Laser detector
A system and method are provided for characterizing a laser using a diffraction grating. The system includes a lens that projects diffraction patterns from the diffraction grating as an image of diffraction peaks onto a plane. Optical sensors then sense the diffraction peaks. A processor connected to the optical sensors applies the laser characterization method to determine the laser wavelength, irradiance and angle of incidence. In the method, the processor obtains the diffraction peak measurements from the optical sensors and applies a transform to arrange the diffraction peaks into a grid of regularly spaced peaks. The processor then applies convolution kernels to analyze the grid of regularized peaks to determine a wavelength, irradiance and angle of incidence of the laser.
1 . A method for characterizing a laser comprising:
obtaining an array of diffraction peaks from a laser beam strike on a diffraction grating;
using an optical lens to project the array of diffraction peaks as an image;
sensing the diffraction peaks from the image by optical sensors;
applying a transform to the image to arrange the diffraction peaks into a grid of regularly spaced peaks;
performing a cross-correlation of a plurality of convolution kernels with the grid of regularly spaced peaks, each of the plurality of convolution kernels having a different pitch;
analyzing the cross-correlation of the plurality of the convolution kernels to determine a wavelength of the laser beam; and
analyzing the cross-correlation of the plurality of the convolution kernels to determine the irradiance of the laser beam from intensity profiles of the grid of regularly spaced peak.
2 . The method of claim 1 , wherein:
the grid of regularly spaced peaks comprises a square grid of peaks;
analyzing the cross-correlation of the plurality of the convolution kernels to determine the irradiance of the laser beam comprises determining a distance between peaks of the square grid of peaks wherein the distance between peaks is used to determine the wavelength of the laser beam; and
analyzing the cross-correlation of the plurality of the convolution kernels to determine the irradiance of the laser beam comprises determining an intensity profile of the square grid of peaks wherein the intensity profile of the peaks is used to determine the irradiance of the laser.
3 . The method of claim 1 , wherein the grid of regularized peaks comprises a distinct pattern of peaks that is analyzed by the convolution kernels to determine the wavelength by spatially filtering the image then applying a series of two-dimensional Shah fuctions.
4 . The method of claim 1 , wherein:
the laser wavelength is determined by convolving a series of kernels corresponding to a pitch of the regularized peaks and evaluating a resulting convolved image to determine a kernel that produced a best fit with the grid of regularized peaks.
5 . The method of claim 1 , wherein
the optical sensors comprise primary sensors and secondary sensors, wherein the primary sensors have a higher signal reception resolution than the secondary sensors, wherein the laser beam is characterized by performing analysis on a sequence of progressively higher resolution images starting with screening signals detected by the secondary sensors, and
using convolution kernels optimized for each of the sequences of images, using initial ones of the convolution kernels to determine if initial ones of the grids have a pattern of regularized peaks that are of high enough resolution to identify the laser and using subsequent ones of the convolution kernels to determine a higher resolution distance between peaks of the grids of regularized peaks to identify the wavelength for the laser.
6 . The method of claim 1 , wherein:
the array of diffraction peaks include distinct patterns with varying pitches when multiple lasers are present corresponding to a specific wavelengths corresponding to the multiple lasers that is detectable by the convolution kernels,
the convolution kernel determines the wavelength of the laser beam as well as a wavelength of additional ones of the multiple lasers within the specific wavelengths, and
the convolution kernel further determines the irradiance for each wavelength from the intensity profile of the peaks corresponding to each wavelength.
7 . The method of claim 1 , including image based processing that comprises:
processing the image to highlight patterns of the regularly spaced diffraction peaks characteristic of a laser and to suppress regions from a non laser source which do not have well defined diffraction peaks.
8 . The method of claim 1 , wherein for situations where centrally located ones of the diffraction peaks are saturated:
the wavelength is computed by obtaining a pitch of higher order ones of the diffraction peaks that are not saturated, and
the intensity profiles for the saturated centrally located peaks are computed from a measurement of peripheral ones of the diffraction peaks and by applying diffraction theory that defines an envelope for the diffraction peaks.
9 . The method of claim 1 , wherein when saturation of regions of the diffraction peaks is detected:
the convolution kernels are optimized to determine ones of the intensity profiles of the diffraction peaks in an unsaturated region of the image plane and to obtain an estimate of ones of the intensity profiles of the diffraction peaks in the saturated region based on the unsaturated ones of the diffraction peaks, and
the intensity profiles are used to compute the irradiance of the laser.
10 . The method of claim 1 , wherein:
the array of diffraction peaks is a two dimensional array of diffraction peaks that are converted to horizontal and vertical one-dimensional signals; and
the convolution kernel processes the signals resulting from at least one of the horizontal and vertical one-dimensional signals to determine spacing between peaks to identify wavelength and amplitudes of the peaks to determine the irradiance.
11 . The method of claim 10 , wherein the laser is characterized by regularly spaced peaks in at least one of the one dimensional signals and the expected intensities of the peaks of the orders of the diffraction.
12 . The method of claim 10 , wherein the convolution kernel identifies peaks that match the expected pitch and intensities of the diffraction peaks created by the laser.
13 . The method of claim 10 , wherein:
the horizontal one dimensional signals constitute row signals and the vertical one dimensional signals constitute column signals; and
the convolution kernel processes the row signals and column signals to determine spacing between peaks by using a summation of the intensities in the rectilinearized diffraction image.
14 . An apparatus for characterizing a laser comprising:
a diffraction grating for receiving a laser beam strike;
a lens that projects diffraction patterns from the diffraction grating as an image of diffraction peaks onto a plane;
optical sensors for sensing diffraction peaks from the image output from the diffraction grating resulting from the laser beam strike;
a processor connected to the optical sensors, the processor being configured to:
obtain the array of diffraction peaks from the laser beam strike;
apply a transform to arrange the diffraction peaks into a grid of regularly spaced peaks;
performing a cross-correlation of a plurality of convolution kernels with the grid of regularly spaced peaks, each of the plurality of convolution kernels having a different pitch;
analyzing the cross-correlation of the plurality of the convolution kernels to determine a wavelength of the laser beam; and
analyzing the cross-correlation of the plurality of the convolution kernels to determine the irradiance of the detected laser beam from intensity profiles of the grid of regularly spaced peaks.
15 . The apparatus of claim 14 , wherein the imaging lens is an orthographic projection lens that follows the sine law that natively generates diffraction peaks in a square grid.
16 . The apparatus of claim 14 , wherein the optical sensors comprise:
secondary sensors for screening signals received from the optical sensors to identify the laser beam relative to non-lasers; and
primary sensors with higher power consumption and higher resolution than the secondary sensors for use by the convolution kernels to determine the wavelength of the laser beam.
17 . The apparatus of claim 14 , wherein the optical lens comprises a first optical lens group as well as a second optical lens group, wherein the diffraction grating is placed between the first and the second optical lens groups forming a lens assembly.
18 . The apparatus of claim 14 , wherein the diffraction grating comprises an optical element with two dimensional features designed to create specific diffraction patterns.
19 . The apparatus of claim 14 , wherein the diffraction grating comprises a combination of two or more linear diffraction gratings placed at specific angles with respect to each other.
20 . The apparatus of claim 19 , wherein the combination of two or more linear diffraction gratings comprise two diffraction gratings and the specific angles are 90 degrees with respect to each other.
21 . The apparatus of claim 19 , wherein the combination of two or more linear diffraction gratings comprise three diffraction gratings and the specific angles are 60 degrees with respect to each other.
22 . The apparatus of claim 14 , wherein the diffraction grating is configured to rotate.