|A detection method for a measurement of a microscopic
object is required in order to detect specified objects contained
in a channel of a chip. IMT provide Thermal Lens Microscope developed
by KAST Kitamori Project jointly with Kitamori laboratory of the
University of Tokyo for a detection tool of the microchip chemistry.
A principle of the Thermal Lens Microscope is shown as follows.
If there is a material absorbs both an excitation laser and a probe
laser through an objective lens, the light energy except the energy
absorbed by the sample is all released to the solvent as thermal
energy, and the phenomenon produces the increase in temperature.
According to the spatial distribution of temperature, a high
gradient of the temperature distribution is formed around the
optic axis of the laser by the intensity distribution and the
thermal diffusion of the laser. In the case of fluid such as water,
lower refractive index at the center of the optic axis and higher
refractive index at the banlieue of the optic axis are formed
because the refractive index is lowered by the temperature rise.
The refractive index distribution is equivalent to the concave
lens and it is so called thermal lens. Sensitivity of the thermal
lens is proportional to the calorific value generated; that is
to say it is proportional to the amount and the concentration
of a sample, therefore, the quantity of a sample can be determined
by measuring the sensitivity of the thermal lens. For an actual
measurement, excitation laser is modulated, and intensity change
of the probe laser is simultaneously detected.