Real-time focusing in line scan imaging

A system for scanning a sample to acquire a digital image of the sample, the system comprising:

• a stage configured to support a sample;
• an objective lens having a single optical axis that is orthogonal to the stage;
• an imaging sensor;
• a focusing sensor, wherein one point on the focusing sensor is parfocal with the imaging sensor;
• at least one first beam splitter optically coupled to the objective lens and configured to receive a field of view corresponding to the optical axis of the objective lens, and simultaneously provide at least a first portion of the field of view to the imaging sensor and at least a second portion of the field of view to the focusing sensor, wherein the first portion of the field of view is a first region of the field of view, and wherein the second portion of the field of view is a second region of the field of view that is offset from the first region of the field of view;
• and
• focusing optics,
• wherein the focusing sensor comprises a first region and a second region, wherein the first region receives the second portion of the field of view along a first optical path, wherein the second region receives a mirrored second portion of the field of view along a second optical path, wherein the focusing sensor is tilted at an angle with respect to each of the first optical path and the second optical path, wherein at least one point on both the first region of the focusing sensor and the second region of the focusing sensor is parfocal with the imaging sensor, wherein the second portion of the field of view is received by the first region of the focusing sensor at a focal distance, and the mirrored second portion of the field of view is received by the second region of the focusing sensor at the same focal distance, wherein the first region of the focusing sensor acquires a first image of the second portion of the field of view, wherein the second region of the focusing sensor acquires a second image of the mirrored second portion of the field of view, wherein the first image comprises pixels acquired at decreasing focal distances in a direction from a first side of the first image to a second side of the first image, and wherein the second image comprises pixels acquired at decreasing focal distances in a same direction as the first image, and
• wherein the focusing optics comprise at least one second beam splitter that is optically coupled to the at least one first beam splitter and splits a beam, conveying the second portion of the field of view into the first optical path and the second optical path, wherein the focusing optics further comprise at least one mirror that reflects the split beam in one of the first optical path and the second optical path, wherein the focusing optics further comprise a dove prism in the second optical path, between the at least one first beam splitter and the second region of the focusing sensor, that flips the second portion of the field of view to form the mirrored second portion of the field of view, wherein the at least one mirror comprises a first mirror and a second mirror, and wherein the second optical path comprises a reflection from the first mirror onto the second mirror, a reflection from the second mirror back to the at least one second beam splitter, and a path from the at least one second beam splitter to the second region of the focusing sensor, such that the second portion of the field of view is flipped to form the mirrored second portion of the field of view.