Polarization scrambler and monochromator

Details Polarization scrambler and monochromator Polarization scrambler and monochromator

2001-11-26

2003-11-25

Robinson, Mark A. (Department: 2872)

Optical: systems and elements

Polarization without modulation

Polarization using a time invariant electric, magnetic, or...

Reexamination Certificate

active

06654167

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a polarization scrambler used for eliminating polarization dependence of a monochromator and a monochromator using the polarization scrambler.
2. Description of the Related Art
Generally, a monochromator has polarization dependence and when light such as linearly polarized light biased in a particular direction launches, output characteristics different depending on a polarization direction are shown even in the light with the same energy. In order to eliminate such polarization dependence, the polarization dependence must be eliminated using a polarization scrambler for converting the incident light having any polarization state into circularly polarized light or non-polarized light.
First, the polarization dependence of the monochromator will be described using a configuration of a conventional monochromator shown in FIG.
12
.
A diffraction grating is used in the monochromator. Then, the diffraction grating has a property in which diffraction efficiency depends on a polarization state of incident light. That is, a polarization component vertical to grooves carved on the diffraction grating is different from a polarization component horizontal to the grooves in reflectance. Because of this, in the monochromator using the diffraction grating, the efficiency depends on the polarization state of the incident light and a trouble has been caused in the case of measuring spectral characteristics of the light. As means for solving this problem, a polarization scrambler having a function of converting the incident light into light with a state in which many polarization states are mixed in order to eliminate the polarization dependence of the light incident to the diffraction grating has been used.
Then, in the conventional monochromator, birefringent elements such as quartz or calcite have been used as a polarization scrambler
7
.
In
FIG. 12
, numeral
4
is an incident slit to which light is launched, and numeral
7
is a polarization scrambler, and numeral
6
is a diffraction grating, and numeral
9
is an emission slit, and numeral
5
is a first concave mirror for guiding the light passing through the polarization scrambler
7
to the diffraction grating
6
, and numeral
8
is a second concave mirror for guiding the light from the diffraction grating
6
to the emission slit
9
.
The polarization scrambler
7
is placed in the back of the incident slit
4
so that an optical axis becomes a direction of 45° with respect to a groove direction of the diffraction grating
6
.
Next, an example of a polarization scrambler according to a conventional art will be described using FIG.
7
.
In
FIG. 7
, arrow
71
is an optical axis of a quartz plate
7
A and arrow
72
is an optical axis of a quartz plate
7
B. The quartz plate
7
A has the same shape as that of the quartz plate
7
B, and the quartz plate
7
A and the quartz plate
7
B are bonded together with the optical axis
71
and the optical axis
72
intersecting each other to construct the polarization scrambler
7
.
In the quartz plate
7
A, the thickness changes continuously along a direction parallel to the optical axis
71
of the quartz plate
7
A (in the drawing, the thickness becomes thick in the bottom parallel to the optical axis
71
and becomes thin in the top), and also in the quartz plate
7
B, the thickness changes continuously along a direction vertical to the optical axis
72
of the quartz plate
7
B (in the drawing, the thickness becomes thick in the top vertical to the optical axis
72
and becomes thin in the bottom).
Next, a function of the polarization scrambler
7
of
FIG. 7
will be described by means of FIG.
8
.
FIG. 8
is a side view of the polarization scrambler
7
.
Quartz constructing the polarization scrambler
7
has an optical axis in a particular direction because of its crystal structure, and has a property of providing a phase difference between a light component of oscillating in parallel to the optical axis and a component of oscillating in vertical to the optical axis of light passing through the quartz.
The phase difference provided here is proportional to a thickness of the quartz. Therefore, since the quartz plate
7
A or the quartz plate
7
B changes continuously in thickness, the thickness of the quartz differs by places through which the light passes, so that the phase difference provided by the places in which the light passes through the quartz plate differs.
For example, even in case that polarization states before transmission of the light of signs G, H, I of
FIG. 8
are same, the phase differences provided by the quartz plate
7
A and the quartz plate
7
B differ respectively, so that the polarization states of the light after transmission differ respectively (in the quartz plate
7
A, a phase of the light of sign I lags behind a phase of the light of sign G and in the quartz plate
7
B, a phase of the light of sign G lags behind a phase of the light of sign I).
Therefore, the polarization scrambler
7
can convert the polarization states of the light into a state in which many polarization states are mixed spatially. That is, the polarization states are disturbed spatially.
Incidentally, the polarization scrambler
7
does not have an effect with respect to light components parallel or vertical to the optical axis and these light components are transmitted as it is.
Next, an operation of a monochromator using the polarization scrambler
7
made of the two quartz plates will be described by means of FIG.
12
.
In the polarization scrambler
7
, incident light passing through the incident slit
4
is converted into a state in which many polarization states are mixed.
Light components parallel or vertical to the optical axis are transmitted as it is, but these components launch at an angle of 45° with respect to grooves of the diffraction grating
6
.
Therefore, even in case that the polarization state of the incident light is any state, a ratio between a component vertical to the grooves and a component parallel to the grooves always becomes equal in the incident light to the diffraction grating
6
. Hence, efficiency does not vary depending on the polarization state of the incident light, so that a monochromator without polarization dependence can be achieved.
Next, problems of a conventional art will be described by FIG.
11
.
FIG. 11
is a side view of the polarization scrambler
7
made of the two quartz plates shown in FIG.
7
.
Since mutual optical axes of the quartz plate
7
A and the quartz plate
7
B intersect at right angles, light parallel to the optical axis of the quartz plate
7
A becomes light vertical to the optical axis of the quartz plate
7
B and light vertical to the optical axis of the quartz plate
7
A becomes light parallel of the optical axis of the quartz plate
7
B. Therefore, refractive indexes differ in both sides of a slope in which the two quartz plates are bonded together, so that incident light causes refraction in the slope.
Further, a light component parallel to the optical axis
71
of the quartz plate
7
A differs from a light component vertical to the optical axis
71
in an angle of refraction in the slope. For example, in incident light N of
FIG. 11
, a component parallel to the optical axis
71
becomes refracted light O and a component vertical to the optical axis
71
becomes refracted light P.
In this manner, the light is split into two portions along a direction of the slope of the polarization scrambler
7
.
Therefore, also in the monochromator as shown in
FIG. 12
using the polarization scrambler
7
, the light is split in two directions by the polarization scrambler
7
and also a position in which the light is focused on the emission slit
9
is split into two portions.
FIG. 9
is a front view of the emission slit
9
in FIG.
12
.
A black dot K of
FIG. 9
is a focal position of the case that the polarization scrambler
7
is absent.
Also, black dots J and L are two focal positions of the case that incident light is split in the slope of the po

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