title: Thermal diffusivity imaging with the thermal lens microscope.
abstract: A coaxial thermal lens microscope was used to generate images based on both the absorbance and thermal diffusivity of histological samples. A pump beam was modulated at frequencies ranging from 50 kHz to 5 MHz using an acousto-optic modulator. The pump and a CW probe beam were combined with a dichroic mirror, directed into an inverted microscope, and focused onto the specimen. The change in the transmitted probe beam's center intensity was detected with a photodiode. The photodiode's signal and a reference signal from the modulator were sent to a high-speed lock-in amplifier. The in-phase and quadrature signals were recorded as a sample was translated through the focused beams and used to generate images based on the amplitude and phase of the lock-in amplifier's signal. The amplitude is related to the absorbance and the phase is related to the thermal diffusivity of the sample. Thin sections of stained liver and bone tissues were imaged; the contrast and signal-to-noise ratio of the phase image was highest at frequencies from 0.1-1 MHz and dropped at higher frequencies. The spatial resolution was 2.5 μm for both amplitude and phase images, limited by the pump beam spot size.
authors.affiliation: Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA.
authors.forename: Oluwatosin O
authors.initials: OO
authors.lastname: Dada
authors.forename: Peter E
authors.initials: PE
authors.lastname: Feist
authors.forename: Norman J
authors.initials: NJ
authors.lastname: Dovichi
mesh_terms: D000465:Algorithms; D001842:Bone and Bones / Q000648:ultrastructure; D004867:Equipment Design; D007834:Lasers; D007909:Lenses; D008099:Liver / Q000648:ultrastructure; D008853:Microscopy / Q000295:instrumentation* / Q000379:methods*; D059629:Signal-To-Noise Ratio; D013696:Temperature