Autoconfocal microscopy with a cw laser and thermionic detection.
We introduce an application of thermionic emission in a PMT photocathode. Because of the nonlinear dependence of thermionic emission on absorbed laser power, a conventional PMT is found to produce a virtual pinhole effect that rejects unfocused light at least as strongly as a physical pinhole. This virtual pinhole effect is exploited in a scanning transmission confocal microscope equipped with a cw laser source. Because the area of the PMT photocathode is large, signal descanning is not required and thermionic detection acts as a self-aligned pinhole. Our technique of thermionic-detection autoconfocal microscopy is further implemented with graded-field contrast to obtain enhanced phase-gradient sensitivity in unlabeled samples, such as rat hippocampal brain slices.
Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA.
Daryl
D
Lim
Kengyeh K
KK
Chu
Jerome
J
Mertz
D000818:Animals; D006624:Hippocampus / Q000648:ultrastructure; D007834:Lasers; D008853:Microscopy / Q000295:instrumentation / Q000379:methods; D051381:Rats