US20170218521A1

US20170218521A1 - Fabrication of petal-shaped masks for suppression of the on-axis poisson spot in telescope systems

Info

Publication number: US20170218521A1
Application number: US15/275,839
Authority: US
Inventors: Ron Shiri; Jeffrey C. Livas; John G. Hagopian; Matthew T. Showalter; Thomas R. Stevenson
Original assignee: Individual
Current assignee: Individual
Priority date: 2016-01-19
Filing date: 2016-09-26
Publication date: 2017-08-03

Abstract

Aspects of the present disclosure involve a system and method for suppressing a Poisson spot. A Poisson spot is a bright spot in the geometrical shadow of circular/spherical shapes. A broad class of telescopes that involve simultaneous transmit and receive require suppression of the reflected light from the secondary mirror on the detector. In one embodiment, coronagraphy petal-shaped masks are fabricated using photolithography and wire-EDM for the suppression of the Poisson spot. The petal-shaped masks can be designed and fabricated to operate at varying Fresnel numbers and petal tip radius-of-curvature (ROC).

Description

PRIORITY

The present Application claims priority to Provisional Application 62/280,398, filed Jan. 19, 2016 which is herein incorporated by reference.

TECHNICAL FIELD

This disclosure relates generally to Poisson spot suppression, and more specifically to a method for suppressing a Poisson spot in a telescopic system using petal-shaped masks.

BACKGROUND

A Poisson spot is a bright light that appears in a geometrical shadow region of an object. The presence of the Poisson spot (spot of Arago) can be characterized as the interference of light waves diffracted on the edges of the obscuration with its central position determined by the symmetry of the object. In the past few years, various disciplines ranging from photonics to astronomy have focused their attention on characterizing the spot and particularly on suppressing the bright spot in order to obtain more precise interferometric measurements. For instance, the exoplanetary missions in search of Earth-like planets using direct imaging techniques require suppression of the broadband bright starlight on the telescope aperture. Additionally, the evolved Laser Interferometric Space Antenna (eLISA), a re-scoped version of the baseline LISA mission concept, if operated with an on-axis telescope design, requires suppression of the directly reflected laser source from the secondary mirror of the telescope assembly back onto the detector. These observatories study the source of gravitational waves from 0.0001 Hz to 1 Hz by monitoring the path length difference between pairs of free falling test masses with laser interferometry and thus a precision of picometers over gigameter baselines is often necessary. However, corresponding disciplines have yet to identify a method for suppressing the Poisson spot in orders of magnitude.

BRIEF SUMMARY

The present disclosure is directed to a system and methods for suppressing a Poisson spot on a device. A bright spot (Poisson) can be present on a telescope detector when a symmetrical object placed on near-field region of the telescope obstructs a coherent light source in ‘transmission’. The presence of the petal-shaped mask in place of the symmetrical object along the optical axis of the telescope suppresses the bright spot on the detector considerably.
Another method that a Poisson spot could appear on a telescope detector is when a reflected beam from a secondary mirror is blocked by a symmetrical shape in a near-field configuration. The presence of the petal shaped mask on the surface of the mirror along the optical axis suppresses this bright spot.
The system may include a coherent source device that can transmit a laser beam to a mirror and reflected to a detector placed at the Fresnel Zone. A symmetrical obstruction at the center of the mirror creates a bright spot on the detector. The system can further include fabricated petal shaped mask using one of a photolithography process. The petal shape mask can suppress the Poisson spot created by the reflected laser beam.

BRIEF DESCRIPTION OF THE DRAWINGS

The description will be more fully understood with reference to the following figures and data graphs, which are presented as various embodiments of the disclosure and should not be construed as a complete recitation of the scope of the disclosure, wherein:

FIG. 1 is a diagram illustrating a ‘transmission’ system with a Poisson spot.

FIG. 2 is a diagram illustrating microscopic images of fabricated petal-shaped masks using photolithography.

FIG. 3 is a diagram illustrating microscopic images of fabricated petal-shaped masks using Wire Electrical Discharge Machining (EDM).

FIG. 4 is a flow chart of a method for suppressing a Poisson spot in ‘transmission’ using petal-shaped masks.

FIG. 5A is a diagram illustrating various sizes of petal-shape masks in flywheel radial arrangement.

FIG. 5B is a diagram illustrating an optical test bed setup for intensity suppression testing of the flywheel petal-shaped masks.

FIG. 6A is a graph illustrating relative intensity measurements for a 12-petal mask along the optical axis

FIG. 6B is comparison of relative intensity cross-profile on the detector. The three curves show the laser source intensity, Poisson spot presence when a circular mask is used, and petal-shaped mask is used.

FIG. 7 is a flow chart of a suppressing a Poisson spot in ‘reflection’.

DETAILED DESCRIPTION

Aspects of the present disclosure involve systems, methods, devices and the like for suppressing a bright Poisson spot from the shadow of an object. In one aspect, coronagraphy petal-shaped masks are fabricated using photolithography for the suppression of the Poisson spot. In another embodiment, coronagraphy petal-shaped masks are fabricated using wire electrical discharge machining (EDM) for the suppression of the Poisson spot. The petal-shaped masks can be designed and fabricated to operate at varying Fresnel numbers and petal tip radius-of-curvature (ROC).
FIG. 1 is a diagram illustrating a transmission system 100 with a Poisson spot 108. A Poisson spot 108 is a bright spot that appears at the center of a shadow when a laser beam or other coherent light shines on a symmetrical object 104. Illustrated in FIG. 1, is Poisson spot 108 appearing on a screen 106 as a light (e.g., beam) from a source 102 is pointed at a symmetrical object 104. The bright spot (e.g., Poisson spot 108) can appear due to light diffraction. The light from source 102 can hit the surface of the object 104. On the circumference of the object 104, a new point source from every point of object is created that goes towards the center of the shadow of the object 104 creating the bright spot. The diffraction of light from the edges of the object form a bright spot on the detector once placed in a Fresnel zone. This is an indication of the wave nature of the light as predicted.
In space missions that use of space antennas (e.g., Laser Interferometry Space Antenna LISA), Poisson spots 108 are often observed. In particular, Poisson spots 108 are observed in space antennas and other broad classes of telescopes that involve simultaneous transmit and receive of information and operate in the infrared region with an on-axis design. This commonly could occur if the reflected laser source from the optical telescope's secondary mirror is obstructed by a symmetrical object.
To suppress the Poisson spot 108, hypergaussian functions with petal shaped realizations have been used. FIG. 2 presents the design of coronography petal-shaped masks 200 for the suppression of the Poisson spot.
Coronography is the use of a device to block light (e.g., laser beam) on the center of a telescope. In one embodiment, the coronagraph can be a telescopic attachment that may be designed to block the laser beam reflected on the detector. For example, the telescopic attachment may come in the form of a symmetrical petal shaped mask 200 that blocks the light from the center while permitting light surrounding the source 104 to pass through relatively uninterrupted.
Since hypergaussian functions with petal shaped realizations have proved effective, the coronography petal shaped masks are fabricated with petals using varying hypergaussian functions. In particular, various coronography petal shaped masks were fabricated with varying petals shapes and petal tip radius-of-curvature (ROC) to evaluate the fidelity of the masks and fabrication process. FIG. 2 illustrates microscopic images of series of fabricated coronography petal-shaped masks 202-212 using photolithography for the suppression of the Poisson spot 108.
Because the fabricated petal-shaped masks can be placed on the secondary mirror of a telescope with <0.5 m primary aperture, the petal-shaped masks can be fabricated with diameters of a few millimeters. For example, FIG. 2 illustrates three sets of masks 202, 206, and 210 with a 2 mm, 5 mm and 10 mm diameter respectively. The transmission masks 202-212 are chromium and aluminum fabricated masks on 4×4 in. fused silica substrate. Mask 202 is a fabricated with 6 petals, and 2 μm tips and has a zoomed microscopic image 204. Mask 204 is a 5 mm mask fabricated with 16 petals and 200 μm tip and has a zoomed microscopic image 208. Mask 212 is a 10 mm mask with 12 petals and a 20 μm tip and a zoomed microscopic image 212.
As indicated, the masks 202-210 were fabricated using photolithography. In the photolithography process, the patterns are transferred from photomask to photoresist on the substrate with sputter deposition of chromium or aluminum. FIG. 2 shows the fabricated set of masks 202-210 on fused silica substrate. In order to avoid any signs of transmission through the mask once illuminated with 1064-nm laser source, a 300-nm thick aluminum layer coated with 50 Å of MgF3 as anti-reflection (AR) coating on 500-μm thick substrate can be employed.
For testing purposes, two variables in the petal shaped masks 200, can be adjusted: 1) the diameter and 2) the radius of curvature of the petal tips. Table I illustrates various masks fabricated on the substrate. Each row on Table I contains designed and measured ROC of the petal tips in microns followed by the diameter in millimeters, targeted Fresnel number, and number of petals on the mask.

TABLE I

Designed dimensions and petal tip sizes of masks fabricated using photolithography.
The boldface catrics are the most agreeable masks that could be fabricated using
photolithography.

Mask	Petal outer	Measured petal	Mask diameter	Measured mask	Fresnel	Number of
number	ROC (μm)	outer ROC (μm)	(mm)	diameter (mm)	number	petals

2.1	2	6	2	2.0	4.7	8
2.2	200	127	2	2.0	4.7	16
2.3	20	18.4	2	2.0	4.7	12
2.4	2	4.5	2	2.0	4.7	12
2.5	2	2	2	2.0	4.7	6
5.1	2	3.7	5	4.9	29.3	6
5.2	2	5.7	5	5.0	29.3	12
5.3	20	27.5	5	5.0	29.3	12
5.4	200	168	5	5.0	29.3	16
5.5	2000	767	5	5.0	29.3	8
10.1	2	3	10	9.9	117.2	6
10.2	2	6	10	9.9	117.2	12
10.3	20	20	10	10.0	117.2	12
10.4	200	192	10	10.0	117.2	16
10.5	2000	806	10	10.0	117.2	16

As indicated, the masks were designed to employ varying hypergaussian functions. As such, the hypergaussian function employed for these masks is designed specifically for suppression range of 2-4 orders of magnitude. As an example, for testing purposes, the Fresnel number range of 4.7-120 is selected for the geometry of the on-axis design of the eLISA telescope, as illustrated in Table I.
In addition, as indicated 2 mm, 5 mm and 10 mm masks can designed and used for the suppression of a Poisson spot observed in space antennas (e.g., Laser Interferometry Space Antenna (LISA)). For example, as illustrated in Table I, the 2-mm diameter masks are designed with 6, 8, 12, and 16 petals. The shape of each mask is specifically designed to maintain sharpness of the petal tips between 2 and 200 μm and designed to suppress the intensity at Fresnel number of 4.7. The fabricated masks on substrate are photographed under microscope and the outer ROC of petal tips is recorded, as illustrated in FIG. 2 with the 6-petal mask showing the closest agreement with the designed 2-μm tip. The outer ROC of the petal tips on the fabricated 8, 12, and 16-petal masks shows less agreement with the prescribed tip ROC.
The 5-mm diameter masks in this set have the same number of petals as the smaller 2 mm size masks. However, the petal tips are designed between 2-μm and 2-mm in radius with a targeted Fresnel number is 29.3. An examination of the masks shows the larger petal tips in least agreement between the measured outer ROC and prescribed petal tip radius. Therefore, a smaller ROC may provide am improved agreement with the design.
The 10-mm diameter masks have 6, 12, and 16 petals. The tips sharpness range from 2 μm to 2 mm. The targeted Fresnel number in this set is 117.2. A close inspection of this set shows the most agreeable masks to the designed criteria. Therefore, as the number of petals increases and the ROC of the tip increases, there is less agreement between the prescribed tips and the measured tips. However, as indicated in bold in Table 1, agreeable ROC results were observed between the designed and measured tips indicating the use of petal-shaped mask that are fabricated using photolithography can provide adequate Poisson spot intensity suppression. FIGS. 6A and 6B below provide further details regarding the results achieved using photolithography for the fabrication of the petal-shaped masks.
Like FIG. 2, FIG. 3 is a diagram illustrating microscopic images of fabricated petal-shaped mask for the suppression of a Poisson spot. In particular, FIG. 3 illustrates the microscopic images of petal shaped masks fabricated using Wire Electrical Discharge Machining (EDM). Wire EDM is an electro thermal production process in which thin single-strand metal wire in conjunction with deionized water enables cutting through metallic materials by the use of heat from electrical sparks. The EDM machining works by creating an electrical discharge between the wire or electrode and the workpiece. As the spark jumps across the gap, the material is removed from both the workpiece and the electrode. To stop sparking process from shorting out, a non-conductive fluid or dielectric (deionized water) is also applied. The wire does not touch the workpiece so there is no physical pressure on the surface and it prevents the damage and distortion. Because of the inherent properties of the process, the wire EDM can easily machine complex parts and precision components out of hard conductive materials. The final masks using wire-EDM required ultrasonic cleaning to remove the residues from the boundaries of the mask. Handling of these masks is very delicate and petal tips with 30 μm can be susceptible to breakage.
Table II shows the dimensions of the masks manufactured using wire EDM. Four sets of 8 and 16-petal masks were fabricated as illustrated in Table II with 30-67 μm radius of curvature for a designed 20-μm tip. The masks designed in this technique were targeted toward the Fresnel number of 7.3.

TABLE II

Mask shapes manufactured using wire EDM. The a.12 and a.22 masks share same
outer radius of curvature but deeper inner radius of curvature.

Mask	Petal outer	Measured petal	Mask diameter	Measured mask	Fresnel	Number of
number	ROC (μm)	outer ROC (μm)	(mm)	diameter (mm)	number	petals

a.11	20	67	5	5.0	7.3	8
a.12	20	50	5	5.0	7.3	8-Ext
a.21	20	34	5	5.0	7.3	16
a.22	20	30	5	5.0	7.3	16-Ext

FIG. 3 illustrates a set of petal-shaped masks fabricated using the wire EDM. The aluminum masks are about 1 mm thick and have a 5 mm in diameter. As illustrated in FIG. 3, two sets of masks 302, 304 with 8 and 16 petals are manufactured with differing sharpness of the inner radius of curvature as visible in the zoomed microscopic images 304,306. The inner radius of curvature refers to the spacing where each petal is attached to the main body of the mask. Therefore, 8 petal-shaped mask 302, 304 has a greater ROC than the 16 petal-shaped mask 306,308. By differing the ROC on the petal shaped masks 302,306 the performance of the wires in the tight space between the petals could be assessed. In one embodiment, wire EDM is used to fabricate petal-shaped masks for the suppression of Poisson spot 108 in laser interferometry. The wire EDM fabricated petal-shaped masks can enable improved suppression while proving the fabrication need for the sharp petal tips of the masks.
FIG. 4 is a flowchart of the various operations of the presently disclosed technology. Specifically, FIG. 4 is a flow chart of a method for suppressing a Poisson spot using petal-shaped masks. Method 400 begins with operation 402, where a Poisson spot is encountered and observed by a detector or other device. As previously indicted, a Poisson spot may be present in optical telescopes for space-based laser interferometry because the laser source from the optical telescope's secondary mirror is reflected on the detector. In general, in interferometry, telescopes use a laser source to transmit a laser beam or other coherent light toward a beam splitter. The beam splitter can split the transmitted laser beam into two beams. Each beam then get transmitted or reflected in the direction a mirror. The mirrors then reflect back the beams, where they are recombined at the beam splitter before reaching a detector. The mirrors ensure the beams are in parallel and can recombine with each other at the beam splitter. The recombined beam then reaches the detector where the beams interfere with each other constructively or destructively.
To suppress the bright spot created by the reflected beam, method 400 continues to operation 404, where a petal shaped mask is positioned relative to or in proximity to the telescope's secondary mirror to block the reflected laser light or beam. In particular, a petal-shaped mask is used as a telescopic attachment and intended to be placed on the secondary mirror of a telescope to suppress the Poisson spot. The petal-shaped mask may be placed by an individual, a computer, a controller, or other device. In some instances, the petal-shaped masks are fabricated using photolithography. Photolithography is a microfabrication process that uses light to transfer patterns from a photomask to a photoresist, light-sensitive chemical on a substrate. As an example, the petal shaped masks can be fabricated using a chromium or aluminum on quartz substrate. These photolithography fabricated petal shaped masks are designed to suppress the Poisson spot intensity in the order of 2 to 4 orders of magnitude.
In other instances, the petal-shaped masks are fabricated using wire-EDM. Wire-EDM is an electro thermal production process in which thin single-strand metal wire in conjunction with deionized water enables cutting through metallic materials by the use of heat from electrical sparks. The EDM machining works by creating an electrical discharge between the wire or electrode and the workpiece. The wire EDM fabricated petal-shaped masks can be designed to suppress the Poisson spot while providing the fabrication need for the sharp petal tips of the masks.
Once the fabricated petal shape mask is in place, method 400 continues to operation 406, where the Poisson spot created by the reflection of the second mirror in the telescope is suppressed by the positioning of the mask. Note the fabrication used, the Fresnel number, and the diameter of the mask can be varied based on the application needs.
To test the various petal-shaped masked fabricated, a flywheel with the various petal-shaped masks was created and evaluated. FIGS. 5A and 5B illustrate an exemplary flywheel of masks 500 and corresponding testbed 502 for the evaluation of the petal-masks. As illustrated in FIG. 5A, the flywheel of masks 500 can include a radial arrangement of the various petal-shaped masks fabricated on silica wafer. As an example, the flywheel mask 500 can correspond to the petal-shaped masks described above and in conjunction with FIG. 2 and Table 1. For example, mask 10.3 corresponds to a 6 petal mask with good ROC agreement (outer ROC and measured ROC are 20 m), a mask diameter of 10 mm, and Fresnel number of 117.2.
To ensure proper functionality, the petal masks are evaluated on a testbed where intensity measurements can be taken. In particular, FIG. 5B is a diagram illustrating an optical testbed setup 502 for intensity suppression testing of the flywheel petal-shaped masks (e.g., flywheel of masks 500) fabricated. Note that for the performance measurements, the testbed 502 can be set up to include any configuration and instrumentation.
In one exemplary configuration, the testbed 502 can be designed to include an optical bench 506 with a laser source 508, the flywheel of masks 500, and detector 504. The flywheel of masks 500 can be mounted on a pedestal post 510 along an optical axis between laser source 508 and detector 504. The laser source can produce, for example, a 1064 nm beam and be 1000 mm away from the detector 504. In addition, the detector 504 can be a Coherent LaserCam-HR progressive scan CMOS detector with 6.7 μm pixel size for detecting the beam transmitted by the laser source 508.
To initiate the testing, any ambient light is removed from the presence of the detector 504. To remove the ambient light, it is first captured by taking a series of dark images while the overhead lights and laser source are turned-off. These images can subsequently be subtracted from the images of the laser source 508 and the mask images as “background.”
Next, the testing continues by collimating the laser beam before it covers the whole area of the flywheel of masks 500 and the detector 504. Collimation of the light includes ensuring the light rays of the laser beam 510 remain parallel to make certain minimal dispersion occurs during propagation. Additionally, used to produce a one-inch diameter laser beam 510. In one instance, the beam expander can be visually checked using a shear plate.
Then, the expanded laser beam 510 is transmitted toward the direction of the detector 504, hitting the flywheel of masks 500 which is positioned between the detector 504 and the laser source 502. The position of the flywheel of masks 500 can be varied from 27 cm to 82 cm away from the detector 504. This is equivalent to Fresnel number between 4.7 and 120. The relationship between Fresnel number and the distance between detector 504 and flywheel of masks 500 is derived from z=R2/fλ, where R is the radius of the mask, f is the Fresnel number, and λ is the wavelength of the incident beam 510.
FIGS. 6A-6B providing exemplary performance results obtained using a test bed setup similar to testbed 502 as described above and in conjunction with FIG. 5B. FIG. 6A includes a graph illustrating the relative intensity measurements for a 12-petal mask. While FIG. 6B is a diagram illustrating the intensity suppression measurements of the 12-petal mask.
In one embodiment, a subset of 2-mm diameter mask (mask 2.3 from Table I) fabricated using photolithography was evaluated in this setup by rotating the flywheel of masks 500 and aligning the desired target mask into the optical path between the laser source 508 and the detector 504. This setup allows quick insertion and change of the mask into the laser beam 510 path. The manufacturing tolerance on the petal tips is about 1/10 of μm. In some instances, an improved performance can be achieved where closely spaced high-resolution printing nozzles and accurate tracking and scaling capabilities exist. Thus, photolithography provides improved performance.
In FIG. 6A, the optical performance of the masks is measured and compared against the mathematical model. As seen in FIG. 6A the logarithm of the relative intensity suppression 600 is illustrated. The relative intensity suppression 600 can generally be defined as the ratio of the intensity at the shadow to the intensity of the incident beam. In FIG. 6A, the relative intensity suppression 600 for the 2-mm diameter 12-petal mask (e.g., mask 2.3 from Table I) is diagramed. In the testbed 502, the mask was positioned along the optical axis and varied from 27 cm to 82 cm. As illustrated, the measured intensity (dashed line) qualitatively follows the prediction (solid line) as expected. The maximum suppression of about 4 orders of magnitude occurs at z=27 cm. Results indicate scattered light problems may be resolved with improved performance at shorter distances.
In FIG. 6B, the cross section profile of the intensity suppression 602 in the shadow region was also measured at each position along the optical axis. Specifically, in FIG. 6B, the intensity across the 12-petal mask at 27 cm away from the detector 504 was compared. The plot shows the intensity suppression 602 of incident laser beam 510 (solid line arcing about the 0 axis), circular mask (dashed line), and 12-petal mask (solid line). Intensity suppression measurements 602 illustrates the presence of a Poisson spot in the shadow of the circular mask, and successful suppression by the 12-petal mask (e.g., mask 2.3 from Table I) by 4 orders of magnitude across the petal mask. Note that the measured suppression at the shadow region may be limited to the dynamic range use.
As illustrated in FIGS. 6A-6B photolithograph-fabricated aluminum masks on fused silica wafer can produce a more accurate and sharp petal tips, even at 2-μm. In one embodiment, one-sided AR coated substrate deposited with 300-nm thick aluminum was used and shows no signs of transmission leakage of the laser source through the mask. The position of the mask relative to the detector 504 was adjusted to produce Fresnel numbers from 4.7 to 120. Results demonstrated a good agreement between the prediction and the experiment. Further, the efficacy of the mask was verified against the against the analytical model by measuring the highest suppression (4 orders of magnitude) at the position of the mask placed 27 cm away from the detector, closely following the prediction model.
Table III shows a summary of fabrication techniques and achievable ROC for outer petal tips using photolithography and EDM.

TABLE III

Summary of fabrication techniques and achievable petal tip ROC.

	Diameter of	Achievable petal	Mask material	Edge smoothness
Method of fabrication	mask (mm)	outer ROC	and thickness	(μm)	Remarks

High-resolution	50	0.1-5	mm	Pigmented ink on mylar	>100	High-resolution printer masks
printers				~500 μm		have rough edges and large
						spatial gaps on the surface that
						make them impractical for optical
						testing
3D printers	15-50	0.5-5	mm	Polymer resin 0.5-2 mm	>100	3D printing masks have imperfect
						rough boundaries that are far
						from the prescribed models
						making them of a lower quality
						unsuitable for optical testing
Photo lithography	2-10	2-5	μm	Chromium 60 nm and	<1	Lithography achieves the best
				aluminium
300 nm on		result when mask diameter is
				fused silica		small with smooth edges and
						sharp tips. This is the best
						technique out of the ones we have
						investigated and it is scalable
EDM	5	20	mm	Aluminium 1 mm	>1	The EDM manufacturing was
						conducted only on 5 mm
						diameter masks. This technology
						is not mature enough to achieve
						smooth edges suitable for optical
						performance

The petal shaped masks 202-212 and 302-3087 of FIGS. 2-3 are possible examples of a coronagraphy masks that may be employed or be configured in accordance with aspects of the present disclosure. In addition, other possible fabrication techniques can be used for generating the petal-shaped mask including, but not limited to, high resolution printing and 3D printing. Still further, it will be appreciated that other configurations may be utilized. For example, use of carbon nanotubes may be used for coating the masks and the dynamic range of the detector may be modified.
In addition, the method for suppressing the Poisson spot using the petal shaped masks may be varied. For example, FIG. 7 is a secondary flow chart of a method for suppressing a Poisson spot using petal-shaped masks. Method 700 begins with operation 702, where a coherent light beam (e.g., laser beam) is transmitted by a light source. As previously indicted, telescopic instruments are generally used in making interferometric measurements and as such a light source, a splitter, and at least measured and reflected mirrors are often present.
In operation 704, the coherent light is transmitted in the direction of a beam splitter where the coherent light is split into at least two beams, a first beam and a second beam. In operation 706, the beam splitter can then reflect each beam in a direction of a mirror. For example, the first beam can be reflected to a first mirror (e.g., measured mirror) and the second beam can be reflected to a second mirror (e.g., reflected mirror). Each of the mirrors can then receive the corresponding beams and reflect them back in the direction of the beam splitter.
At the beam splitter, the at least two beams are combined for transmission to a device (e.g., detector), in operation 708. The mirrors ensure the beams are in parallel and can recombine with each other at the beam splitter. The recombined beam then reaches the device/detector where the beams interfere with each other constructively or destructively to generate interference fringes that can be analyzed.
In some instances, one of the beams reflected from one of the mirrors of the telescope can reflect onto the detector causing a Poisson spot to appear. In particular, in operation 710, the secondary mirror from the telescopic instrument can reflect a beam toward device to create the Poisson spot. As indicated, the Poisson spot can hinder the ability to perform precise interferometric measurements; therefore a petal shaped mask can be fabricated to suppress the Poisson spot.
To suppress the bright spot created by the reflected beam, method 700 continues to operation 712, where a petal shaped mask is positioned relative to or in proximity to the telescope's secondary mirror to block the reflected laser light or beam. In particular, a petal-shaped mask is used as a telescopic attachment and intended to be placed on the secondary mirror of a telescope to suppress the Poisson spot. The petal-shaped mask may be placed by an individual, a computer, a controller, or other device. In some instances, the petal-shaped masks are fabricated using photolithography or wire-EDM. Once the fabricated petal shape mask is in place the Poisson spot created by the reflection of the second mirror in the telescope is suppressed by the positioning of the mask. Note the fabrication used, the Fresnel number, and the diameter of the mask can be varied based on the application needs.
In another aspect, the method can include a reduced number of steps from what is shown in FIG. 7. The method could include any one or more of the steps shown in FIG. 7. For example, the method can include transmitting a coherent light source such as a laser, receiving a beam by a mirror fabricated with petal-shaped masks and detecting where a Poisson spot is suppressed.
In the present disclosure, the methods disclosed may be implemented as sets of instructions in hardware or software. It may be further understood that the specific order or hierarchy of steps in the methods disclosed are instances of example approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the method can be rearranged while remaining within the disclosed subject matter. The accompanying method claims present elements of the various steps in a sample order, and are not necessarily meant to be limited to the specific order or hierarchy presented.
While the present disclosure has been described with reference to various implementations, it will be understood that these implementations are illustrative and that the scope of the present disclosure is not limited to them. Many variations, modifications, additions, and improvements are possible. More generally, embodiments in accordance with the present disclosure have been described in the context of particular implementations. Functionality may be separated or combined in blocks differently in various embodiments of the disclosure or described with different terminology. These and other variations, modifications, additions, and improvements may fall within the scope of the disclosure as defined in the claims that follow.

Claims

What is claimed is:

1. A method comprising:

transmitting, to a detector, a reflected beam from a mirror of a telescopic instrument obstructed by a symmetrical object, to yield a transmitted and reflected beam, wherein a Poisson spot is formed on the detector;

fabricating a petal shaped mask on a surface of the mirror using one of a photolithography process and stand alone electrical machining process; and

suppressing by the petal shaped mask the Poisson spot created by the transmitted and reflected beam.

2. The method of claim 1, wherein the reflected beam is from a secondary mirror of the telescopic instrument.

3. The method of claim 1, wherein the telescopic instrument is a space antenna.

4. The method of claim 1, wherein the petal shaped mask is fabricated using the photolithography process and wherein the photolithography processes uses a chromium substrate.

5. The method of claim 1, wherein the petal shaped mask is fabricated using the electrical machining process and wherein the electrical machining process uses thin single-strand metal wire in conjunction with deionized water.

6. The method of claim 1, wherein the petal shaped mask is between 2 mm and 50 mm in diameter.

7. The method of claim 1, wherein the petal shaped mask suppresses an intensity of the Poisson spot along an optical axis of the telescopic instrument with a Fresnel number between 4.7 and 120.

8. The method of claim 4, wherein the petal shaped mask includes a 2 μm petal tip.

9. A system comprising:

a source device, the source device configured to transmit a laser beam in a direction of a mirror and wherein the mirror receives the laser beam, reflects the laser beam in a direction of a device, wherein the laser beam reflected in the direction of the device creates a Poisson spot; and

a controller that positions a petal shaped mask in proximity to the mirror, wherein the petal shaped mask is fabricated using one of a photolithography process and an electrical machining process, wherein the petal shaped mask is configured to suppress the Poisson spot created by the reflected laser beam.

10. The system of claim 9, wherein the system is a space antenna.

11. The system of claim 9, wherein the petal shaped mask is fabricated using the photolithography process and wherein the photolithography processes uses a chromium substrate.

12. The system of claim 9, wherein the petal shaped mask is fabricated using the electrical machining process and wherein the electrical machining process uses thin single-strand metal wire in conjunction with deionized water.

13. The system of claim 9, wherein the petal shaped mask is between 2 mm and 50 mm in diameter.

14. The system of claim 9, wherein the petal shaped mask suppresses an intensity of the Poisson spot along an optical axis of a telescopic instrument with a Fresnel number between 4.7 and 120.

15. The system of claim 11, wherein the petal shaped mask includes a 2 μm petal tip.

16. A method comprising:

transmitting, by a light source, a coherent light beam;

receiving a reflected beam associated with the coherent light beam from a mirror at a device, wherein the reflected beam creates a Poisson spot;

attaching, by a controller, a petal shaped mask in proximity to the mirror, wherein the petal shaped mask is fabricated using one of a photolithography process and an electrical machining process; and

suppressing, by the petal shaped mask, the Poisson spot created by the reflected beam.

17. The method of claim 16, wherein the petal shaped mask is fabricated using the photolithography process and wherein the photolithography processes uses a chromium substrate.

18. The method of claim 16, wherein the petal shaped mask is fabricated using the electrical machining process and wherein the electrical machining process uses thin single-strand metal wire.

19. The method of claim 16, wherein the petal shaped mask is between 2 mm and 50 mm in diameter.

20. The method of claim 17, wherein the petal shaped mask includes a 2 μm petal tip.