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Claims  |
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We claim:
1. A super-resolution scanning optical apparatus comprising:
a first coherent light source for emitting a first coherent beam serving as
a primary beam;
a second coherent light source for emitting a second coherent beam which
has either a plane of polarization perpendicular to the plane of
polarization of said first coherent beam or a wavelength different from
the wavelength of said first coherent beam;
a phase plate for receiving said second coherent beam and emitting a
subsidiary beam which has an intensity distribution in which peak values
are placed at least on both sides of the center of the subsidiary beam on
a plane perpendicular to an optical axis and the principal portion of the
subsidiary beam is equal in size to the principal portion of the primary
beam;
a focusing means for superimposing the primary beam emitted from said first
coherent light source and the subsidiary beam emitted from said phase
plate upon each other and focusing, as a minute size light beam, each of
the primary beam and the subsidiary beam onto a plane to be scanned;
a scanning means for scanning said plane to be scanned with a light beam
composed of the primary beam and the subsidiary beam being superimposed
upon each other;
a light separating means for receiving the light beam transmitted or
reflected by said plane to be scanned, separating said light beam into the
primary beam and the subsidiary beam through polarization separation or
wavelength separation, and emitting them;
an optical detecting means for individually detecting the intensity of the
primary beam and the intensity of the subsidiary beam and outputting a
light intensity signal; and
a calculating means for calculating, based on the light intensity signal
outputted from said optical detecting means, a super-resolution scanning
signal and outputting it.
2. A super-resolution scanning optical apparatus according to claim 1,
further comprising:
an output means for displaying, printing, or storing information on an
image on said plane to be scanned; and
a control means for receiving the super-resolution scanning signal
outputted from said calculating means and controlling said output means so
that it displays, prints, or stores the information on the image on said
plane to be scanned.
3. A super-resolution scanning optical apparatus according to claim 1,
wherein
said first and second coherent light sources are a pair of linearly
polarized lasers which are arranged so that their planes of polarization
are perpendicular to each other.
4. A super-resolution scanning optical apparatus according to claim 1,
wherein
said light separating means consists of a substrate the refractive index of
which is uniaxially anisotropic and a polarizing holographic device or a
polarizing diffraction grating so as to serve as a polarization separating
means for separating said light beam into said primary beam and said
subsidiary beam through polarization separation.
5. A super-resolution scanning optical apparatus according to claim 1,
wherein
said light separating means is composed of a multi-layer dielectric filter
so as to serve as a wavelength separating means for separating said light
beam into said primary beam and said subsidiary beam through wavelength
separation.
6. A super-resolution scanning optical apparatus according to claim 1,
wherein
said phase plate is divided into N (N is an integer equal to or more than
2) regions around the center thereof, said N regions providing a relative
phase difference advancing stepwise in the sequence of 0, 2.pi./N,
(2.pi./N).times.2, (2.pi./N).times.3, . . . , and (2.pi./N).(N-1) to the
second coherent beam emitted from said second coherent light source and
emits the second coherent beam passing through said N regions as said
subsidiary beam.
7. A super-resolution scanning optical apparatus according to claim 1,
wherein
said scanning means has a pair of acoust-optical deflectors for deflecting
said primary beam and said subsidiary beam in two directions perpendicular
to each other on the plane to be scanned.
8. A super-resolution scanning optical apparatus, comprising:
a coherent light source for emitting a coherent beam;
a polarizing phase plate for receiving the coherent beam emitted from the
coherent light source, separating the coherent beam into a primary beam
and a subsidiary beam which has a plane of polarization perpendicular to
the plane of polarization of the primary beam and an intensity
distribution in which peak values are placed at least on both sides of the
center of said primary beam and the principal portion of the subsidiary
beam is equal in size to the principal portion of said primary beam, and
transmitting the primary beam and the subsidiary beam;
a focusing means for superimposing the primary beam and the subsidiary beam
transmitted through said polarizing phase plate upon each other and
focusing, as a minute size light beam, each of the primary beam and the
subsidiary beam onto a plane to be scanned;
a scanning means for scanning said plane to be scanned with a light beam
composed of the primary beam and the subsidiary beam being superimposed
upon each other;
a light separating means for receiving the light beam transmitted or
reflected by said plane to be scanned, separating said beam into the
primary beam and the subsidiary beam through polarization separation, and
transmitting them;
a photo-detecting means for individually detecting the intensity of the
primary beam and the intensity of the subsidiary beam and outputting a
light intensity signal; and
a calculating means for calculating, based on the light intensity signal
outputted from said photo-detecting means, a super-resolution scanning
signal and outputting it.
9. A super-resolution scanning optical apparatus according to claim 8,
further comprising:
an output means for displaying, printing, or storing information in an
image on said plane to be scanned; and
a control means for receiving the super-resolution scanning signal
outputted from said calculating means and controlling said output means so
that it displays, prints, or stores the information on the image on said
plane to be scanned.
10. A super-resolution scanning optical apparatus according to claim 8,
wherein
said light separating means consists of a substrate the refractive index of
which is uniaxially anisotropic and a polarizing holographic device or a
polarizing diffraction grating so as to serve as a polarization separating
means for separating said light beam into said primary beam and said
subsidiary beam through polarization separation.
11. A super-resolution scanning optical apparatus according to claim 8,
wherein
said polarizing phase plate separates the coherent beam emitted from said
coherent light source into an optical component having a plane of
polarization in one direction and an optical component having a plane of
polarization in another direction, said planes of polarization being
perpendicular to each other, emits, as said primary beam, said optical
component having the plane of polarization in one direction, has a first
region which does not provide any relative phase difference to the optical
component having the plane of polarization in said another direction and a
second region which provides a relative phase difference of .pi. to the
optical component having the plane of polarization in said another
direction, and emits, as said subsidiary beam, the optical component
passing through said first and second regions.
12. A super-resolution scanning optical apparatus according to claim 11,
wherein
said first and second regions are formed around the center of said
polarizing phase plate in four regions so that the two first regions
alternate the two second regions.
13. A super-resolution scanning optical apparatus according to claim 8,
wherein
said polarizing phase plate separates the coherent beam emitted from said
coherent light source into an optical component having a plane of
polarization in one direction and an optical component having a plane of
polarization in another direction, said planes of polarization being
perpendicular to each other, emits the optical component having the plane
of polarization In said one direction without providing any relative phase
difference thereto, has N (N is an integer equal to or more than 2)
regions around the center thereof which provides a relative phase
difference advancing in the sequence of 0, 2.pi./N, (2.pi./N).times.2,
(2.pi./N).times.3 . . . , and (2.pi./N).(N-1) to the optical wave
component having the plane of polarization in said another direction, and
transmits, as said subsidiary beam, the optical wave component passing
through said N regions.
14. A super-resolution scanning optical apparatus comprising:
a first coherent light source for emitting a first coherent beam serving as
a primary beam;
a second coherent light source for emitting a second coherent beam which
has either a plane of polarization perpendicular to the plane of
polarization of said first coherent beam or a wavelength different from
the wavelength of said first coherent beam;
a holographic optical element for receiving said second coherent beam and
emitting a subsidiary beam which has an intensity distribution in which
peak values are placed at least on both sides of the subsidiary beam on a
plane perpendicular to an optical axis and the principal portion of the
subsidiary beam is equal in size to the principal portion of primary beam;
a focusing means for superimposing the primary beam emitted from said first
coherent light source and the subsidiary beam transmitted through said
holographic optical element upon each other and focusing, as a minute size
light be each of the primary beam and the subsidiary beam onto a plane to
be scanned;
a scanning means for scanning said plane to be scanned with a light beam
composed of said primary beam and said subsidiary beam being superimposed
upon each other;
a light separating means for receiving the light beam transmitted or
reflected by said plane to be scanned, separating said light beam into the
primary beam and the subsidiary beam through polarization separation or
wavelength separation, and transmitting them;
a photo-detecting means for individually detecting the intensity of the
primary beam and the intensity of the subsidiary beam and outputting a
light intensity signal; and
a calculating means for calculating, based on the light intensity signal
outputted from said optical detecting means, a super-resolution scanning
signal and outputting it.
15. A super-resolution scanning optical apparatus according to claim 14,
further comprising:
an output means for displaying, printing, or storing information on an
image on said plane to be scanned; and
a control means for receiving the super-resolution scanning signal
outputted from said calculating means and controlling said output means so
that it displays, prints, or stores the information on the image on said
plane to be scanned.
16. A super-resolution scanning optical apparatus according to claim 14,
wherein
said first and second coherent light sources are a pair of linearly
polarized lasers which are arranged so that their planes of polarization
are perpendicular to each other.
17. A super-resolution scanning optical apparatus according to claim 14,
wherein
said light separating means consists of a substrate the refractive index of
which is uniaxially anisotropic and a polarizing holographic device or a
polarizing diffraction grating so as to serve as a polarization separating
means for separating said light beam into said primary beam and said
subsidiary beam through polarization separation.
18. A super-resolution scanning optical apparatus according to claim 14,
wherein
said light separating means is composed of a multi-layer dielectric filter
so as to serve as a wavelength separating means for separating said light
beam into said primary beam and said subsidiary beam through wavelength
separation.
19. A super-resolution scanning optical apparatus according to claim 14,
wherein
said scanning means has a pair of acoust optical deflectors for deflecting
said primary beam and said subsidiary beam in two directions perpendicular
to each other on the plane to be scanned. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates to a super-resolution scanning optical
apparatus for optically processing information by scanning an object with
a focused beam. More particularly, it relates to a super-resolution
scanning optical apparatus which is applicable to a laser scanning
microscope, a bar-code scanner, an image scanner, a microdensitometer, an
optical pickup head apparatus for optical disk, and the like.
The super-resolution scanning optical apparatus mentioned above comprises:
a scanning means for scanning a line or plane with a pair of scanning
beams obtained by focusing a pair of coherent beams onto the scanned
plane; and a photoelectric converting means for detecting the intensity of
the respective scanning beams. The above super-resolution scanning optical
apparatus is equipped with various arrangements that have been devised to
obtain an equivalent fine focal spot equal to or smaller than the
diffraction limited.
FIG. 12 is a schematic view showing the structure of a conventional
image-forming optical system using an annular diaphragm, which is
well-known as a super-resolution optical system, as a double-diffraction
optical system. Such a super-resolution optical system using the annular
diaphragm has found application in optical pickup head apparatus, which
are reported in the following documents.
(1) "High Density Optical Recording by Super-Resolution," Y. Yamanaka, Y.
Hirose and K. Kubota, Proc. Int. Symp. on Optical Memory, 1989, Jap. J. of
Appl. Phys., Vol. 28 (1989) supplement 28-3, pp.197-200.
(2) "Optical Head with Annular Phase-Shifting Apodizer," Hideo Ando,
Tsuneshi Yokota and Koki Tanoue, Jap. J. Appl. Phys., Vol. 32 (1993)
pp.5269-5276, pt. 1, NO.11B.
As shown in FIG. 12, a coherent beam emitted from a coherent light source
50 is turned into parallel beams upon passing through a collimator lens (a
first Fourier transform lens) 51. The resulting parallel beams are then
allowed to pass through apertures 52a and 52b (slits in one dimension) of
an annular diaphragm 52 and converged by an objective lens (a second
Fourier transform lens) 53 so as to form an image, thereby providing a
super-resolution spot as the I(X) which is shown as the power spectrum
(transmittance) of the foregoing annular diaphragm 52. The above document
(1) discloses an optical head which forms such a super-resolution spot in
one dimension and uses only the main lobe thereof obtained by means of
knife-edges constituting a slit. The above document (2) discloses a system
which uses a plurality of phase distributions and a specified amplitude
distribution as the annular diaphragm in order to form a super-resolution
in two dimensions, thereby suppressing the side lobes on both sides of the
main lobe shown in FIG. 12. In the system, the conditions for designing
the annular diaphragm are optimized to suppress the side lobes.
However, the system for suppressing the side lobes by means of the annular
diaphragm is not free from a reduction in intensity of the focused beam.
In the case where the peak intensity of the focused beam is reduced to
about 50% to 15%, e.g., if the full width half maxim (FWHM) of the main
lobe is reduced to 85% of the diffraction limited, the intensity of the
side lobe becomes about 74% of the peak intensity of the main lobe.
As described above, if the image of the aperture through which light is
incident upon the objective lens is formed into a slit or an annularity,
there can be achieved super-resolution smaller than the diffraction
limited with the side lobes suppressed to a certain extent. However, since
the mount of light reaching an image forming plane is reduced
significantly, the quantity of light in the main lobe is also reduced
disadvantageously. Moreover, since the aperture for shielding the side
lobes is provided, a higher accuracy is required in adjusting the optical
path, while the reliability of the apparatus is lowered because the
alignment of the scanning optical system is deteriorated with the passage
of time or for other reasons. Furthermore, the FWHM of the beam is reduced
to about 10% to 20% at most.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide
a super-resolution scanning optical apparatus with extremely high
performance wherein a simple optical system preferably prevents a
significant reduction in the quantity of light, and the equivalent beam
width can be reduced to about 50% of that of the diffraction limited.
A first super-resolution scanning optical system is composed of a
super-resolution scanning optical system, wherein a primary beam having a
peak intensity in the center thereof and a subsidiary beam having peak
intensities at least on both sides of the center thereof, both having
equal-sized principal portions, are incoherently superimposed upon each
other for use in scanning a plane to be scanned and the light beam
transmitted or reflected by the plane to be scanned is separated into the
primary beam and subsidiary beam so that the light intensities thereof are
differentially detected.
Specifically, the first super-resolution scanning optical apparatus
comprises: a first coherent light source for emitting a first coherent
beam serving as a primary beam; a second coherent light source for
emitting a second coherent beam which has either a plane of polarization
perpendicular to the plane of polarization of the above first coherent
beam or a wavelength different from the wavelength of the above first
coherent beam; a phase plate for receiving the above second coherent beam
and emitting a subsidiary beam which has an intensity distribution in
which peak values are placed at least on both sides of the center thereof
on a plane perpendicular to an optical axis and the principal portion
thereof is equal in size to the principal portion of the above primary
beam; a focusing means for superimposing the primary beam emitted from the
above first coherent light source and the subsidiary beam emitted from the
above phase plate upon each other and focusing them onto a plane to be
scanned; a scanning means for scanning the above plane to be scanned with
a light beam composed of the above primary beam and the subsidiary beam
being superimposed upon each other; a light separating means for receiving
the light beam transmitted or reflected by the above plane to be scanned,
separating the light beam into the primary beam and the subsidiary beam
through polarization separation or wavelength separation, and transmitting
them; an optical detecting means for individually detecting the intensity
of the primary beam and the intensity of the subsidiary beam and
outputting a light intensity signal; and a calculating means for
calculating, based on the light intensity signal outputted from the
optical detecting means, a super-resolution scanned signal and outputting
it.
According to the first super-resolution scanning optical apparats, the
primary beam has the normal Airy-disc pattern or has a peak intensity on
the optical axis. On the focal plane, the principal portion of the
subsidiary beam has a beam size equal to the FWHM of the primary beam.
Peaks are formed at least on both sides of the center of the subsidiary
beam. 0n the plane to be scanned, the primary beam and the subsidiary beam
are incoherently superimposed upon each other for scanning, so that the
primary beam forms a beam profile having the Airy-disc pattern or having a
peak intensity in the center thereof, while the subsidiary beam forms a
beam profile having a principal portion equal in size to that of the
primary beam and having a double-humped intensity distribution with peak
values placed at least on both sides of the center thereof. The light beam
obtained by superimposing the primary beam and the subsidiary beam upon
each other on the plane to be scanned is transmitted or reflected by the
plane to be scanned and then separated into the primary and the subsidiary
beams again through polarization or wavelength separation, so that the
intensities thereof are detected individually. The detected light
intensities are differentially calculated so that the output signal is
obtained as a difference in intensity distribution between the primary
beam and the subsidiary beam. Therefore, a super-resolution scanned signal
can surely be obtained with ease. Consequently, the resolving power of the
scanning optical system surpasses that of the diffraction limited of the
objective lens in use, thereby equivalently implementing half the beam
width of the diffraction limited. The subsidiary beam having a
double-humped intensity distribution can easily be generated by means of a
stepped phase plate which provides a relative phase difference varying
from 0 to .pi. to the wavelength of the light transmitted thereby. By
irradiating the phase plate with a coherent beam having substantially the
same intensity distribution as the primary beam, substantially the same
intensity distribution as provided in the peripheral portion of the
primary beam can be provided in the peripheral portion of the
double-humped beam. Such waveform shaping for a beam can be performed by
optimizing the diameter of an aperture through which the primary and
subsidiary beams pass.
A second super-resolution scanning optical apparatus is composed of a
super-resolution scanning optical system, wherein the coherent beam
emitted from a single coherent light source is separated by a polarizing
phase plate into a primary beam having a peak intensity in the center
thereof and a subsidiary beam having peak intensities at least on both
sides of the center of the primary beam, both having planes of
polarization perpendicular to each other, so that they are superimposed
upon each other for use in scanning a plane to be scanned and the light
beam transmitted or reflected by the plane to be scanned is separated
through polarization separation so as to differentially detect the
respective light intensities. Specifically, the second super-resolution
scanning optical apparatus comprises: a coherent light source for emitting
a coherent beam; a polarizing phase plate for receiving the coherent beam
emitted from the coherent light source, separating the coherent beam into
a primary beam and a subsidiary beam which has a plane of polarization
perpendicular to the plane of polarization of the primary beam and an
intensity distribution in which peak values are placed at least on both
sides of the center of the above primary beam and the principal portion
thereof is equal in size to the principal portion of the above primary
beam, and emitting the primary beam and the subsidiary beam; a focusing
means for superimposing the primary beam and subsidiary beam emitted from
the polarizing phase plate upon each other and focusing them onto a plane
to be scanned; a scanning means for scanning the above plane to be scanned
with a light beam composed of the above primary beam and subsidiary beam
being superimposed upon each other; a light separating means for receiving
the light beam transmitted or reflected by the above plane to be scanned,
separating the beam into the primary beam and the subsidiary beam through
polarization separation, and transmitting them; an optical detecting means
for individually detecting the intensity of the primary beam and the
intensity of the subsidiary beam and outputting a light intensity signal;
and a calculating means for calculating, based on the light intensity
signal outputted from the photo-detecting means, a super-resolution
scanning signal and outputting it.
According to the second super-resolution scanning optical apparatus, the
primary beam and subsidiary beam having planes of polarization
perpendicular to each other can be obtained from the coherent beam emitted
from the single coherent light source. Moreover, the principal portion of
the primary beam is equal in size to that of the subsidiary beam. The
primary beam has a peak intensity on the optical axis, while the
subsidiary beam has peak intensities at least on both sides of the center
of the primary beam. On the plane to be scanned, the primary beam and
subsidiary beam are incoherently superimposed upon each other for
scanning. After the light beam obtained by superimposing the primary beam
and subsidiary beam upon each other was transmitted or reflected by the
plane to be scanned, it is separated into the primary beam and subsidiary
beam again through polarization separation so that the intensities thereof
are detected individually. The detected light intensities are
differentially calculated so that an output signal is obtained as a
difference in intensity distribution between the primary beam and the
subsidiary beam. Consequently, a super-resolution scanned signal can
surely be obtained with ease.
Since the primary and subsidiary beams emitted from the single coherent
light source are led to the polarizing phase plate and the plane to be
scanned is provided on their conjugate plane, they are used for scanning
with their optical axes completely coincident with each other, so that an
extremely stable and excellent super-resolution scanning optical system
can be implemented by an extremely simple structure.
A third super-resolution scanning optical apparatus is composed of a
super-resolution scanning optical system using a holographic device in
place of the phase plate of the first super-resolution scanning optical
apparatus.
Specifically, the third super-resolution scanning optical apparatus
comprises: a first coherent light source for emitting a first coherent
beam serving as a primary beam; a second coherent light source for
emitting a second coherent beam which has either a plane of polarization
perpendicular to the plane of polarization of the above first coherent
beam or a wavelength different from the wavelength of the above first
coherent beam; a holographic device for receiving the above second
coherent beam and emitting a subsidiary beam which has an intensity
distribution in which peak values are placed at least on both sides
thereof on a plane perpendicular to an optical axis and the principal
portion thereof is equal in size to the principal portion of the above
primary beam; a focusing means for superimposing the primary beam emitted
from the above first coherent light source and the subsidiary beam emitted
from the above holographic device upon each other and focusing them onto a
plane to be scanned; a scanning means for scanning the above plane to be
scanned with a light beam composed of the above primary beam and said
subsidiary beam being superimposed upon each other; a light separating
means for receiving the light beam transmitted or reflected by the above
plane to be scanned, separating the light beam into the primary beam and
the subsidiary beam through polarization separation or wavelength
separation, and transmitting them; an optical detecting means for
individually detecting the intensity of the primary beam and the intensity
of the subsidiary beam and outputting the respective light-intensity
signals; and a calculating means for calculating, based on the light
intensity signals outputted from the optical detecting means, a
super-resolution scanned signal and outputting it.
According to the third super-resolution scanning optical apparatus, the
primary beam has the normal Airy-disc pattern or has a peak intensity on
the optical axis. On the focal plane, the principal portion of the
subsidiary beam reproduced from the holographic device has a beam size
equal to the FWHM of the primary beam. Peak intensities are formed at
least on both sides of the center of the subsidiary beam. On the plane to
be scanned, the primary beam and subsidiary beam are incoherently
superimposed upon each other for scanning. The light beam obtained by
superimposing the primary beam and subsidiary beam upon each other on the
plane to be scanned is transmitted or reflected by the plane to be scanned
and separated into the primary beam and subsidiary beam through
polarization separation so that the intensities thereof are detected
individually. The detected light intensities are differentially calculated
so that an output signal is obtained as a difference in intensity
distribution between the primary beam and the subsidiary beam.
Consequently, a super-resolution scanned signal can surely be obtained
with ease.
Thus, according to the third super-resolution scanning optical apparatus,
the subsidiary beam can be generated by the holographic device functioning
as a phase plate. Even though complicated procedures are required in the
process of fabricating a phase plate, the apparatus needs the provision of
only one phase plate, so that the holographic devices can be manufactured
on an industrial scale. Alternatively, it is also possible to use a
technique of computer-generated holography whereby a phase plate is
designed on a computer without actual need of fabrication, so that
flexibility in designing and fabrication is enhanced.
Preferably, each of the first to third super-resolution scanning optical
apparatus further comprises: an output means for displaying, printing, or
storing information on an image on the plane to be scanned; and a control
means for receiving the super-resolution scanning signal outputted from
the calculating means and controlling the output means so that it
displays, prints, or stores the information on the image on the plane to
be scanned.
Thus, the super-resolution scanned signal outputted from the
super-resolution scanning optical system can be displayed, printed, or
stored so that information on the scanned image can be outputted to a
standard (conventional) CRT display unit, printing unit, or storing unit
(image memory). Consequently, the super-resolution scanning optical system
can be used as a super-resolution laser scanning microscope, so that the
micro-structure of an object transmitting or reflecting light, such as an
organic sample, can be observed, printed, or filed with an improved
resolution of approximately twice of that of the conventional diffraction
limited.
Preferably, in the first or third super-resolution scanning optical
apparatus, the first and second coherent light sources are a pair of
linearly polarized lasers which are arranged so that their planes of
polarization are perpendicular to each other.
Since a pair of linearly polarized laser beams are incoherent to each
other, they can easily be separated from each other through polarization
separation, so that the primary beam and subsidiary beam having planes of
polarization perpendicular to each other can be obtained by a simple
structure. In this case, since the primary beam and subsidiary beam can be
obtained by simply setting the light-emitting faces of the pair of
linearly polarized laser beams in specified alignment, the optical system
in use has a simpler structure.
Preferably, in each of the first to third super-resolution scanning optical
apparatus, the light separating means consists of a substrate the
refractive index of which is uniaxially anisotropic and a polarizing
holographic device or a polarizing diffraction grating so as to serve as a
polarization separating means for separating the light beam into the
primary beam and the subsidiary beam through polarization separation.
Since the polarizing holographic device or the polarizing diffracting
device transmits the major portion of the polarized beam of either one of
the primary and subsidiary beams as .+-. first-order diffracted beams,
while transmitting the polarized beam of the other of the primary and
subsidiary beams as a zero-order diffracted beam, the primary beam and
subsidiary beam can surely be separated in space so that the intensities
thereof can be detected individually. Thus, since polarization separation
can be implemented by means of a flat polarizing holographic device or a
flat diffraction grating, a more compact super-resolution scanning optical
system can be implemented at lower cost than in the case of using a
polarizing beam splitter.
Preferably, in the first or third super-resolution scanning optical
apparatus, the light separating means is composed of a multi-layer
dielectric filter so as to serve as a wavelength separating means for
separating the light beam into the primary beam and the subsidiary beam
through wavelength separation.
Since the multi-layer dielectric filter functions as a narrow-band pass
filter, the primary beam and subsidiary beam having wavelengths slightly
different from each other can be separated from each other efficiently due
to the transmittance characteristics of the narrow band pass filter, and
also by the reflectance of the inverse characteristics. In this case,
since the polarization characteristic can be determined selectively, the
optimum polarization characteristic required by the acoust-optical
deflector can easily be satisfied, so that a super-resolution scanning
microscope which enables real-time display can easily be implemented.
Preferably, in the second super-resolution scanning optical apparatus, the
polarizing phase plate separates the coherent beam emitted from the
coherent light source into an optical component having a plane of
polarization in one direction and an optical component having a plane of
polarization in another direction, the above planes of polarization being
perpendicular to each other, emits, as the primary beam, the optical
component having the plane of polarization in one direction, has a first
region which does not provide any relative phase difference to the optical
component having the plane of polarization in another direction and a
second region which provides a relative phase difference of .pi. to the
optical component having the plane of polarization in another direction,
and emits, as the subsidiary beam, the optical component passing through
the first and second regions.
The polarizing phase plate emits the primary beam having a plane of
polarization in one direction as it is, while providing a beam having a
plane of polarization in another direction with a relative phase
difference varying from 0 to .pi. so that it is emitted as the subsidiary
beam having peak intensities at least on both sides of the center thereof
and a principal portion equal in size to that of the primary beam.
Consequently, it becomes easy to scan the plane to be scanned with the
primary beam and subsidiary beam being superimposed upon each other, to
separate the light beam reflected from the plane to be scanned into the
primary and subsidiary beams again through polarization separation, and to
detect the intensities thereof individually. In this case, since the
primary beam and subsidiary beam are produced through polarization
separation, the intensity distributions in the peripheral portions of the
primary and subsidiary beams are the same in configuration, so that their
optical axes are not displaced from each other even when beam scanning is
performed. The output signal indicating the intensities of the primary and
subsidiary beams is differentially calculated, so that a scanning signal
which achieves super-resolution at least in one dimension can be obtained
extremely stably.
Preferably, the first and second regions are formed around the center of
the polarizing phase plate in four regions so that the two first regions
alternate the two second regions. Thus, it is possible to scan the plane
to be scanned with the light beam obtained by superimposing the primary
beam and the subsidiary beam having peak intensities in four directions
around the center thereof upon each other. After scanning, the light beam
is separated into the primary beam and subsidiary beam again through
polarization separation, so that the intensities thereof are detected
individually. Consequently, super-resolution scanning equivalent to the
scanning using an angular beam thinner than the diffraction limited can be
performed stably.
Preferably, in the first super-resolution scanning optical apparatus, the
phase plate is divided into N (N is an integer equal to or more than 2)
regions around the center thereof, the N regions providing a relative
phase difference advancing stepwise in the sequence of 0, 2.pi./N,
(2.pi./N).times.2, (2.pi./N).times.3, . . . , and (2.pi./N). (N-1) to the
second coherent beam emitted from the second coherent light source and
emits the second coherent beam passing through the N regions as the
subsidiary beam.
Preferably, in the second super-resolution scanning optical apparatus, the
polarizing phase plate separates the coherent beam emitted from the
coherent light source into an optical component having a plane of
polarization in one direction and an optical component having a plane of
polarization in another direction, the above planes of polarization being
perpendicular to each other, emits the optical component having the plane
of polarization in one direction without providing any relative phase
difference thereto, has N (N is an integer equal to or more than 2)
regions around the center thereof which provides a relative phase
difference advancing stepwise in the sequence of 0, 2.pi./N,
(2.pi./N).times.2, (2.pi./N).times.3, . . . , and (2.pi./N).(N-1) to the
optical component having the plane of polarization in another direction,
and emits, as the subsidiary beam, the optical component passing through
said N regions.
In this manner, the plane to be scanned can be scanned with the light beam
obtained by superimposing the primary beam and the subsidiary beam, which
has peek intensities around the center of the beam and which is coaxial
with the primary beam, upon each other. After scanning, the light beam is
subjected to polarization separation into the primary beam and subsidiary
beam so that the intensities thereof are detected individually.
Consequently, super-resolution scanning equivalent to the scanning using a
circular beam thinner than the diffraction limited can be performed
stably. Thus, by using the polarizing phase plate symmetrical with respect
to the axis, the first and second super-resolution scanning optical
apparatus, which are equivalent in performance to the super-resolution
beam scanning optical system symmetrical with respect to the axis, can be
implemented easily and stably with much advantage.
Preferably, in each of the first to third super-resolution scanning optical
apparatus, the scanning means has a pair of acoust optical deflectors for
deflecting the primary beam and the subsidiary beam in two directions
perpendicular to each other on the plane to be scanned. Thus, the scanning
means performs high-speed scanning in two directions perpendicular to each
other, so that a two-dimensional image can be obtained in real time.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view showing the structure of a super-resolution
scanning optical apparatus according to a first embodiment of the present
invention;
FIG. 2 is a schematic view illustrating, using a one-dimensional model, the
production of a subsidiary beam and the structural principle of the
super-resolution scanning optical system, which are common to all the
embodiments of the present invention;
FIG. 3 is a schematic view illustrating, using a simple one-dimensional
model, the principle of the super-resolution scanning optical system which
is common to all the embodiments of the present invention;
FIG. 4 is a schematic view showing the structure of the super-resolution
scanning optical apparatus according to a second embodiment of the present
invention; FIG. 5 is a schematic view showing the structure of the
super-resolution scanning optical apparatus according to a third
embodiment of the present invention; FIG. 6 is a schematic view showing
the structure of the super-resolution scanning optical apparatus according
to a fourth embodiment of the present invention;
FIG. 7 is a schema | | |
