Scanning microscope with enhanced fov and na

A scanning microscope apparatus for acquiring an image of a sample, comprising:

• a) a source of laser light energizable to generate a beam having a beam width and an excitation wavelength range;
• b) a beam expander configured to enlarge the beam width of the laser light and to direct a collimated beam along a beam path;
• c) a scanner in the beam path and energizable to scan the beam in a raster pattern, wherein the scanner comprises:
• (i) a first scanning element for scanning with respect to a first scan axis;
• and
• (ii) a second scanning element for scanning with respect to a second scan axis that is perpendicular to the first scan axis;
• d) an afocal relay disposed to optically co-locate the first scanning element that scans along the first axis and the second scanning element that scans along an orthogonal axis.
• e) a catadioptric objective that is disposed to receive the scanned beam, wherein the catadioptric objective comprises
• (i) a curved partially transmissive mirror surface symmetric about an optical axis and disposed to focus a portion of the received scanned collimated beam toward a focal plane at the sample,
• wherein the mirror surface has a center of curvature either at an axis of rotation of the scanner or at an image of the axis of rotation of the scanner;
• (ii) a reflective polarizer that is disposed in the path of both collimated light of a first polarization state and focused light of an orthogonal polarization state, wherein the reflective polarizer is configured to cooperate with the curved mirror surface to direct the focused light toward the sample;
• (iii) one or more polarization retarders disposed along the optical axis to condition excitation light that is conveyed toward and away from the curved mirror surface;
• and
• f) a first beam splitter configured to separate the generated laser light from a signal that is excited from the sample and to direct the excited signal toward a detector.

A method for scanning a sample to acquire an image, the method comprising:

• a) energizing a source of laser light to generate a beam having a beam width and an excitation wavelength range;
• b) enlarging the beam width of the laser light and directing a collimated beam along a beam path;
• c) scanning the collimated beam in a raster pattern;
• d) disposing a catadioptric objective to receive the scanned beam, wherein the catadioptric objective comprises:
• (i) a curved partially transmissive mirror surface symmetric about an optical axis and disposed to focus a portion of the received scanned collimated beam toward a focal plane at the sample,
• wherein the mirror surface has a center of curvature either at an axis of rotation of the scanner or at an image of the axis of rotation of the scanner;
• (ii) a reflective polarizer that is disposed in the path of both collimated light of a first polarization state and focused light of an orthogonal polarization state, wherein the reflective polarizer is configured to cooperate with the curved mirror surface to direct the focused light toward the sample;
• (iii) one or more polarization retarders disposed along the optical axis to condition excitation light that is conveyed toward and away from the curved mirror surface;
• e) separating the generated laser light from a signal that is excited from the sample;
• and
• f) forming the image from the sample light.