We present progress on our holographic adaptive laser optics system (HALOS): a compact, closed-loop aberration
correction system that uses a multiplexed hologram to deconvolve the phase aberrations in an input beam. The wavefront
characterization is based on simple, parallel measurements of the intensity of fixed focal spots and does not require any
complex calculations. As such, the system does not require a computer and is thus much cheaper, less complex than
conventional approaches. We present details of a fully functional, closed-loop prototype incorporating a 32-element
MEMS mirror, operating at a bandwidth of over 10kHz. Additionally, since the all-optical sensing is made in parallel,
the speed is independent of actuator number - running at the same bandwidth for one actuator as for a million.
We present an adaptive optics system which uses a multiplexed hologram to deconvolve the phase aberrations in an input beam. The wavefront characterization is extremely fast as it is based on simple measurements of the intensity of focal spots and does not require any complex calculations. Furthermore, the system does not require a computer in the loop and is thus much cheaper, more compact and more robust as well. A fully functional, closed-loop prototype incorporating a 32-element MEMS mirror has been constructed. The unit has a footprint no larger than a laptop but runs at bandwidths over an order of magnitude faster than comparable, conventional systems occupying a significantly larger volume. Additionally, since the sensing is based on parallel, all-optical processing, the speed is independent of actuator number – running at the same bandwidth for one actuator as for a million.
We have created a new autonomous (computer-free) adaptive optics system using holographic modal wavefront sensing and closed-loop control of a MEMS deformable mirror (DM). A multiplexed hologram is recorded using the maximum and minimum actuator positions on the deformable mirror as the "modes". On reconstruction, an input beam is diffracted into pairs of focal spots and the ratio of the intensities of certain pairs determines the absolute wavefront phase at a particular actuator location. We present the results from an ultra-compact, 32-actuator prototype device operating at 100 kHz. It is largely insensitive to obscuration and has a speed independent of the number of actuators.
We have constructed an adaptive optics system incorporating a holographic wavefront sensor with the autonomous
closed-loop control of a MEMS deformable mirror (DM). HALOS incorporates a multiplexed holographic recording of
the response functions of each actuator in a deformable mirror. On reconstruction with an arbitrary input beam, pairs of
focal spots are produced. By measuring the relative intensities of these spots a full measurement of the absolute phase
can be constructed. Using fast photodiodes, direct feedback correction can be applied to the actuators.
We present results from a fast holographic adaptive laser optics system (HALOS) incorporating a MEMS-based
deformable mirror and an off-the-shelf, photon counting avalanche photodiode array. A simple digital circuit has been
constructed to provide autonomous control and the entire system is no larger than a shoebox. Our results demonstrate
that this device is largely insensitive to obscuration and in principle can run as fast with one actuator as with one million.
We further show how HALOS can be used in image correction, laser beam projection as well as phased-array beam
We have constructed a new type of modal wavefront sensor that uses a multiplexed hologram and position-sensing detectors to measure the amplitudes of a preselected set of eight Zernike modes in an input beam. The measurement is all optical, with the calculations made in encoding the holograms themselves. The result is a sensor with no computational overhead or postprocessing that has the potential to operate at megahertz speeds without the need for computer calculations. We have built and tested a prototype device, demonstrating its operation both as a stand-alone wavefront sensor and in a closed-loop adaptive optics control system.
We present results of a fast holographic wavefront sensor. The modal device consists of a multiplexed hologram
designed to diffract a single input beam into multiple output beams depending on the amplitude of particular Zernike
terms. The aberration and amplitude are determined by the spatial location and intensity of the reconstructed focused
spots. The sensing does not require any calculations, so the device is simple, compact and fast. In fact, using several
position sensing detectors (PSD), a full description of the wave aberration can be obtained at rates in excess of 100 kHz.
The holographic wavefront sensor can be reconfigured for any type of basis set, and is easily adaptable to laser mode
profiling. In this talk we will present results of the both the theory and operation of our holographic wavefront sensor.
We report a novel coherent beam combining technique. This is the first actively phase locked optical fiber array that eliminates the need for a separate reference beam. In addition, only a single photodetector is required. The far-field central spot of the array is imaged onto the photodetector to produce the phase control loop signals. Each leg of the fiber array is phase modulated with a separate RF frequency, thus tagging the optical phase shift for each leg by a separate RF frequency. The optical phase errors for the individual array legs are separated in the electronic domain. In contrast with the previous active phase locking techniques, in our system the reference beam is spatially overlapped with all the RF modulated fiber leg beams onto a single detector. The phase shift between the optical wave in the reference leg and in the RF modulated legs is measured separately in the electronic domain and the phase error signal is feedback to the LiNbO<sub>3</sub> phase modulator for that leg to minimize the phase error for that leg relative to the reference leg. The advantages of this technique are 1) the elimination of the reference beam and beam combination optics and 2) the electronic separation of the phase error signals without any degradation of the phase locking accuracy. We will present the first theoretical model for self-referenced LOCSET and describe experimental results for a 3 x 3 array.
A number of dithioacetate and dithiolate mono- and dianions have been synthesized and characterized through Z-scan measurements, with some showing significant third order nonlinear optical (NLO) behavior. Tetralkylphosphonium cations were utilized in tandem with the nonlinear anions so as to minimize electrostatic interactions within the salt, consequently resulting in the materials being room temperature ionic liquids (RTILs), which have numerous advantages over typical organic-based materials. Anions composed of metal-ligand systems were also tested for NLO behavior as components of novel ionic liquid materials. These RTILs introduce a new class of materials with potential applications in optical limiting and other all-optical devices.
We are studying ways to improve the performance of evanescent wave biosensors for use in detecting chemical and biological agents. We show a beam-propagation simulation that is used to determine the optimum fiber profile to achieve the desired propagation parameters. The model parameters can then be used to fabricate polymer fibers using an in-house fiber drawing apparatus. We also demonstrate a simple method of comparing the optical performance of different waveguides for use in such sensors.
The first second-harmonic generation field-induced molecular reorientation experiments in a dye-doped polymer in the 100 K to 500 K temperature range is reported. The (alpha) transition, related to the mobility of the polymer backbone, is easily observed. We also see evidence of the (beta) transition (attributed to side-chain mobility). We demonstrate the low- temperature end of our data suggests that the polymer acts as a rigid elastic constraint to the chromophore. We also observe what appears to be a spontaneously ordered phase of the doped polymer that ma be associated with the polymer/substrate interface. We report on the temperature-dependent phase transition of the transparent indium tin oxide electrode. Suggestions are made on separating the ITO contribution from the polymer response.