A method and device for photothermal imaging tiny metal particles which are
immersed in a given medium like a living cell deposited onto a transparent
glass slide. The given medium and immersed tiny metal particles are
illuminated through separate phase reference laser beam and sensitive
probe laser beam, with the sensitive probe laser beam including a heating
laser beam undergoing through impingement on the given medium slight phase
changes induced by photothermal effect due to a local heating, in the
absence of any substantial phase changes to the phase reference laser
beam. Illuminating is performed by focusing the separate phase reference
and sensitive probe laser beam through the transparent glass slide at a
given depth within the given medium and a transmitted phase reference
laser beam and a transmitted sensitive probe laser beam undergoing the
slight phase changes are generated. An image of the given medium at the
given depth is formed through the transmitted phase reference and
sensitive probe laser beam and the slight phase changes on the transmitted
sensitive probe laser beam with reference to the reference phase laser
beam are detected so as to allow each of the tiny metal particles to be
imaged as an optical label.
