Jf. Power et Sw. Fu, Longitudinal light profile microscopy: A new method for seeing below the surfaces of thin-film materials, APPL SPECTR, 53(12), 1999, pp. 1507-1519
Longitudinal light profile microscopy (LLPM) is introduced in this work as
a new optical method for depth profiling the properties of thin-him materia
ls. The method uses irradiation of an optically polished cross section of a
prepared thin film sample, by a laser beam propagating along the depth (lo
ngitudinal) axis of the material. An observation microscope, aligned along
an orthogonal axis to the sample cross section, transfers an image of the l
ight profile propagating along the material's longitudinal (depth) axis to
a recording camera. While depth attenuation of the optical beam in the samp
le is dominated by light absorption, and turbid scatter (which our analysis
neglects), light profile images recovered by the microscope use contrast m
echanisms based on luminescence and elastic or inelastic light scatter. Blu
r contributions to the images arising from axial thickness of the light pro
file "object" are shown to be minimal in our microscope. Our experimental s
etup, moreover, is constructed from relatively inexpensive, easily availabl
e components. A number of different image contrast mechanisms, including Lu
minescence and elastic scattering contrast, were demonstrated on materials
with known optical properties, including continuous media and laminates. Th
e sample dimensions and depth-dependent image features were directly observ
able and unambiguous to identify. images recovered on the basis of elastic
scattering showed unusual contrast for optical interfaces in materials whic
h were transparent at the analysis wavelength. The method holds promise for
providing a plethora of new depth-resolved imaging mechanisms.