This PDF file contains the front matter associated with SPIE Proceedings Volume 11135, including the Title Page, Copyright Information, Table of Contents, Author and Conference Committee lists.

Provided a coherently-illuminated extended object as well as a coherent point-source beacon, multiplexed digital holography grants both imaging and wavefront sensing functions for the purposes of atmospheric characterization. As such, this paper explores the tradespace between two multiplexed digital holography systems: one operating in the off-axis image plane recording geometry and the other operating in the off-axis pupil plane recording geometry. Via wave-optics simulations, we vary the signal-to-noise ratio and the sampling quotient for each recording geometry while assessing performance via several metrics including the field-estimated Strehl ratio. The performance for each recording geometry largely agrees with the theoretical results.

We present a numerical simulation of incoherent imaging of an extended object through distributed-volume atmospheric turbulence. As such, we can observe and quantify the effects of anisoplanitismin in the image plane of our optical system. Along with simulating the effects of anisoplantism, we aim to quantify the effects of polychromatic blurring in the image plane of our optical system. This outcome allows us to simulate the real-world scenario of a spectral filter with an effective bandpass. Using the spectral-slicing method, we define a square-response filter and discretely sample it at multiple wavelengths to simulate the polycromatic nature of our optical system. In turn, we find that the effects of polychromatic blurring are minimal, given modern-day narrowband filters. Thus, the use of monochromatic light is sufficient in simulating incoherent imaging; however, it is important to note that our results suggest that there may be a minor sampling error that would need to be addressed if the approach used here was to be expanded to an extremely broadband case.

This study investigates the use of a recently published extended generalized scaling law [Opt. Exp. 26(12), 15609-15622 (2018)]. In practice, the extended generalized scaling law accurately predicts the diffraction-limited peak irradiance in the far zone given the beam power, wavelength, propagation distance, field-effective area, and field-out-coupling factor. After reviewing this extended scaling law formulation, we compare the far-zone predictions for peak irradiance and Gaussian beam spread to wave-optics simulations which use the split-step beam propagation method and Monte-Carlo averaging. Compared to traditional approaches, the results show that this extended scaling law formulation does a better job in predicting the correct peak irradiance and the correct Gaussian beam spread for horizontal-path scenarios with varying levels of atmospheric turbulence.

In this study, we use a series of computational-wave-optics experiments to address the statistics associated with image-plane speckle fields resulting from a tilted flat plate that is rough compared to the wavelength of uniform illumination. To quantify the strength of simulated speckle, we make use of the focal ratio a.k.a. f number. This parameter provides a gauge for the size of speckles appearing across the image of a target. Our goal throughout is to show that, frame to frame, the analysis can appropriately simulate correlated speckle fields in an image plane. Our results show that the speckle fields we simulate are properly correlated from one frame to the next, relative to closed-form expressions. This outcome leads to the ability to perform closed-loop-tracking studies, which are becoming increasingly important for applications that involve imaging through turbulence.

Future adaptive optics systems will require advanced predictive control algorithms that mitigate loop latency by forecasting disturbances. In many applications, such as laser communications terminals, synthesizing such controllers is challenging due to the non-stationary nature of the disturbance statistics over long periods. We present initial experimental results using a new, multichannel, adaptive control algorithm applied on the Integrated Optical System, an extreme AO system under development for the Laser Communications Relay Demonstration. The adaptive controller implicitly tracks disturbance statistics, and provides broadband wavefront control without the need for open loop downtime. The results illustrate the improved disturbance rejection capabilities of the controller compared to a traditional integrator, even when the exogenous disturbance statistics evolve.

High-power laser systems are widely used for technological purposes or laser fusion experiments, but also to deliver the energy to some remote places here on the Earth as well as in space. Probably the only instrument to improve the phase structure of the laser beam is to use methods and elements of adaptive optics. The heart of any adaptive optical system is of course the deformable mirror. That is why the research and development of such optical elements continues for many years already. Here we propose a new stacked actuator mirror to be used to correct for not just the turbulent phase fluctuations, but also it should work with high CW power laser beams. Therefore, our mirror is a water-cooled one. Another important feature of this device is that each actuator could be easily substituted in case of failure. The mirror is 120 mm in diameter and has 121 control elements. Main characteristics of a mirror are presented in this work.

Bimorph deformable mirror with the clear aperture of 50 mm and 48 control electrodes and spatial light modulator with resolution of 1920x1080 pixels were used to increase the efficiency of focusing of partially coherent laser radiation, propagated through the 5 mm layer of the scattering suspension of 1 um polystyrene microspheres, diluted in distilled water, with the concentration values ranging from 10⁵ to 10⁶ mm-3. Medium with such parameters can be considered as an equivalent to the mid-dense fog layer with the length ranging from 300–500 meters up to 5 kilometers. Shack- Hartmann sensor was used to measure the distortions of averaged wavefront of laser beam, and CCD camera was used to estimate the intensity distribution of the focal spot in the far-field. Numerical and experimental investigation of the focusing improvement showed that it is possible to increase the peak intensity of the focal spot up to 45–60 %.

Digital-holographic detection provides a distinct way forward to combat the low signal-to-noise ratios (SNRs) associated with tactical applications. With that said, past efforts studied the major digital-holographic recording geometries used with tactical applications and derived closed-form expressions for their SNRs. They also used wave-optics simulations to validate the use of these closed-form expressions and found that for real-world scenarios, where we interfere a comparatively weak-signal beam with a strong-reference beam, the associated “weak-strong” expressions are accurate. For a laboratory setting, however, we often set the signal and reference beams to be nearly equal in power. As such, in this paper we derive closed-form expressions for this specific use case. We also use wave-optics simulations to explore the accuracy of these “equal-power” expressions. Overall, the results show that the equal-power expressions are accurate.

This paper makes use of digital-holographic detection in the off-axis image plane recording geometry to determine the Fried parameter of transmissive phase screens. Digital-holographic detection, in practice, provides us with an estimate of the complex-optical field (i.e., both the amplitude and wrapped phase); thus, we can use this estimate for determining the Fried parameter of transmissive phase screens, especially when the resulting aberrations follow Kolmogorov statistics. As such, this paper uses two experimental setups and Lexitek phase plates, which make use of Kolmogorov statistics to create aberrations with a prescribed Fried parameter. In both experimental setups, we place the Lexitek phase plates under test near the single-receiver lens of our digital-holographic system and assume isoplanatic conditions. In the first experimental setup, we uniformly illuminate a chrome-on-glass bar chart backed by Labsphere Spectralon®. We then use digital-holographic detection and an image-sharpening algorithm to indirectly measure the aberrations and determine the Fried parameter. In the second experimental setup, we send a collimated beam through the Lexitek phase plates. We then use digital-holographic detection to directly measure the aberrations and determine the Fried parameter. The results show that the first experimental setup overestimates the prescribed Fried parameter by 20%-60%, whereas the second experimental setup produces less variability with estimates of ±20% of the prescribed Fried parameter.

Digital holography (DH) has been demonstrated to be an effective wave-front sensor in low signal-to-noise ratio (SNR) environments due to the use of a strong reference. However, since DH relies on the interference of a signal with the mutually coherent reference, the coherence properties of the master-oscillator (MO) laser can degrade system SNR at long ranges. In this paper, a DH system in the off-axis image plane recording geometry was assembled and used to measure the effects of the MO coherence properties on the SNR. The coherence properties of the MO laser were degraded using sinusoidal phase modulation, which imparted maximum phase shifts of 0.38π, 0.55π, and 0.73π, at modulation frequencies of 20MHz to 100MHz. The measured coherence efficiency losses were closely predicted by the square of the fringe visibility, and deviated from the theoretical predictions by root-mean-squared errors of 0.0397, 0.0373, and 0.1007 for the three depths of modulation, respectively. The empirical data and models presented in this work may be used to assess efficiency losses in a DH system due to coherence effects.

This paper measures the mixing efficiency of a digital holography system at various optical path differences and hologram integrations times. From the measurements, the master oscillator (MO) laser spectral lineshape and linewidth is estimated. The lineshape was Gaussian, which is indicative of laser frequency flicker noise or 1/f noise, and the linewidth decreased by 65% when the integration time was decreased from 100 ms to 0.1 ms. This reduction in the observed MO laser linewidth yields an increased coherence length and time of 280%. A flicker noise model for the linewidth and integration time is used and approximates the measurements to within 17%.

There are many approaches to incoherent imaging through the atmosphere that involve joint estimation of multiple turbulence-induced wavefront-aberration realizations and an object that is common across realizations. These approaches, all of which use short-exposure or “speckle” data, include Multi-Frame Blind Deconvolution (MFBD), Phase-Diverse Speckle (PDS), and Wavelength-Diverse Speckle (WDS). We enumerate fundamental estimation ambiguities that arise within each of these modalities and identify strategies to eliminate some of the ambiguities.

A hyper-Laplacian can model the heavy-tailed distribution of gradients in natural scenes well, which have proven effective priors for deconvolution and denoising. However, because of missing point spread function (PSF) information in the two-dimensional spatial domain of optical sparse aperture (OSA) systems, a hyper-Laplacian prior of single exposure cannot recover the missing information of images. The main focus of this paper is on combining hyper-Laplacian priors with a pupil and its rotated pupils to compensate PSF information and improve the image quality in OSA systems. A scheme of rotating the pupil that has double apertures is analyzed. The cost function relative to multiple degraded images and PSFs obtained by rotating the pupil is established. The alternating minimization algorithm consisting of two phases is implemented to acquire restored images. In one phase, the non-convex part of the problem is solved. In the other phase, the fast Fourier transforms (FFTs) are used to solve a quadratic equation in the frequency domain. Using the peak signal-to noise ratio (PSNR), a quantitative analysis is provided. Simulation results show that hyper-Laplacian priors combined with rotating pupils can restore images better than a hyper-Laplacian prior of single exposure in an OSA system. Taking spoke-square image as the test image, the PSNR is 28.34 dB with two rotations and 23.52 dB without rotation. Moreover, the numbers of rotating the pupil that lead to different changes of the image quality are demonstrated.

The nascent field of indirect imaging is concerned with the recovery of information pertaining to objects that are beyond the line-of-sight (LoS) and hidden from view. Current approaches to indirect imaging are either limited in their ability to recover spatially resolved imagery (resolution of few centimeters at 1-meter standoff) or impose severe restrictions on the imaging geometry. The present work examines two approaches that recover spatial detail on hidden objects by exploiting spatial and spectral correlation in the light scattered by the objects. Experiments have demonstrated the ability to discern sub-millimeter spatial detail, on centimeter sized objects positioned 1-meter behind a wall.

Phase-space tomography describes the recovery of signals from a tomographic reconstruction of the generalized radiance distribution with measurements being interpreted as projections of phase space. For coherent signals the phase space of the Wigner distribution function is a highly redundant signal representation. For efficient signal recovery based on phase-space information, it is necessary to address these redundancies. To understand the number of independent measurements necessary for the recovery of the WDF, Talbot self-imaging is used to derive a formalism for discrete phase-space tomography and signal recovery.

We recover the shape and orientation of an object by analyzing the spatial phase and amplitude of a transmitted optical beam using a single pixel. We experimentally demonstrate using the complex spatial spectrum of multiple sequential measurements of a varying probe beam. Specifically, we transmit a structured beam that is tailored to have one mode of the Laguerre-Gaussian (LG) modal basis set, and the beam is varied to sequentially have a unique azimuthal (l) and radial (p) value. When each uniquely structured beam probes an object, there will be coupling of power from the pure mode to other LG modes. The complex phase and amplitude coefficients of this modal power coupling will provide a “signature” of the probed object’s 2D structure, and this signature can be detected using a single pixel. We identify a “fan-shaped” object with an opening angle of 120˚ and different angular orientations by analyzing the corresponding complex spatial spectrum of multiple sequential measurements, such that each subsequent tailored mode has l and p indices in the range -15 - +15 and 0-30, respectively. Results show that the amplitude spectrum is insensitive to the object’s angular orientation, whereas the phase spectrum predictably shifts with orientation. Additionally, we demonstrate that an irregular image with a ‘SC’ logo can be reconstructed using the complex modal spectrum. The structural similarity (SSIM) of the reconstructed image increases as the number of modes increases. Specifically, the SSIM increases by 83.5% when the number of modes increases from 36 (6 by 6) to 961 (31 by 31).

For small satellite remote sensing missions, a large aperture telescope which has more than 400 mm of diameter is required to realize less than 1m GSD observations. However, it is difficult or expensive to realize the large aperture telescope using monolithic primary mirror with high surface accuracy. Generally, not only high accuracy of optical surface but also high accuracy of optical alignment is required for large aperture telescope. For a segmented mirror telescope, aligning optical elements in high accuracy is more difficult and more important. For conventional systems, optical alignment is adjusted before launch to achieve desired imaging performance. However, it is difficult to adjust the alignment for large sized optics in high accuracy. Furthermore, thermal environment in orbit and vibration in launch vehicle cause the misalignments of the optics. We are developing an adaptive optics system using a MEMS deformable mirror (DM) for Earth observing remote sensing sensor. Image based adaptive optics system compensate the misalignments and wavefront aberration of optical elements using DM by feedback of observed images. Because, it is difficult to use a reference point source unless the satellite controls its attitude toward a star for Earth observing systems. Furthermore, total amount of incident light can enter an image sensor.

We propose the control algorithm of DM and mirror segments for a segmented mirror telescope by using of observed images. Numerical simulation results represent that misalignment and wavefront aberration of the segmented mirror telescope are corrected and image quality is improved.