463 research outputs found
Plug-and-Play Regularization on Magnitude with Deep Priors for 3D Near-Field MIMO Imaging
Near-field radar imaging systems are used in a wide range of applications
such as concealed weapon detection and medical diagnosis. In this paper, we
consider the problem of reconstructing the three-dimensional (3D)
complex-valued reflectivity distribution of the near-field scene by enforcing
regularization on its magnitude. We solve this inverse problem by using the
alternating direction method of multipliers (ADMM) framework. For this, we
provide a general expression for the proximal mapping associated with such
regularization functionals. This equivalently corresponds to the solution of a
complex-valued denoising problem which involves regularization on the
magnitude. By utilizing this expression, we develop a novel and efficient
plug-and-play (PnP) reconstruction method that consists of simple update steps.
Due to the success of data-adaptive deep priors in imaging, we also train a 3D
deep denoiser to exploit within the developed PnP framework. The effectiveness
of the developed approach is demonstrated for multiple-input multiple-output
(MIMO) imaging under various compressive and noisy observation scenarios using
both simulated and experimental data. The performance is also compared with the
commonly used direct inversion and sparsity-based reconstruction approaches.
The results demonstrate that the developed technique not only provides
state-of-the-art performance for 3D real-world targets, but also enables fast
computation. Our approach provides a unified general framework to effectively
handle arbitrary regularization on the magnitude of a complex-valued unknown
and is equally applicable to other radar image formation problems (including
SAR).Comment: 20 pages, 11 figures. The source codes and the dataset are made
available at
https://github.com/METU-SPACE-Lab/PnP-Regularization-on-Magnitud
Exact Relation Between Continuous and Discrete Linear Canonical Transforms
Abstract—Linear canonical transforms (LCTs) are a family of integral transforms with wide application in optical, acoustical, electromagnetic, and other wave propagation problems. The Fourier and fractional Fourier transforms are special cases of LCTs. We present the exact relation between continuous and discrete LCTs (which generalizes the corresponding relation for Fourier transforms), and also express it in terms of a new definition of the discrete LCT (DLCT), which is independent of the sampling interval. This provides the foundation for approximately computing the samples of the LCT of a continuous signal with the DLCT. The DLCT in this letter is analogous to the DFT and approximates the continuous LCT in the same sense that the DFT approximates the continuous Fourier transform. We also define the bicanonical width product which is a generalization of the time-bandwidth product. Index Terms—Bicanonical width product, fractional Fourier transform, linear canonical series, linear canonical transform
83 W, 3.1 MHz, square-shaped, 1 ns-pulsed all-fiber-integrated laser for micromachining
Cataloged from PDF version of article.We demonstrate an all-fiber-integrated laser based on off-the-shelf components producing square-shaped, 1 ns-long pulses at 1.03 mu m wavelength with 3.1 MHz repetition rate and 83 W of average power. The master-oscillator power-amplifier system is seeded by a fiber oscillator utilizing a nonlinear optical loop mirror and producing incompressible pulses. A simple technique is employed to demonstrate that the pulses indeed have a random chirp. We propose that the long pulse duration should result in more efficient material removal relative to picosecond pulses, while being short enough to minimize heat effects, relative to nanosecond pulses commonly used in micromachining. Micromachining of Ti surfaces using 0.1 ns, 1 ns and 100 ns pulses supports these expectations. (C) 2011 Optical Society of Americ
High-resolution Multi-spectral Imaging with Diffractive Lenses and Learned Reconstruction
Spectral imaging is a fundamental diagnostic technique with widespread
application. Conventional spectral imaging approaches have intrinsic
limitations on spatial and spectral resolutions due to the physical components
they rely on. To overcome these physical limitations, in this paper, we develop
a novel multi-spectral imaging modality that enables higher spatial and
spectral resolutions. In the developed computational imaging modality, we
exploit a diffractive lens, such as a photon sieve, for both dispersing and
focusing the optical field, and achieve measurement diversity by changing the
focusing behavior of this lens. Because the focal length of a diffractive lens
is wavelength-dependent, each measurement is a superposition of differently
blurred spectral components. To reconstruct the individual spectral images from
these superimposed and blurred measurements, model-based fast reconstruction
algorithms are developed with deep and analytical priors using alternating
minimization and unrolling. Finally, the effectiveness and performance of the
developed technique is illustrated for an application in astrophysical imaging
under various observation scenarios in the extreme ultraviolet (EUV) regime.
The results demonstrate that the technique provides not only
diffraction-limited high spatial resolution, as enabled by diffractive lenses,
but also the capability of resolving close-by spectral sources that would not
otherwise be possible with the existing techniques. This work enables high
resolution multi-spectral imaging with low cost designs for a variety of
applications and spectral regimes.Comment: accepted for publication in IEEE Transactions on Computational
Imaging, see DOI belo
Doping management for high-power fiber lasers: 100 W, few-picosecond pulse generation from an all-fiber-integrated amplifier
Cataloged from PDF version of article.Thermal effects, which limit the average power, can be minimized by using low-doped, longer gain fibers, whereas the presence of nonlinear effects requires use of high-doped, shorter fibers to maximize the peak power. We propose the use of varying doping levels along the gain fiber to circumvent these opposing requirements. By analogy to dispersion management and nonlinearity management, we refer to this scheme as doping management. As a practical first implementation, we report on the development of a fiber laser-amplifier system, the last stage of which has a hybrid gain fiber composed of high-doped and low-doped Yb fibers. The amplifier generates 100 W at 100 MHz with pulse energy of 1 mu J. The seed source is a passively mode-locked fiber oscillator operating in the all-normal-dispersion regime. The amplifier comprises three stages, which are all-fiber-integrated, delivering 13 ps pulses at full power. By optionally placing a grating compressor after the first stage amplifier, chirp of the seed pulses can be controlled, which allows an extra degree of freedom in the interplay between dispersion and self-phase modulation. This way, the laser delivers 4.5 ps pulses with similar to 200 kW peak power directly from fiber, without using external pulse compression. (C) 2012 Optical Society of Americ
Texturing of titanium (Ti6Al4V) medical implant surfaces with MHz-repetition-rate femtosecond and picosecond Yb-doped fiber lasers
Cataloged from PDF version of article.We propose and demonstrate the use of short pulsed fiber lasers in surface texturing using MHz-repetition-rate, microjoule- and sub-microjoule-energy pulses. Texturing of titanium-based (Ti6Al4V) dental implant surfaces is achieved using femtosecond, picosecond and (for comparison) nanosecond pulses with the aim of controlling attachment of human cells onto the surface. Femtosecond and picosecond pulses yield similar results in the creation of micron-scale textures with greatly reduced or no thermal heat effects, whereas nanosecond pulses result in strong thermal effects. Various surface textures are created with excellent uniformity and repeatability on a desired portion of the surface. The effects of the surface texturing on the attachment and proliferation of cells are characterized under cell culture conditions. Our data indicate that picosecond-pulsed laser modification can be utilized effectively in low-cost laser surface engineering of medical implants, where different areas on the surface can be made cell-attachment friendly or hostile through the use of different patterns. (C) 2011 Optical Society of Americ
83 W, 1 ns, 3.1 MHz all-fiber laser for micromachining
Fiber lasers are commonly used for various material processing applications. The advantages (such as simplicity of the system, high material removal rate) and disadvantages (larger heat-affected zone, reduced precision) of nanosecond pulses over sub-picosecond pulses are well known. © 2011 IEEE
Computational optical sensing and imaging 2021: feature issue introduction
This Feature Issue includes 2 reviews and 34 research articles that highlight recent works in the field of Computational Optical Sensing and Imaging. Many of the works were presented at the 2021 OSA Topical Meeting on Computational Optical Sensing and Imaging, held virtually from July 19 to July 23, 2021. Articles in the feature issue cover a broad scope of computational imaging topics, such as microscopy, 3D imaging, phase retrieval, non-line-of-sight imaging, imaging through scattering media, ghost imaging, compressed sensing, and applications with new types of sensors. Deep learning approaches for computational imaging and sensing are also a focus of this feature issue
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