We present a graded index (GRIN) design methodology for application in coherent beam shaping with... more We present a graded index (GRIN) design methodology for application in coherent beam shaping within the confines of geometric optics. In theory, a GRIN structure can be designed to convert a specific but arbitrary incident wave into any general amplitude and phase distribution. The incident and the desired output waves are converted into ray distributions where the local ray density is associated with the field amplitude and the ray direction and its optical path length are associated with the phase front of the waves. A set of ray paths is chosen to achieve the conversion between the initial and final ray distributions. Intermediate wavefronts are extrapolated from the ray paths and used to determine the refractive index profile required to effect the gradual evolution of the wave as it propagates through the structure. Our method is demonstrated by a GRIN structure design that converts a Gaussian beam into a flattop beam. In addition, several techniques used to reduce the dynamic range of the refractive index in the structure are examined and a design recipe is developed for this particular application. A ray trace shows that the resulting structure achieves the desired remapping of rays and produces a flat-top beam from an incident Gaussian beam.
We present a numerical method for retrieving the refractive index distribution in two-dimensional... more We present a numerical method for retrieving the refractive index distribution in two-dimensional gradient-index media from external measurements of laser beam deflection. Using an iterative approach to ascertain the boundary positions and angles of probe beams that transit the optical medium and constructing approximate beam trajectories that satisfy these boundary values, we show that the inverse problem can be reduced to the inversion of a sparse linear algebraic system. The beam trajectories are subsequently corrected using an iterative ray trace procedure that continually refines the computed solution and the associated boundary values. We demonstrate our method in simulation by calculating the refractive index distribution of a hypothetical 2-D gradient-index element from computer-generated external beam deflection data, where RMS index errors below 1% of the index range (nmax − nmin) are achieved.
Journal of the Optical Society of America, Jul 8, 2021
We present a method for recovering the perspective image of a non-line-of-sight scene based on pl... more We present a method for recovering the perspective image of a non-line-of-sight scene based on plenoptic observations of indirect photons scattered from a flat homogeneous surface. The plenoptic information is used to ascertain locations of non-line-of-sight features in a hidden scene. This latent knowledge is then used for the partial reconstruction of the scene by extracting the imagery perceived by the non-line-of-sight features from the scattered light field measured along the surface. We demonstrate the efficacy of our technique by applying it to synthetic and measured light field data to retrieve the locations of multiple knife-edge occlusions in a test scene along with their perceived imagery.
Journal of the Optical Society of America, Jun 25, 2021
The scattered light distribution of surfaces in the long-wave infrared (λ∼8−12µm) is measured usi... more The scattered light distribution of surfaces in the long-wave infrared (λ∼8−12µm) is measured using a small set of thermal camera images. This method can extract scatter patterns considerably faster than standard laboratory bidirectional reflectance distribution function measurements and is appropriate for passive homogeneous surfaces. Specifically, six images are used in this study, each taken with respect to a thermal light source at an angle ranging from 10° to 60° to the normal of the surface. This data is deconvolved with the shape of the light source to estimate the scattering pattern. Both highly specular (black Masonite) and diffuse (painted drywall) surfaces are tested. Errors between the estimated scattering distribution and a directly measured one using a goniometer stage and quantum-cascade laser (QCL) are less than or equal to 3% except for extremely specular surfaces where viable QCL measurements cannot be made due to the increased relative contribution of speckle noise.
We present a passive technique for recovering the conventional imagery of a non-line- of-sight sc... more We present a passive technique for recovering the conventional imagery of a non-line- of-sight scene using the spatial and angular components of the scattered light field along a homogeneous surface.
The frequency locking range of a laser diode array was experimentally determined. A one-dimension... more The frequency locking range of a laser diode array was experimentally determined. A one-dimensional array of seven lasers was phase-locked by placing it in an external optical cavity to establish coupling between the lasers. It was found that the experimental frequency locking range was four times greater than the theoretical locking range. The large experimental locking range demonstrates that there appears to be a greater tolerance of path-length errors in phase-locked laser arrays than the theory had earlier implied.
Journal of the Optical Society of America, Mar 11, 2020
We present a methodology for recovering the perspective imagery of a non-line-of-sight scene base... more We present a methodology for recovering the perspective imagery of a non-line-of-sight scene based on plenoptic observations of indirect photons scattered from a homogeneous surface. Our framework segregates the visual contents observed along the scattering surface into angular and spatial components. Given the reflectance characteristics of the scatterer, we show that the former can be deduced from scattering measurements employing diversity in angle at individual surface points, whereas the latter can be deduced from captured images of the scatterer based on prior knowledge of occlusions within the scene. We then combine the visual contents from both components into a plenoptic modality capable of imaging at higher resolutions than what is allowed by the angular information content and discriminating against extraneous signals in complex scenes that spatial information struggles to discern. We demonstrate the efficacy of this approach by reconstructing the imagery of test scenes from both synthetic and measured data.
We present a passive, non-line-of-sight imaging technique where we use the scattered light field ... more We present a passive, non-line-of-sight imaging technique where we use the scattered light field along a surface to discover hidden occluding features in the scene and utilize the plenoptic information for scene reconstruction.
ABSTRACT Q-switching in a Yb-doped fiber laser is quenched by providing an alternative lasing wav... more ABSTRACT Q-switching in a Yb-doped fiber laser is quenched by providing an alternative lasing wavelength to prevent inversion build-up. 98 % of the non Q-switched power is preserved while completely eliminating the Q-switched pulse.
We present a graded index (GRIN) design methodology for application in coherent beam shaping with... more We present a graded index (GRIN) design methodology for application in coherent beam shaping within the confines of geometric optics. In theory, a GRIN structure can be designed to convert a specific but arbitrary incident wave into any general amplitude and phase distribution. The incident and the desired output waves are converted into ray distributions where the local ray density is associated with the field amplitude and the ray direction and its optical path length are associated with the phase front of the waves. A set of ray paths is chosen to achieve the conversion between the initial and final ray distributions. Intermediate wavefronts are extrapolated from the ray paths and used to determine the refractive index profile required to effect the gradual evolution of the wave as it propagates through the structure. Our method is demonstrated by a GRIN structure design that converts a Gaussian beam into a flattop beam. In addition, several techniques used to reduce the dynamic range of the refractive index in the structure are examined and a design recipe is developed for this particular application. A ray trace shows that the resulting structure achieves the desired remapping of rays and produces a flat-top beam from an incident Gaussian beam.
We present a numerical method for retrieving the refractive index distribution in two-dimensional... more We present a numerical method for retrieving the refractive index distribution in two-dimensional gradient-index media from external measurements of laser beam deflection. Using an iterative approach to ascertain the boundary positions and angles of probe beams that transit the optical medium and constructing approximate beam trajectories that satisfy these boundary values, we show that the inverse problem can be reduced to the inversion of a sparse linear algebraic system. The beam trajectories are subsequently corrected using an iterative ray trace procedure that continually refines the computed solution and the associated boundary values. We demonstrate our method in simulation by calculating the refractive index distribution of a hypothetical 2-D gradient-index element from computer-generated external beam deflection data, where RMS index errors below 1% of the index range (nmax − nmin) are achieved.
Journal of the Optical Society of America, Jul 8, 2021
We present a method for recovering the perspective image of a non-line-of-sight scene based on pl... more We present a method for recovering the perspective image of a non-line-of-sight scene based on plenoptic observations of indirect photons scattered from a flat homogeneous surface. The plenoptic information is used to ascertain locations of non-line-of-sight features in a hidden scene. This latent knowledge is then used for the partial reconstruction of the scene by extracting the imagery perceived by the non-line-of-sight features from the scattered light field measured along the surface. We demonstrate the efficacy of our technique by applying it to synthetic and measured light field data to retrieve the locations of multiple knife-edge occlusions in a test scene along with their perceived imagery.
Journal of the Optical Society of America, Jun 25, 2021
The scattered light distribution of surfaces in the long-wave infrared (λ∼8−12µm) is measured usi... more The scattered light distribution of surfaces in the long-wave infrared (λ∼8−12µm) is measured using a small set of thermal camera images. This method can extract scatter patterns considerably faster than standard laboratory bidirectional reflectance distribution function measurements and is appropriate for passive homogeneous surfaces. Specifically, six images are used in this study, each taken with respect to a thermal light source at an angle ranging from 10° to 60° to the normal of the surface. This data is deconvolved with the shape of the light source to estimate the scattering pattern. Both highly specular (black Masonite) and diffuse (painted drywall) surfaces are tested. Errors between the estimated scattering distribution and a directly measured one using a goniometer stage and quantum-cascade laser (QCL) are less than or equal to 3% except for extremely specular surfaces where viable QCL measurements cannot be made due to the increased relative contribution of speckle noise.
We present a passive technique for recovering the conventional imagery of a non-line- of-sight sc... more We present a passive technique for recovering the conventional imagery of a non-line- of-sight scene using the spatial and angular components of the scattered light field along a homogeneous surface.
The frequency locking range of a laser diode array was experimentally determined. A one-dimension... more The frequency locking range of a laser diode array was experimentally determined. A one-dimensional array of seven lasers was phase-locked by placing it in an external optical cavity to establish coupling between the lasers. It was found that the experimental frequency locking range was four times greater than the theoretical locking range. The large experimental locking range demonstrates that there appears to be a greater tolerance of path-length errors in phase-locked laser arrays than the theory had earlier implied.
Journal of the Optical Society of America, Mar 11, 2020
We present a methodology for recovering the perspective imagery of a non-line-of-sight scene base... more We present a methodology for recovering the perspective imagery of a non-line-of-sight scene based on plenoptic observations of indirect photons scattered from a homogeneous surface. Our framework segregates the visual contents observed along the scattering surface into angular and spatial components. Given the reflectance characteristics of the scatterer, we show that the former can be deduced from scattering measurements employing diversity in angle at individual surface points, whereas the latter can be deduced from captured images of the scatterer based on prior knowledge of occlusions within the scene. We then combine the visual contents from both components into a plenoptic modality capable of imaging at higher resolutions than what is allowed by the angular information content and discriminating against extraneous signals in complex scenes that spatial information struggles to discern. We demonstrate the efficacy of this approach by reconstructing the imagery of test scenes from both synthetic and measured data.
We present a passive, non-line-of-sight imaging technique where we use the scattered light field ... more We present a passive, non-line-of-sight imaging technique where we use the scattered light field along a surface to discover hidden occluding features in the scene and utilize the plenoptic information for scene reconstruction.
ABSTRACT Q-switching in a Yb-doped fiber laser is quenched by providing an alternative lasing wav... more ABSTRACT Q-switching in a Yb-doped fiber laser is quenched by providing an alternative lasing wavelength to prevent inversion build-up. 98 % of the non Q-switched power is preserved while completely eliminating the Q-switched pulse.
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Papers by James Leger