US-12624991-B2 - Laser power detection using normalized linear slices to construct gaussian profiles

US12624991B2US 12624991 B2US12624991 B2US 12624991B2US-12624991-B2

Abstract

A system and method are provided for determining total laser power with photodiode sensors used to measure irradiance from the beam strike of the laser to identify linear offset Gaussian slices. The Gaussian for the slices is then solved to obtain a Gaussian profile, wherein solving to obtain the Gaussian profile includes: measuring an angle of incidence of a central axis of the laser beam relative to a normal axis of a plane containing the photodiode sensors; measuring a positional offset of the plane of the photodiode sensors relative to a plane perpendicular to the central axis of the laser beam; creating a projection of the plane of the photodiode sensors onto the plane perpendicular to a propagation of the beam to provide centered linear slices; and constructing the Gaussian profile from the centered linear slices. The total laser power is then determined from the Gaussian profile.

Inventors

Yong Jin Lee

Assignees

Fenix Research Corporation

Dates

Publication Date: 20260512
Application Date: 20240919

Claims (20)

1 . A method for determining total laser power for a laser, comprising: taking multiple spatial samples of a laser beam strike on a planar array of a plurality of detectors, each of the spatial samples received from a corresponding one of the detectors; measuring an irradiation profile of the laser beam strike for each of the multiple spatial samples of the laser beam strike to separately identify linear offset Gaussian slices for each of the multiple spatial samples; solving for a Gaussian of the irradiation profile to obtain a Gaussian profile of the laser beam, wherein solving to obtain the Gaussian profile comprises: measuring an angle of incidence of a central axis of the laser beam relative to a normal of plane the planar array; measuring a positional offset of the planar array relative to a plane perpendicular to the central axis of the laser beam; creating a projection of the plane in which the plurality of detectors located onto the plane perpendicular to the central axis of the laser beam using a linear transformation based on the positional offset and angle of incidence to provide normalized linear slices; and constructing the Gaussian profiles from the normalized linear slices; and determining the total laser power from the Gaussian profiles.
2 . The method of claim 1 , wherein the measuring the angle of incidence comprises: obtaining an array of diffraction spectral peaks from the laser beam strike; applying a transform to arrange the diffraction spectral peaks into a square grid of regularized peaks; using convolution kernels to determine a position of a central peak in the square grid of regularized peaks; and using a position of the central peak to calculate the angle of incidence of the axis of the laser beam relative to the spatial samples.
3 . The method of claim 2 , further comprising determining if the spatial samples are sensing light from a non-laser signal by determining if broad wavelength spectra are obtained from the multiple spatial samples.
4 . The method of claim 3 , further comprising determining if the spatial samples are sensing light from a non-laser by determining pulse rate and pulse width of light from the multiple spatial samples.
5 . The method of claim 1 , wherein the multiple spatial samples are measurements of irradiance, I, used to calculate the Gaussian profile wherein the irradiance I=I 0 exp[−2r 2 /w 2 ], with I being the beam irradiance measured at a point on the Gaussian profile determined using one of the spatial samples Io being peak beam irradiance which is an irradiance I at the center of the beam; w being beam radius which is a distance from the center of the beam to a position where power is reduced to 1/e 2 ; and r being a radius which is a distance from a center of the Gaussian to a measurement point.
6 . The method of claim 5 , wherein values for Io, w and r are determined for one of the linear offset Gaussian slices obtained from a pair of the spatial samples.
7 . The method of claim 6 , wherein further iterations are provided to refine the Gaussian profile by using additional spatial samples to provide additional linear offset Gaussian slices to determine the Gaussian profile.
8 . The method of claim 5 , further comprising: using the peak irradiation power Io to determine if an individual could have been exposed to maximum permissible exposure (MPE) of the laser.
9 . The method of claim 1 , wherein the total laser power is determined by taking an integral of the Gaussian profile.
10 . The method of claim 1 , further comprising: characterizing from parameters of the Gaussian profile beam divergence and magnification power from a beam expander of the laser.
11 . The method of claim 1 , further comprising determining if the multiple spatial samples are sensing light from a non-laser signal by spatially oversampling points when taking the multiple spatial samples and determining if the oversampled points correspond to a fitted Gaussian.
12 . An apparatus for determining total laser power of a laser comprising: a planar array of photodiode sensors configured to take multiple spatial samples of an irradiation profile from a beam strike of the laser to identify linear offset Gaussian slices for each of the multiple spatial samples used to solve for a Gaussian of the irradiation profile; a processor connected to the photodiode sensors, the processor configured to: measure an angle of incidence of a central axis of the laser beam relative to a normal of the planar array; measure a positional offset of the planar array relative to a plane perpendicular to the central axis of the laser beam; create a projection of the plane in which the photodiodes are located onto the plane perpendicular to the central axis of the laser beam using a linear transformation based on the positional offset and angle of incidence to provide linear slices; construct the Gaussian profiles from the normalized linear slices; and determine the total laser power from the Gaussian profiles.
13 . The apparatus of claim 12 , further comprising: a diffraction grating with sensors configured to provide an array of diffraction spectral peaks from the beam strike, wherein the diffraction grating provides an array of diffraction spectral peaks from the beam strike, and wherein the processor is connected to the diffraction grating with sensors and is further configured to: apply a transform to arrange the diffraction spectral peaks into a square grid of regularized peaks; use convolution kernels to determine a position of a central peak in the square grid of regularized peaks; and use a position of the central peak to calculate the angle of incidence of the axis of the laser beam relative to the diffraction grating.
14 . The apparatus of claim 13 , wherein the processor is further configured to determine if the spatial samples are sensing light from a non-laser signal by determining if broad wavelength spectra are received from the diffraction grating.
15 . The apparatus of claim 14 , wherein the processor is further configured to determine if the photodiode sensors are sensing light from a non-laser signal by spatially oversampling points using the photodiode sensors and determining if the oversampled points correspond to a fitted Gaussian.
16 . The apparatus of claim 12 , wherein the photodiodes are configured to provide measurements of irradiance I used to calculate the Gaussian profile, with I being a beam irradiance measured at a point on the Gaussian profile determined using one of the photodiodes, with the following additional parameters being determined for the Gaussian profile: peak beam irradiance Io which is an irradiance I at the center of the beam; beam radius w which is a distance from the center of the beam to a position where power is reduced to 1/e 2 ; and radius r which is a distance from a center of the Gaussian to a measurement point, and wherein values for Io, w and r are determined for one or more of the linear offset Gaussian slices obtained using a pair of the photodiodes.
17 . The apparatus of claim 12 , wherein the photodiode sensors are positioned on a square fixture and wherein the photodiode sensors include four sensors mounted at the corners of the square.
18 . The apparatus of claim 17 , wherein the photodiode sensors 8 sensors including the four photodiode sensors mounted at the four corners of the square and four photodiode sensors mounted along edges between the corners and further includes a 9 th sensor mounted near a center of the square.
19 . A non-transitory computer readable medium comprising stored instructions which when executed by a processor cause the processor to: measure an irradiation profile from a beam strike of laser by taking multiple spatial samples of the laser beam strike on a planar array of photosensors to identify linear offset Gaussian slices used to solve for a Gaussian of the irradiation profile; solve the Gaussian of the irradiation profile for each of the multiple spatial samples to obtain a Gaussian profile of the beam, wherein solving to obtain the Gaussian profile comprises: measure an angle of incidence of a central axis of the laser beam relative to a normal of the planar array; measure a positional offset of the planar array relative to a plane perpendicular to the central axis of the laser beam; create a projection of the plane in which the photodiodes are located onto the plane perpendicular to the central axis of the laser beam using a linear transformation based on the positional offset and angle of incidence to provide normalized linear slices; and construct the Gaussian profiles from the normalized linear slices; and determine the total laser power from the Gaussian profiles.
20 . The non-transitory computer readable medium of claim 19 , wherein the measuring the angle of incidence comprises: obtaining an array of diffraction spectral peaks from the laser beam strike; applying a transform to arrange the diffraction spectral peaks into a square grid of regularized peaks; using convolution kernels to determine a position of a central peak in the square grid of regularized peaks; and using a position of the central peak to calculate the angle of incidence of the axis of the laser beam relative to the spatial samples.

Description

CLAIM FOR PRIORITY This application claims priority to U.S. Provisional Application No. 63/625,468, filed on Jan. 26, 2024 and titled “Laser Power Detection” and U.S. Provisional Application No. 63/625,465, filed on Jan. 26, 2024 and titled “Laser Detector”, the contents of which are incorporated by reference herein in its entirety. FIELD Embodiments of the present technology generally relate to detection of a laser, and more specifically relate to detection of the power of the laser. BACKGROUND Laser detectors have been provided to determine when a laser is being used to target a vehicle, such as a laser used by police to determine if a vehicle is speeding. The laser detector notifies the user of the existence of such a laser source. Lasers have also been used to target pilots in aircraft. Such a laser beam strike can cause temporary or even permanent blindness of the pilot. Accurate and fast detection of such a laser using a laser detector that is provided in the aircraft to alert the pilot is desirable. It is desirable to determine characteristics of the laser source to determine if the laser is harmful to the pilot. It is also desirable to identify the location of the laser as quickly as possible to alert authorities to enable them to find the laser source and prevent further attempts to cause harm to pilots. Laser detectors can also be used to identify laser designators and optical range finders, allowing aircraft crew to take evasive action and address potential threats. SUMMARY Embodiments described herein provide a system and method for determining total power and maximum irradiance for a laser. The method first measures an irradiation profile from a beam strike of the laser by taking multiple spatial samples of the laser beam strike to identify linear offset Gaussian slices used to solve for a Gaussian of the irradiation profile. Next, the method solves the Gaussian of the irradiation profile to obtain a Gaussian profile of the beam, where solving to obtain the Gaussian profile includes the following steps: measuring an angle of incidence of a central axis of the laser beam relative to a normal axis of a plane containing the multiple spatial samples; measuring a positional offset of the plane containing the multiple spatial samples relative to a plane perpendicular to the central axis of the laser beam; creating a projection of the plane containing the multiple spatial samples onto the plane perpendicular to a propagation of the beam for the Gaussian profile using the positional offset to provide centered linear slices; and constructing the Gaussian profile from the centered linear slices using the angle of incidence. Total laser power is then determined by taking an integral of the centered Gaussian profile. Certain embodiments are provided for the step of measuring the angle of incidence which is done by obtaining an array of diffraction spectral peaks from photodiodes exposed to the laser beam strike. A transform is applied to arrange the diffraction spectral peaks into a square grid of regularized peaks. Convolution kernels are then used to determine the position of a central peak of the square grid of regularized peaks. The angle of incidence of the axis of the laser beam is then calculated using a position of the central peak. In the method embodiments, the multiple spatial samples are measurements of irradiance, I, used to calculate the Gaussian profile wherein the irradiance is I=I0 exp [−2r2/w2]. The value I is then the beam irradiance measured at a point on the Gaussian profile determined using one of the spatial samples. The value Io is the peak beam irradiance which is an irradiance I at the center of the beam. The value w is the beam radius which is a distance from the center of the beam to a position where power is reduced to 1/e2. The value r is a distance from a center of the Gaussian to a measurement point. Irradiance I can then be used to determine the total power P of the laser beam. In embodiments, the values for Io, w and r are determined for one of the linear offset Gaussian slices obtained from a pair of the photodiodes providing the spatial samples. In some embodiments, iterations are provided to refine the Gaussian profile by using additional pairs of the photodiodes providing spatial samples to provide additional linear offset Gaussian slices to determine the Gaussian profile. The peak irradiation power Io, or the highest value determined for Io is used to determine if a pilot or other individual could have been exposed to maximum permissible exposure (MPE) of the laser. Certain embodiments identify beams which are non-lasers so that only laser lights which can be harmful are evaluated. In an embodiment, it is determined if multiple spatial samples are sensing light from a non-laser signal by oversampling points when taking the multiple spatial samples and determining if the oversampled points correspond to a fitted Gaussian. In another embodiment, non-lasers are detected