Optics: measuring and testing – By polarized light examination – Of surface reflection
Reexamination Certificate
2000-11-13
2001-05-29
Kim, Robert H. (Department: 2877)
Optics: measuring and testing
By polarized light examination
Of surface reflection
Reexamination Certificate
active
06239873
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a device for measurement of polarized light. More specifically, the present invention relates to devices for simultaneous measurement of two orthogonal polarization states of scattered light.
2. Description of the Related Art
Scattering systems normally project polarized light from a single source toward a sample and measure at least a portion of the light which scatters off the sample at different scattering angles to provide information about the sample.
The simultaneous measurement of two orthogonal polarization states of scattered light from a sample is often desired to compare the intensities of the two polarized states as a means to identify characteristics of the sample. However, to accomplish this, a complicated system is required, which includes a series of modulators, such as electro-optic crystals, and control means to operate the modulators.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to overcome the problems of the prior art.
To this end, according to the present invention, there is provided an apparatus for simultaneous measurement of two polarization states of scattered light, the apparatus comprising:
(a) an illumination unit comprising:
a first laser unit for providing a first beam of polarized light having a first wavelength &lgr;
1
and a first state of polarization;
a second laser unit for providing a second beam of polarized light having a second wavelength &lgr;
2
, which is different from the first wavelength, and a second state of polarization; which is different from the first state of polarization;
a first polarization beamsplitter positioned for receiving the first and second light beams, so that the first and second light beams are coincident with each other after exiting the first beamsplitter, the first beamsplitter for passing the first light beam and reflecting the second light beam;
an aperture unit for providing a passage of the first and second light beams after exiting the first beamsplitter to illuminate a sample; and
(b) a measuring unit comprising:
a second polarization beamsplitter positioned for receiving at least a portion of the first light beam and a portion of the second light beam after illuminating the sample, the second beamsplitter for passing the portion of the first light beam and reflecting the portion of the second light beam;
a first notch filter positioned for receiving the portion of the first light beam which has exited the second beamsplitter, the first notch filter for filtering the portion of the first light beam except for a range of wavelengths which includes the first wavelength of the first beam and which does not include the second wavelength of the second beam; and
a second notch filter positioned for receiving the portion of the second light beam which has been reflected by the second beamsplitter, the second notch filter for filtering the portion of the second light beam except for a range of wavelengths which includes the second wavelength of the second beam and which does not include the first wavelength of the first beam.
The illumination may further include a first spatial filter unit for collimating the first beam provided by the first laser unit, the first spatial filter unit being positioned in an optical path between the first laser unit and the first beamsplitter; and
a second spatial filter unit for collimating the second beam provided by the second laser unit, the second spatial filter unit being positioned in an optical path between the second laser unit and the first beamsplitter.
The measuring unit may further include:
a third spatial filter unit for collimating the portion of the first beam and the portion of the second beam after illuminating the sample, the third spatial filter unit being positioned in an optical path between the sample and the second beamsplitter.
According to an aspect of the invention, a length of both of the first wavelength &lgr;
1
and the second wavelength &lgr;
2
may satisfy the following equation:
|&lgr;
1
−&lgr;
2
|<<&lgr;
1
.
In addition, the first laser unit and the second laser unit comprise diode lasers.
The first laser unit and the second laser unit may comprise diode lasers.
The first state of polarization of the first beam of light is s-polarization, and the second state of polarization of the second beam of light is p-polarization.
In addition, the first notch filter and the second notch filter provide a respective output of light to a measuring unit for measuring an intensity of the respective outputs.
According to another embodiment of the present invention, an apparatus for simultaneous measurement of two polarization states of scattered light, the apparatus comprising:
(a) an illumination unit comprising:
a first laser unit for providing a first beam of polarized light having a first wavelength &lgr;
1
and a first state of polarization;
a second laser unit for providing a second beam of polarized light having a second wavelength &lgr;
2
, which is different from the first wavelength, and a second state of polarization, which is different from the first state of polarization;
a first polarization-preserving beamsplitter positioned to receive the first and second light beams so that the first and second light beams are coincident with each other after exiting the first beamsplitter, the first beamsplitter for passing the first light beam and reflecting the second light beam;
an aperture unit for providing a passage of the first and second light beams after exiting the first beamsplitter to illuminate a sample; and
(b) a measuring unit comprising:
a second polarization-preserving beamsplitter positioned for receiving at least a portion of the first light beam and a portion of the second light beam after illuminating the sample, the second beamsplitter for passing the portion of the first light beam and reflecting the portion of the second light beam;
a first notch filter positioned for receiving the portion of the first light beam having the first polarized state, which has been passed by the second beamsplitter, the first notch filter for filtering the portion of the first light beam except for a range of wavelengths which includes the first wavelength of the first beam and which does not include the second wavelength of the second beam; and
a second notch filter positioned for receiving the portion of the second light beam having the second polarized state, which has been reflected by the second beamsplitter, the second notch filter for filtering the portion of the second light beam except for a range of wavelengths which includes the second wavelength of the second beam and which does not include the first wavelength of the first beam.
The illumination unit may further include:
a first spatial filter unit for collimating the first beam provided by the first laser unit, the first spatial filter unit being positioned in an optical path between the first laser unit and the first beamsplitter;
a second spatial filter unit for collimating the second beam provided by the second laser unit, the second spatial filter unit being positioned in an optical path between the second laser unit and the first beamsplitter;
a first polarizer positioned between the first spatial filter unit and the first beamsplitter; and
a second polarizer positioned between the second spatial filter unit and the first beamsplitter.
The measuring unit may further include:
a third spatial filter unit for collimating the portion of the first beam and the portion of the second beam after illuminating the sample, the third spatial filter unit being positioned in an optical path between the sample and the second beamsplitter;
a third polarizer positioned between the first notch filter and the second polarization-preserving beamsplitter; and
a fourth polarizer positioned between the second notch filter and the second polarization-preserving beamsplitter.
In addition, the apparatus may include a rotation unit for rotating at least one of
Clohan, Jr. Paul S.
Kim Robert H.
Stafira Michael P.
The United States of America as represented by the Secretary of
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