OCT beam.
3. The assembly of claim 1 , wherein the optical wedge comprises an anti-reflection coating to reduce optical losses at an air-wedge interface and a bath-wedge interface.
4. The assembly of claim 1 , wherein the optical wedge comprises N-BK7 glass with a refractive index of 1.509, a wedge with a first surface angle of two degrees with respect to the optical axis of the focal system and a second surface angle of six degrees with respect to the optical axis of the focal system.