For wavefront sensing and control, the most extensive use of Mult-Conjugate Adaptive Optics (MCAO) systems for extended-path aberration compensation lies with the use of multiple Laser Guide Stars (LGS) for Multi-Conjugate Adaptive Optics (MCAO). Ground-based adaptive optics systems were initially developed by the Starfire Optical Range (SOR) in 1983. Both Rayleigh guide stars and Na guide stars have been developed. More recently, both laser systems, Na LGS at 93 km and Rayleigh guide stars at 20 km, are being combined in the Large Binocular Telescope (LBT) for multiple LGS for Multiple Conjugate Adaptive Optics (MCAO) (M. Hart et al, 2011). Each side of the LBT has 3 Rayleigh LGS which are projected into two triangular constellations. A sodium LGS will be added to each aperture using the same launch optics as the Rayleigh beacons. This will combine low altitude Rayleigh LGS and high altitude Na laser guide stars into a uniquely powerful tomographic wavefront sensing system for Multi-Conjugate Adaptive Optics. Other observatories have used either Rayleigh guide stars or Na guide stars. ESO VLT has 4 Na LGS. MMT has 5 Rayleigh guide stars. Gemini Multi-Conjugate Adaptive Optics System (GEMS) has 5 Na LGS. The many multiple LGS MCAO observatories will be compared for effective design and projected performance.

Branch points form from interference within a propagating wave due to phase differences imparted by atmospheric turbulence. In the companion paper, we demonstrated that the characteristics of density and separation found in our experimental work are reproducible in an independent wave optical simulation. In this paper, we expand on this demonstration to include the measurement of the number and velocities of branch point producing turbulence layers as well as the existence of persistent pairs in pupil plane measurements. Together these two papers verify our previous experimental results on pupil plane branch point measurements.

Previous theoretical work, to first order, demonstrated that branch points are markers for photons carrying orbital angular momentum (OAM), but gave to indication of the flux associated with a given branch point distribution. In a parallel effort, the OAM flux as a ratio of the total flux is calculated, but that work relies on knowing the non-zero elements in the slope discrepancy Hilbert space. Here, we calculate the “size” of the slope discrepancy Hilbert space for our previously published data.

With an optical phased array, the individual phases of a multi-fiber laser source can be manipulated by exploiting high-bandwidth phase loops to correct for aero-optical flow over the turret and free-stream atmospheric effects along the line of sight; however, rough surface scatter through laser-target interaction adds the additional constraints of speckle and depolarizing effects. In particular, speckle phenomena can cause unobservable modes to arise in the beam control system of optical phased arrays. One such unobservable mode is termed stair mode and is appropriately identified by a stair-step pattern of piston phase across the individual subapertures that comprise a tiled aperture. This paper investigates the effects of stair mode using wave-optics simulations. To represent different array fill factors in the source plane, both seven and 19 element hexagonal close-packed tiled apertures are used in the simulations along with both Gaussian and flat-top outgoing beamlets. Peak Strehl ratio and power in the bucket are calculated in the target plane for all simulation setups and are then averaged for multiple random realizations of stair mode step sizes. In addition, the stair mode target irradiance patterns are imaged with cameras which have decreasing aperture stop diameters. Initial results show that low resolution imaging conditions, i.e. an aperture stop on the order of a subaperture diameter, makes it difficult to distinguish between different realizations of stair mode using a separate camera sensor.

A novel and memory efficient method for computing diffraction patterns produced on large-scale focal planes by largescale Coded Apertures at wavelengths where diffraction effects are significant has been developed and tested. The scheme, readily implementable on portable computers, overcomes the memory limitations of present state-of-the-art simulation codes such as Zemax. The method consists of first calculating a set of reference complex field (amplitude and phase) patterns on the focal plane produced by a single (reference) central hole, extending to twice the focal plane array size, with one such pattern for each Line-of-Sight (LOS) direction and wavelength in the scene, and with the pattern amplitude corresponding to the square-root of the spectral irradiance from each such LOS direction in the scene at selected wavelengths. Next the set of reference patterns is transformed to generate pattern sets for other holes. The transformation consists of a translational pattern shift corresponding to each hole’s position offset and an electrical phase shift corresponding to each hole’s position offset and incoming radiance’s direction and wavelength. The set of complex patterns for each direction and wavelength is then summed coherently and squared for each detector to yield a set of power patterns unique for each direction and wavelength. Finally the set of power patterns is summed to produce the full waveband diffraction pattern from the scene. With this tool researchers can now efficiently simulate diffraction patterns produced from scenes by large-scale Coded Apertures onto large-scale focal plane arrays to support the development and optimization of coded aperture masks and image reconstruction algorithms.

One obstacle to optimizing performance of large-scale coded aperture systems operating in the diffractive regime has been the lack of a robust, rapid, and efficient method for generating diffraction patterns that are projected by the system onto the focal plane. We report on the use of the 'Shrekenhamer Transform' for a systematic investigation of various types of coded aperture designs operating in the diffractive mode. Each design is evaluated in terms of its autocorrelation function for potential use in future imaging applications. The motivation of our study is to gain insight into more efficient optimization methods of image reconstruction algorithms.

We take in consideration three applications which are strongly affected from atmospheric as well as artificial turbulence. Systems in development at the IOSB institute for correcting the turbulence in each application are reported. The set of problems we are interested in are related to the tracking of objects through the atmosphere, the improvement of a laser beam for laser communication or countermeasure and the imaging of objects distorted from turbulent layers. We propose the use of adaptive optics (AO) based on classical Shack-Hartmann sensors (SH) to improve the performances of tracking systems. The SH has the advantage to be sufficiently fast, robust and suited for coherent as well as incoherent point sources correction. In consequence it is also well suited for the purpose of laser beam correction in the atmosphere. The problem of improving a complex image or scene cannot be solved with wavefront sensors in an easy way. A correction of the wavefront based on quality metric estimation and the Stochastic Parallel Gradient Descent (SPGD) algorithm is then reported here to cover this aspect. In the final part two modifications of the SPGD algorithm to improve its performances are proposed.

Laser aided detection and ranging (LADAR) imaging systems are usually corrupted by several pathologic noises. Speckle noise is due to the coherent nature of the laser illuminator. Scintillation noise is introduced by atmospheric turbulence over the outgoing illumination path and manifests itself as a multiplicative noise in the imagery. These noises can be mitigated by a simple recursive averaging algorithm when looking at fixed targets in staring mode. However if the target under observation is moving with respect to the imaging platform, the averaging will cause the target image to smear. In such a case, a maximum a-posteriori (MAP) approach can be used to estimate localized statistics of the scene under observation as well as the scintillation. The parameter estimates can then be incorporated into a spatially and temporally adaptive averaging approach which mitigates the noise while at the same time preserving motion in the scene.

3D imaging LADAR Avalanche Photo-Diode (APD) arrays are emerging as an important technology for future generation remote sensing and reconnaissance systems. One important limiting factor in their development is the pixel pitch, which is typically 100 micrometers. This makes the spatial resolution of an APD array at least 10 times lower than their Charge Coupled Device (CCD) array counterparts. With the development of smaller pixel-pitch APD arrays in 3D applications that rival those of CCD’s used in 2D imaging many years away, this research endeavors to fuse 3D images with poor spatial resolution with 2D images to obtain superior spatial and range resolution. Microscanning or dithering is a technique used to combine multiple images of the same scene to obtain a more densely sampled version. This techniques has been applied successfully to both 2D and 3D imagery. In this paper, a standard microscanning approach is compared to a new technique involving the use of a properly sampled 2D image combined with multiple low-resolution 3D images in order to obtain a more densely sample 3D image. The comparison will report the mean squared range error obtained from the traditional microscanning approach and the new 2D/3D fusion approach as a function of the number of 3D frames used in the image reconstruction. Since the 2D image contains no range information, improvements in mean squared range error by the new algorithm demonstrate its ability to successfully fuse 2D add 3D information.

Laser Aided Detection and Ranging (LADAR) imaging systems can be used to provide high resolution imaging and tracking of moving targets at night. Central to the tracking system is a high speed correlation algorithm to determine target motion between sensor image frames. Several issues complicate the correlation calculations. These include coherent speckle noise and atmosphere induced scintillation of the illuminator beam. The Fitts correlation algorithm is commonly used because of its simplicity and speed. However it is only optimal when the shift between sensor frames is less than a pixel. In addition it can be sensitive to certain types of noise. Projection based phase only (PBPO) is another type of correlation algorithm that is also high speed and in many cases less sensitive to noise. In this paper we compare the Fitts algorithm with PBPO in terms of number of computations and noise immunity when used in a LADAR tracker.

The Air Force Research Laboratory (AFRL) is developing and extending a model of the boundary layer that takes, as input, common atmospheric measurements and ground condition parameters, and predicts key parameters of optical turbulence such as strength and inner scale. In order to anchor the model, a field campaign is also being conducted. The campaign will include co-located meteorological instruments and an open loop Hartmann wavefront sensor. Here, a portion of the boundary layer model is discussed: that relevant for the daytime surface layer. A sensitivity analysis of input parameters is presented.

Recently a new technique for estimating the complex field in the pupil of a telescope from image-plane intensity measurements has been introduced by Codona.^{1, 2} The simplest form of the method uses two images of a point source, one with a small modification introduced in the pupil. The algorithm to recover the pupil field uses a functional derivative of the optical transfer function (OTF), and is simple and non-iterative. The derivative is approximated empirically by the difference between the Fourier transforms of the two PSFs: the differential OTF or dOTF. In keeping with the Hermitian symmetry of the OTF, the dOTF includes two conjugate copies of the pupil field overlapping at the point of modification. By placing the modification near the edge of the pupil, the overlap region can be kept small. It can be eliminated altogether by using a second modification and a third image. The technique can be used in broadband light, at the cost of blurring in the recovered phase that is proportional to the fractional bandwidth. Although the dOTF is unlikely to find application in high frame rate astronomical adaptive optics, it has many potential uses such as optical shop testing, non-common-path wavefront error estimation, segmented telescope phasing and general imaging system diagnostics. In this paper, we review the dOTF concept, theory, and initial experiments to demonstrate the technique.

Intensity Interferometry is a form of imaging developed in the 1950’s by Hanbury Brown and Twiss, which gave very early results for estimates of the diameters of stellar discs. It relies on the statistical properties of light to form an image by correlating the electronic signals measured independently and simultaneously at two or more separate collection telescopes. Its benefits are that it can provide very high resolution, can be very low in cost, does not require precision path matching, and is insensitive to atmospheric effects. Its disadvantages are that it has relatively poor SNR properties for larger telescope separations. An experiment is performed with three telescopes in Kihei, HI to investigate the potential for large-separation, high-resolution, multi-telescope operation. Simulations were performed to address key issues related to the experiment. Correlations were measured during lab checkouts, and also for early field testing. A compression scheme was developed to archive the raw data. The compression process had the added advantage of eliminating spurious electronic interference signals.

A dispersive transform spectral imager named FAROS (FAst Reconfigurable Optical Sensor) has been developed for high frame rate, moderate-to-high resolution hyperspectral imaging. A programmable digital micromirror array (DMA) modulator makes it possible to adjust spectral, temporal and spatial resolution in real time to achieve optimum tradeoff for dynamic monitoring requirements. The system’s F/2.8 collection optics produces diffraction-limited images in the mid-wave infrared (MWIR) spectral region. The optical system is based on a proprietary dual-pass Offner configuration with a single spherical mirror and a confocal spherical diffraction grating. FAROS fulfills two functions simultaneously: one output produces two-dimensional polychromatic imagery at the full focal plane array (FPA) frame rate for fast object acquisition and tracking, while the other output operates in parallel and produces variable-resolution spectral images via Hadamard transform encoding to assist in object discrimination and classification. The current version of the FAROS spectral imager is a multispectral technology demonstrator that operates in the MWIR with a 320 x 256 pixel InSb FPA running at 478 frames per second resulting in time resolution of several tens of milliseconds per hypercube. The instrument has been tested by monitoring small-scale rocket engine firings in outdoor environments. The instrument has no macro-scale moving parts, and conforms to a robust, small-volume and lightweight package, suitable for integration with small surveillance vehicles. The technology is also applicable to multispectral/hyperspectral imaging applications in diverse areas such as atmospheric contamination monitoring, agriculture, process control, and biomedical imaging, and can be adapted for use in any spectral domain from the ultraviolet (UV) to the LWIR region.

A new image restoration algorithm is proposed to remove the effect of atmospheric turbulence on motion-compensated frame averaged data collected by a three dimensional FLASH Laser Radar (LADAR) imaging system. The algorithm simultaneously arrives at an enhanced image as well as Fried's seeing parameter through an Expectation Maximization (EM) technique. Unlike blind deconvolution algorithms that operate only on two dimensional images, this technique accounts for both the spatial and temporal mixing that is caused by the atmosphere through which the system is imaging. Additionally, due to the over-determined nature of this problem, the point-spread function parameterized by Fried's seeing parameter can be deduced without the requirement for additional assumptions or constraints. The utility of the approach lies in its application to laser illuminated imaging where processing time is important.

The High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Laboratory employs a broadband wavefront correction algorithm called Electric Field Conjugation (EFC) to obtain the required 10-¹⁰ contrast. This algorithm works with one deformable mirror (DM) to estimate the electric-field to be controlled, and with one or multiple DM’s to create a “darkhole” in a predefined region of the image plane where terrestrial planets would be found. We have investigated the effects of absorbing dust particles on a flat optic, absorbing spots on the occulting mask, dead actuators on the DM, and the effects of control bandwidth on the efficiency of the EFC algorithm in a Lyot coronagraph configuration. The structural design of the optical system as well as the parameters of various optical elements used in the analysis is drawn from those of the HCIT system that have been implemented with one DM. The simulation takes into account the surface errors of various optical elements. Results of some of these studies have been verified by actual measurements.

Conventional multiphoton microscopy employs beam scanning; however, in this study a microscope based on spatiotemporal focusing offering widefield multiphoton excitation has been developed to provide fast optical sectioning images. The microscope integrates a 10 kHz repetition rate ultrafast amplifier featuring strong instantaneous peak power (maximum 400 μJ/pulse at 90 fs pulse width) with a TE-cooled, ultra-sensitive photon detecting, electron multiplying charge-coupled device camera. This configuration can produce multiphoton excited images with an excitation area larger than 200 × 100 μm2 at a frame rate greater than 100 Hz. Brownian motions of fluorescent microbeads as small as 0.5 μm have been instantaneously observed with a lateral spatial resolution of less than 0.5 μm and an axial resolution of approximately 3.5 μm. Moreover, we combine the widefield multiphoton microscopy with structure illuminated technique named HiLo to reject the background scattering noise to get better quality for bioimaging.

Unlike conventional multiphoton microscopy according to pixel by pixel point scanning, a widefield multiphoton microscope based on spatiotemporal focusing has been developed to provide fast optical sectioning images at a frame rate over 100 Hz. In order to overcome the aberrations of the widefield multiphoton microscope and the wavefront distortion from turbid biospecimens, an image-based adaptive optics system (AOS) was integrated. The feedback control signal of the AOS was acquired according to locally maximize image intensity, which were provided by the widefield multiphoton excited microscope, by using a hill climbing algorithm. Then, the control signal was utilized to drive a deformable mirror in such a way as to eliminate the aberration and distortion. A R6G-doped PMMA thin film is also increased by 3.7-fold. Furthermore, the TPEF image quality of 1 μm fluorescent beads sealed in agarose gel at different depths is improved.

The Standoff Intelligence Detection (SID) program is an Air Force Research Laboratory (AFRL) quick reaction program, tasked with providing the warfighter ready-now technologies related to directed energy, optics, and photonics. The first variant of these aircraft was started in 2008 utilizing two Cessna 182Q aircraft retrofitted with a wing mounted imaging systems and mission equipment. The 3rd generation of these imaging aircraft is equipped on a Cessna T-206H, Turbo Stationair. The aircraft is a 6-seat, single-engine aircraft, retrofitted with an MX-15HDi sensor system and supporting equipment.

The SID Program has produced the aircraft to provide an ISR platform to support tests, exercises, search and rescue, and real-world needs.

Recent advances in InGaAs camera technology has stimulated interest in the short wave infra-red (SWIR) band in the spectral region 0.84 – 1.7 μm. Located between the visible and thermal infra-red, the SWIR band shows interesting properties of both. Images tends to have the look of the visible and are less affected by scattering from aerosol haze, however the solar irradiance is dropping rapidly with wavelength in the SWIR. Spectral signatures, particularly of paints and dyes, may be different in the SWIR band compared to the visible. For these reasons we have chosen to investigate hyper-spectral measurements in this band using the NovaSol μHSI SWIR hyper-spectral imager system.

During the signal acquisition for synthetic aperture imaging ladar, any phase error will deteriorate the phase-matched filtering results. The phase differential algorithm (PDA) is presented to correct the phase error. The quadratic spatial phase history can be reconstructed from the phase information submerged by the phase error from platform line-of-sight translation–vibration and nonlinear chirp. The theoretical modeling results and experimental results are presented.

Synthetic aperture laser ladar is one of the most possible long-distance super-resolution active imaging methods. Many institutes have obtained two-dimensional synthetic aperture laser ladar’s reconstructed images. However, in these images, the laser speckle effect severely reduces the image quality. In the paper, we use mutli-receiver and multinoncoherent image superposition methods to reduce the impact of the laser speckle. According to the scalar diffraction theory, we deduced reconstructed image with the multi-receiver and the multi-noncoherent image superposition methods.

In synthetic aperture imaging ladar (SAIL), spatially and temporally varied speckles are resulted from the linear wavelength chirped laser signal. The random phase and amplitude of space-time speckle is imported to heterodyne beat signal by antenna aperture integration. The numerical evolution for such an effect is presented. Our research indicates the random phase and amplitude is closely related to the ratio of antenna aperture and speckle scale. According to computer simulation results, the scale design of optical antenna aperture to reduce the image degradation is proposed.

The cross-orbit scanning is very important for Fresnel telescope synthetic aperture imaging ladar system. This paper presents a design of large-angle high speed scanner based on electro-optic crystal for the cross-orbit scanning in Fresnel telescope synthetic aperture imaging ladar system. The designed scanner is based on the space-charge-controlled EO effect in KTN. In the experiment the crystal temperature should be kept a little higher above Tc to obtain a large EO effect and the polarization of the laser beam should be parallel to the direction of the driving electric field. Compared with other conventional EO crystal scanner, the new scanner can greatly improve the scanner angle by several times when maintains high speed and accuracy, which will have a great potential for cross-orbit scanning applications in Fresnel telescope synthetic aperture imaging ladar system.