Optical: systems and elements – Single channel simultaneously to or from plural channels
Reexamination Certificate
2001-01-25
2003-08-26
Mack, Ricky (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
C359S629000, C359S637000, C353S035000
Reexamination Certificate
active
06611379
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a beam splitter and method for generating equal optical path length beams for interferometry and other metrology applications. More particularly, the present invention is primarily directed to a beam splitter that has a monolithic structure and exhibits improved stability. The invention is particularly useful for generating parallel beams with a well defined lateral separation for a variety of applications including: surface profiling, precise angle monitoring, pencil beam interferometer and shearing interferometry.
Devices for generating parallel pencil beams are well known in the art. U.S. Pat. No. 4,498,773 to von Bieren discloses an interferometer which measures optical surfaces through the interference of two pencil beams which are reflected off an optical surface. The interferometer includes a laser for generating a laser beam which is split into two parallel beams by a beam splitter and a mirror. The two pencil beams are reflected off a second beam splitter through an alignment invariant optical device and onto the optical surface to be measured. The two pencil beams are reflected and back-trace through the alignment invariant optical device, propagate through the second beam splitter and enter an optical lens. The optical lens focuses the two beams in its back focal plane where the interference of the two pencil beams takes place. This information is then relayed through an optical spatial filter and optional micro objective into a readout section.
U.S. Pat. No. 4,884,697, which issued to the same inventors of the present invention and is commonly assigned, discloses a long-trace surface profiler for non-contact measurement of surface profile, slope error and curvature on cylindrical synchrotron radiation (SR) mirrors. The optical system is based upon the concept of a pencil-beam interferometer with an inherent large depth-of-field. The optical system uses a zero-path-difference beam splitter, which separates a laser beam into two collinear, variable-separation probe beams. A linear array detector is used to record the interference fringe in the image, and analysis of the fringe location as a function of scan position allows one to reconstruct the surface profile. The optical head is mounted on an air-bearing slide with the capability to measure long aspheric optics, typical of those encountered in SR applications. The optical system also uses a transverse outrigger beam which provides information on the relative alignment of the scan axis to the cylinder optic symmetry axis. The disclosure of U.S. Pat. No. 4,884,697 is incorporated herein by reference.
U.S. Pat. No. 5,446,710 to Gardner et al. discloses a focus error detection using an equal path length lateral shearing interferometer. As shown in
FIGS. 2
,
5
A, and
5
B, the interferometer
50
includes a beam splitter
52
and two abutting roof prisms
54
and
56
. The roof prisms
56
,
54
can be shifted along an axis orthogonal to the direction of light propagation and to the peak of the roof creates a lateral shear between the two output beams as shown in FIG.
5
A. The roof prism may also be rotated about an axis producing a tilt between the two output beams as shown in FIG.
5
B. This creates an interference pattern with a rotational orientation which is a function of the focus of the beam impinging on the optical storage medium. A pattern sensor is provided to adjust the focus of the beam in an accurate and dynamic manner.
U.S. Pat. No. 4,783,170 to Bergstrom discloses a symmetrical prismatic readout apparatus for a ring laser gyro using a platinum beam splitter. The readout apparatus includes a pair of substantially identical prism elements
12
and
14
. The prism elements have sides
16
,
18
,
24
and
26
that are parallel and are perpendicular to sides
20
and
28
as shown in FIG.
1
. The fourth side of each prism element is oriented at a 45 degree angle with respect to the parallel sides. Both the first and second prisms
12
and
14
are substantially identical in construction and are arranged so that sides
20
and
28
are collinear. A beam splitter coating
32
,
34
is applied to the fourth side
22
,
30
of the prism elements
12
,
14
. A beam splitter
36
is also imposed at the interface between the two prisms
12
and
14
. The apparatus includes a reflector element
6
having an inner surface
38
that is also a beam splitter.
U.S. Pat. Nos. 5,548,403 and 5,933,236 to Sommargren disclose phase shifting interferometers. More specifically, U.S. Pat. No. 5,548,403 discloses a phase shifting interferometer that uses a spherical wavefront generated by the process of diffraction.
FIG. 1
in both of the references are the same and illustrate that which is pertinent to the present invention. In particular, the interferometers include a beam splitter
22
having a pair of fixed retroreflectors
24
and
28
arranged in a similar fashion to the cube beam splitter and right angle prisms in U.S. Pat. No. 4,884,697 discussed above.
U.S. Pat. No. 4,743,188 to Tsuchiya et al. discloses a method of detecting origin of shear and measuring amount of shear in shearing interferometer systems. Referring to
FIG. 1
, this patent also discloses an arrangement that is similar to the disclosure in U.S. Pat. No. 4,884,697 and includes a beam splitter
18
corner-cube prisms
20
,
22
. The patent also includes a pair of shutters
21
,
23
located between the beam splitter
18
and the corner-cube prisms
20
,
22
.
The problems associated with the prior art parallel beam generators include: the prior art apparatuses are not equal optical path length apparatuses thus causing instability of the measurement produced by frequency shift of the light source, or the apparatuses are subject to thermal drift and subject to additional stability problems associated with the relative mechanical vibration and slow shifting of their optical components, or both. The present invention addresses these problems through a monolithic structural design and generation of equal optical path length beams. In addition, the beam splitter in accordance with the present invention is compact, which is advantageous in certain metrology applications.
SUMMARY OF THE INVENTION
The present invention is a beam splitter for splitting an incident beam into first and second beams so that the first and second beams have a equal optical path length, fixed lateral separation, and are parallel upon exiting. The beam splitter includes a first prism, a second prism, and a film located between the prisms. The first prism is defined by a first thickness and a first perimeter which has a first major base. The second prism is defined by a second thickness and a second perimeter which has a second major base. The film is located between the first major base and the second major base for splitting the incident beam into the first and second beams.
In a preferred embodiment, the first and second perimeter are trapezoidal shaped. In this embodiment, the first perimeter also includes a first minor base, a first reflecting side, and a first nonreflecting side. The first reflecting side preferably forms a right angle with the first major base. Similarly, the second perimeter includes a second minor base, a second reflecting side, and a second nonreflecting side. The second reflecting side preferably forms a right angle with the second major base. Preferably the first nonreflecting side intersects the first major base a 45 degree angle and the second nonreflecting side intersects the second major base at a 45 degree angle. Preferably the first nonreflecting side and the second nonreflecting side are arranged to intersect at a right angle. Preferably the first major base is shorter than the second major base and the film has ratio of 1:1 between transmissivity and reflectivity after gluing.
In accordance with the present invention a method of generating beams includes providing a beam splitter and directing an incident beam at the beam splitter. The beam splitter includes trapezoidal shaped f
Qian Shinan
Takacs Peter
Bogosian Margaret C.
Brookhaven Science Associates LLC
Mack Ricky
LandOfFree
Beam splitter and method for generating equal optical path... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Beam splitter and method for generating equal optical path..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Beam splitter and method for generating equal optical path... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3101194