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CROSS-REFERENCE TO RELATED, COPENDING APPLICATION
Related, copending applications of particular interest to the instant
application are U.S. Ser. No. 011,329 filed Feb. 5, 1987 and U.S. Ser. No.
011,511 filed Feb. 6, 1987 both assigned to the same assignee of the
instant application.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Raman microprobe apparatus for
determining crystal orientation by utilizing polarization selective Raman
microprobe spectroscopy, and more particularly to improvements in
simplicity and accuracy of the apparatus.
2. Description of the Prior Art
Raman microprobe determination of cyrstal orientation is described, e.g.,
in J. Appl. Phys., Vol. 59, 1986, pp. 1103-1110 by J. B. Hopkins et al.
Referring to FIG. 1, there is schematically illustrated an arrangement of a
principal portion in a conventional Raman microprobe apparatus for
determining crystal orientation. An incident beam 1a of circularly
polarized light is converted into a linearly polarized light beam 16 by a
polarizer 7 which can be rotated. The linearly polarized light beam 1b is
deflected by a half mirror 5 and then a light beam 1c thus deflected is
focused on a specimen 4 by an object lens system 3.
Raman light scattered from the specimen 4 is collected as a Raman light
beam 2a by the object lens system 3, a half of which is transmitted as a
beam 2b through the half mirror 5 and then deflected as a beam 2c toward a
polarization analyzer 8 by a complete mirror 6. A Raman light beam 2d
having a particular polarization plane is selected from the beam 2c by the
polarization analyzer 8.
The polarization-selected Raman light beam 2d is then introduced into a
spectrometer (not shown) and then the Raman band of the specimen 4 is
measured. In the conventional apparatus, the polarization intensity
characteristic of the selected Raman light 2d is measured with either the
polarizer 7 or polarization analyzer 8 being fixed and the other being
rotated by degrees. The measured data of the polarization intensity
characteristic are processed by a computer and compared with data derived
theoretically as to known crystal orientation, whereby the crystal
orientation of the specimen 4 can be determined.
In the conventional apparatus, however, it is difficult to make correction
for a measured data which contains experimental errors due to polarization
plane shifts and light intensity distribution changes at the half mirror 5
and complete mirror 6.
In FIG. 1, linearly polarized light 1b having a particular polarization
angle is selected by the polarization 7 from circularly polarized incident
light 1a. This linearly polarized light 1b is reflected by the half mirror
5 and then slightly changes to linearly polarized light 1c having a
polarization angle and intensity distribution both shifted a little from
those of the light 1b. As well known, the reason is that the reflectance
of a mirror changes depending on the polarization angle of light. Since
the Raman scattering is excited by the polarized light 1c slightly
different from the polarized light 1b, it is necessary to make correction
as to an error in the measured data which is caused by the difference
between the light 1b and the light 1c.
When Raman light 2a is transmitted through the half mirror 5, it also
changes to light 2b having slightly different polarization components and
slightly different intensity distribution. Further, when the light 2b is
reflected by the complete mirror 6, it slightly changes to light 2c. A
polarization angle and intensity distribution of linearly polarized light
2d selected from the light 2c are slightly different from those of the
Raman light just as scattered from the specimen 4. Therefore, it is also
necessary to make correction as to errors in the measured data which is
caused by the polarization angle shifts and intensity distribution changes
in the Raman light at the half mirror 5 and the complete mirror 6.
As described above, it is necessary in the conventional apparatus to make
correction for the measured data as to the polarization shifts in both the
incident light and Raman light. However, since it is difficult to separate
the errors in the obtained data due to the respective polarization shifts
in the incident light and the Raman light, it is compelled to make
averaged correction. Therefore, some error still remains in the corrected
data, and the accurate value can not be known.
Further, since the measurements are carried out with either the polarizer 7
or polarization analyzer 8 being rotated and the other being fixed in the
conventional apparatus, not only the two optical parts of the polarizer
and analyzer but also a parameter representing the analyzer relation
between the polarizer and analyzer is indispensable.
SUMMARY OF THE INVENTION
In view of the prior art, it is an object of the present invention to
provide a Raman microprobe apparatus for determining crystal orientation,
in which it is not needed in the measured data to take into consideration
the polarization shifts at the half mirror and complete mirror.
It is another object of the present invention to provided a Raman
microprobe apparatus for determining crystal orientation, in which not
only the number of optical parts but also the number of parameters in
analyzing data is decreased by providing a polarizer which functions not
only as the prior art polarizer but also as the prior art analyzer.
According to the present invention, a Raman microprobe apparatus for
determining crystal orientation comprises a half mirror for deflecting
circularly polarized incident light toward a specimen, a polarizer for
selecting linearly polarized incident light from the deflected incident
light, and an object lens system for focusing the linearly polarized
incident light onto the specimen, wherein Raman light scattered from the
specimen is collected as a Raman light beam by the object lens system and
linearly polarized by the polarizer before it is transmitted through the
half mirror.
Namely, the circularly polarized incident light is converted by the
polarizer into the linearly polarized incident light after deflected by
the half mirror and just before focused on the specimen by the object lens
system. Therefore, there is no shift between the intended polarization
angle and practical polarization angle in the incident light focused on
the specimen.
Meanwhile, just after the scattered Raman light is collected by the object
lens system and before the collected Raman light is transmitted through
the half mirror, linearly polarized Raman light having the intended
polarization angle is selected by the polarizer from the collected Raman
light. Therefore, the practically measured Raman light corresponds
directly to that having the intended polarization angle.
Further, since the polarization polarizes not only the incident light but
also the Raman light, the linearly polarized Raman light to be measured
has the completely same polarization angle as that of the linearly
polarized incident light. In other words, there is not needed a parameter
representing the polarization angular relation between the linearly
polarized incident light and linearly polarized Raman light.
These objects and other objects, features, aspects and advantages of the
present invention will become more apparent from the following detailed
description of the present invention when taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram illustrating an optical system in a principal
portion of a conventional Raman microprobe apparatus for determining
crystal orientation; and
FIG. 2 is a schematic diagram illustrating an optical system in a principal
portion of a Raman microprobe apparatus for determining crystal
orientation according to an embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 2, when circularly polarized incident light 1a is
deflected by a half mirror 5, it changes to a little elliptically
polarized incident light 1d. Linearly polarized light 1e having a
particular polarization plane is selected from the light 1d by a polarizer
9 and then focused on a specimen by an object lens system 3. Raman light
scattered from the specimen 4 is collected as a Raman light beam 2a by the
object lens system 3. Linearly polarized Raman light 2e having the same
polarization plane as that of the incident light 1e is selected from the
Raman light 2a by the polarizer 9. When the linearly polarized Raman light
2e is transmitted through the half mirror 5, it changes to light 2f having
a slightly changed polarization direction and slightly changed intensity
distribution. Similarly, when the Raman light 2f is deflected by the
complete mirror 6, it changes to light 2g having a further slightly
changed polarization direction and further slightly changed intensity
distribution. Then, the linearly polarized Raman light 2g is introduced
into a spectrometer (not shown). In the spectrometer, the Raman bands of
the specimen 4 are separated and the light intensity is measured with
respect to various polarization planes. The measured data of the
polarization characteristic in the Raman light is compared with that
derived theoretically as to known crystal orientation, whereby the crystal
orientation of the specimen 4 can be determined.
In the apparatus of FIG. 2, as described above, the polarization angle of
the incident light is selected just before the incident light is focused
on the specimen and then the polarization angle of the Raman light is
selected just after the Raman light is collected from the specimen.
Therefore, it is not necessary to take into consideration the shifts of
the polarization angle at the half mirror 5 and complete mirror 6, and it
is necessary only to make correction as to the measured light intensity.
In this case, once data for the intensity correction are prepared, they do
not change during the measurements. Therefore, the light intensity can be
measured, precisely corresponding to the polarization angle in the
incident light and the Raman light.
Further, since the polarizer 9 in FIG. 2 functions not only as the prior
art polarizer 7 for the incident light but also as the prior art analyzer
8 for the Raman light, the number of the optical parts is decreased by
one. Accordingly, although the parameter representing the angular relation
between the polarizer 7 and analyzer 8 is necessary in analyzing the data
measured with the conventional apparatus of FIG. 1, such a parameter is
not necessary with the apparatus of FIG. 2.
Although the polarizer 9 was provided between the half mirror 5 and the
object lens system 3 in the above described embodiment, it may be provided
in the object lens system 3 or between the object lens system 3 and
specimen 4. In this case, however, the performance of the polarizer is
reduced a little, because convergent incident light and divergent Raman
light are introduced into the polarizer.
Although the present invention has been described and illustrated in
detail, it is clearly understood that the same is by way of illustration
and example only and is not to be taken by way of limitation, the spirit
and scope of the present invention being limited only by the terms of the
appended claims.
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