SPECTROMETRIC IMAGER

• US 3,720,469 A
• Filed: 01/25/1971
• Issued: 03/13/1973
• Est. Priority Date: 01/25/1971
• Status: Expired due to Term

• Current Assignee: Martin Harwit
• Original Assignee: Martin Harwit
• Inventors: Harwit, Martin
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Evans, F. L.
• Application Number:
  US05/109,432
• Time in Patent Office: 778 Days
• Field of Search: 250/237R,237G 356/74,76-79,96-98
• US Class Current: 356/310
• CPC Class Codes: G01J 3/2823 Imaging spectrometer
• CPC Class Codes: G01J 3/2846 using modulation grid; Grid spectrometers

Abstract

An optical device modulates radiation such as light from an extended object and focuses it onto a single detector in such a way that the modulation gives both spatial resolution of different points on the object and spectral resolution of light coming from each point on the object. The signal received by the detector can then be demodulated to reconstruct both the spatial and spectral properties of the initial extended object. A mask pattern is used, which can be variably exposed in successive steps to produce a cyclic encoding pattern in two dimensions. For an image resolved into p X m elements, the mask need only have (2p-1) (2m-1) elements, instead of p2 X m2 modulating elements.

Claims

1. Apparatus for sequential production of a series of signals which series represents the value of electromagnetic radiation energy levels distributed over an area comprising means for imaging the area, means for sensing the energy of the imaged area to produce electrical signals in response to radiation incident thereupon, optical means between the imaging means and the sensing means for selectively transmitting energy from portions of the area to the sensing means including a first modulating mask with an array of a plurality of rows of at least two spaces in each and a total of at least (2p-1)(2m-1) spaces where p and m are integers of substantial value such that the product p X m can represent the desired number of areal elements required for a predetermined accuracy of spatial resolution, means to expose a succession of rectangular groups, each group comprising p X m of such spaces, approximately one-half of said spaces of said mask being opaque, and the remaining spaces non-opaque, the opaque spaces being so located that in each exposed rectangular group there is a different pattern of such opaque spaces, said exposure means exposing successively and cyclically each of such rectangular groups of spaces, so that successive groups transmit energy from different combinations of portions of the whole area to the sensing means to cause the sensing means to produce a series of different electrical signals in accordance with the modulating effect of said mask, said signals representing the energy distribution over the area, and said optical means including means for spectrally analyzing the images transmitted by the non-opaque spaces.

2. Apparatus as claimed in claim 1, in which the first modulating mask has 2m-1 rows of 2p-1 spaces in each and said first exposure means exposes m X p of such spaces.

3. Apparatus as claimed in claim 1 including storage connected to the sensing means.

4. Apparatus as claimed in claim 1, having, following said first modulating mask and preceding said sensing means, means for analyzing for polarization of energy.

5. Apparatus as claimed in claim 1 wherein said means to expose said group comprises a framing mask for said first modulating mask and means for producing relative cyclical movement in two dimensions between said modulating mask and framing mask.

6. Apparatus as claimed in claim 5 having on the other side of said spectral analyzing means from said first modulating mask, a second modulating mask arranged in the same relative position and a second framing mask therefor, and means for producing relative cyclical movement between the second modulating mask and the second framing mask to scan each image from the first modulating mask and first framing mask, said second modulating mask having at least one row of spaces therein approximately one half of which are opaque and the remaining spaces non-opaque and said opaque spaces being so located that said second framing mask exposes in each position relative to the second framing mask a different pattern of opaque and non-opaque spaces.

7. Apparatus as claimed in claim 6, Having means for analyzing for polarization which includes a polarization analyzer, a quarter-wave plate and a birefringent plate, said birefringent plate being placed between the first and second modulating masks, said analyzer and quarterwave plate being turnable about the optical axis of the apparatus said birefringent plate, quarter-wave plate and polarization analyzer being removable from the light path singly or in combinations, said second modulating mask having an array of a plurality of rows of at least two spaces, and generally being approximately equal to the number m of rows of the first mask.

8. Apparatus for sequential production of a series of signals which series represents the value of electromagnetic radiation energy levels distributed over an area comprising means for imaging the area, energy sensing means for producing electrical signals in response to radiant energy incident thereupon, optical means between the imaging means and the sensing means for selectively transmitting energy from portions of the area to the sensing means including a first modulating mask with an array of a plurality of rows of at least two spaces in each, and a total of at least (2p-1)(2m-1) spaces where p and m are integers of substantial value such that the product p X m can represent the desired number of areal elements required for a predetermined accuracy of spatial resolution, means movable to expose a succession of rectangular groups, each group comprising a number of such spaces less than the total number thereof, approximately one-half of said spaces of said mask being opaque and the remaining spaces non-opaque, the opaque spaces being so located that in each exposed rectangular group there is a different pattern of such opaque spaces, said exposure means exposing successively and cyclically each of such rectangular groups of spaces, so that successive groups transmit energy from different combinations of portions of the whole area to the sensing means to cause the sensing means to produce a series of different electrical signals in accordance with the modulating effect of said mask, said signals representing the energy distribution over the area, said optical means including means for spectrally analyzing the images transmitted by the non-opaque spaces, said apparatus having on the other side of said spectral analyzing means from said first modulating mask, a second modulating mask, said second modulating mask having at least one row of spaces therein, approximately one half of such spaces of said second mask being opaque and the remaining spaces non-opaque, movable means associated with said second modulating mask to expose a succession of groups each of n spaces of the second mask where n is an integer of substantial value representing the desired number of spectral elements required for a predetermined degree of spectral resolution and there being at least 2n-1 of such spaces in said second modulating mask, the opaque spaces of the second modulating mask being so located that in each exposed group there is a different pattern of such opaque and non-opaque spaces, means for producing said succession of exposures of the second modulating mask in each position of the first modulating mask to scan the image modulated by the modulating mask, said sensing means comprising a single detector for receiving the images from said second modulating mask.

9. In an optical device for modulating radiation such as light from an extended object and sensing the energy in such a way as to obtain a series of signals from which both spatial resolution of different parts of the object and spectral resolution of the light coming from each part can be obtained, the device including a modulating mask, said mask having predetermined opaque and non-opaque spaces and combined with means to move it through a series of positions to produce radiations conforming thereto, spectral analyzing means for analyzing the Radiation modulated by said mask and a single detector responsive to detect the radiation passing from said analyzing means thereby to produce said series of signals, the improvement wherein said mask comprises a two dimensional pattern of opaque and non-opaque spaces, and means to expose sequentially a set of groups of said spaces, an individual group comprising opaque and non-opaque spaces distributed in both dimensions, said pattern and said means exposing a set of groups cooperatively related to deliver, to said detector, radiation modulated in accordance with a cyclic code, whereby, because radiation modulated by said mask and passing from said analyzing means in a given order can retain the effects of both, the signal output of said detector can contain in retrievable form spatial information represented by said two dimensional modulation as well as spectral information represented by the effects of said analyzing means, thereby enabling spatial resolution of light from said object in two dimensions with corresponding spectral resolution.

10. The optical device according to claim 9 wherein said analyzing means comprises a dispersion instrument and a second modulating mask receiving dispersed light from said dispersion instrument and a focusing means receives radiation from said second mask and directs it upon said single detector.

11. The optical device according to claim 10 wherein said second mask comprises a two dimensional pattern of opaque and non-opaque spaces, and means to expose sequentially a set of groups of said spaces, an individual group comprising opaque and non-opaque spaces distributed in both dimensions, said pattern and said means exposing a set of groups cooperatively related to deliver to said analyzing means radiation modulated in accordance with a cyclic code.

12. The optical device according to claim 11 wherein said means to expose said set of groups of spaces of said second mask is constructed to expose said set during exposure of each of said groups of said entrance mask.