Abstract

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.

© 2008 Optical Society of America

Graded-field autoconfocal microscopy

Kengyeh K. Chu, Ran Yi, and Jerome Mertz
Opt. Express 15(5) 2476-2489 (2007)

Autoconfocal transmission microscopy based on two-photon-induced photocurrent of Si photodiodes

Chulmin Joo, Chun Zhan, Qing Li, and Siavash Yazdanfar
Opt. Lett. 35(1) 67-69 (2010)

Autoconfocal microscopy with nonlinear transmitted light detection

Thomas Pons and Jerome Mertz
J. Opt. Soc. Am. B 21(8) 1486-1493 (2004)

Transmission confocal laser scanning microscopy with a virtual pinhole based on nonlinear detection

C. Yang and J. Mertz
Opt. Lett. 28(4) 224-226 (2003)

Single-photon-counting detector for increased sensitivity in two-photon laser scanning microscopy

Richard K. P. Benninger, William J. Ashby, Elisabeth A. Ring, and David W. Piston
Opt. Lett. 33(24) 2895-2897 (2008)