Developed for the Army's White Sands Missile Range, this precision zoom lens consists of 16 refractive elements with three stationary lens groups and two moving lens groups. Using optical compensation, the focus and zoom are simultaneously maintained for focal lengths from 750 mm (f/4) to 3800 mm (f/14) at a resolution of 100 line pairs/mm (lp/mm) and an image field of 24 mm. The throughput of the lens is ~85%, and the lens is optimized over the visible waveband
(485 nm to 650 nm). The zoom lens images objects at distances from 0.7 km to 100 km and is thermally compensated over a temperature range of 20 °F to 120 °F. Optical assembly was accomplished in about a week.
We designed an electro-optical relay system to perform nonmechanical beam switching in the mid-infrared waveband and built a proof-of-concept prototype to verify the system performance. The prototype is a scalable building block that can be used to fabricate a two-dimensional system to scan a large field of regard at high resolution, low power, and high speed. We designed, fabricated, and tested the major components and then assembled the components into the electro- optical relay system, which demonstrated 8 kHz switching between two fields of view. In order to implement the system, we fabricated mid-wave infrared polarizing beamsplitter cubes that provided excellent polarization separation over a 600 nm waveband and a range of angles of incidence. Additionally, we demonstrated 90 degree polarization rotation in the mid-wave infrared waveband using ferroelectric liquid crystals.
We have devised a nonmechanical beam-scanning system to subdivide a large field of regard into smaller fields of view and then to image these individual fields of view with high resolution. Selection of the individual fields of view is performed by spatially multiplexing the fields of view through an optical relay system onto a single camera. Selection of a particular field of view is accomplished by a series of ferroelectric liquid-crystal half-wave plates. We designed our beam-scanning system to cover a 3 degree multiplied by 12 degree field of regard in the mid-infrared waveband, and we built a proof-of-concept prototype to verify system performance. The prototype is a scalable building block that can be used to fabricate a two-dimensional system to scan a large field of regard at high resolution, low power, and high speed. We also describe how such a beam-scanning system can be combined with galvanometer-driven mirrors to produce a hybrid system that incorporates the advantages of both types of systems and minimizes the drawbacks of either system for very large fields of regard.
The diffraction efficiencies of binary-optics lenses with low f/#'s deviate from predictions of scalar diffraction theory. To increase the diffraction efficiencies for low f/#'s, vector diffraction theory is necessary. In this paper, we describe the design and fabrication of a 30 x 50 array of f/1 binary-optics microlenses using direct-write electron-beam lithography and reactive-ion etching. The diameter of each lens is 160 μm, and the focal length is 165 μm. The center-to-center spacing between the lenses is 300 μm, and they are fabricated in fused silica. The measured diffraction efficiency for an elliptical Gaussian beam is 80% for lenses designed using vector diffraction theory and 63% for lenses designed using scalar diffraction theory.
We analyzed the optical and mechanical performance of several designs of agile beam steerers based on refractive microlens arrays for sensing and imaging applications in the visible and infrared wavebands. Ray-trace analyses showed that the best design is capable of steering narrowband illumination +/- 25 degree(s) in two dimensions with nearly diffraction-limited performance. The maximum steering angle depends on the materials. We found that imaging the field of regard takes significantly more time than scanning it unless cameras with very high frame-rates are used. We performed many parametric studies that can be used to optimize the design for any application. We compared optimal designs for microlens-array and conventional galvanometric agile beam steerers. The microlens-array agile beam steerer provides significant improvements in scanning speed, random access pointing, energy consumption, mass reduction, and volume reduction.
We demonstrate the phase locking of a 12 X 12 two-dimensional surface emitting laser array to generate 1.4 W of output power in diffraction limited far-field. A phase contrast imaging system is used to measure array element phases and apply corrections to an intracavity liquid crystal array.
This paper describes phasing of semiconductor laser arrays placed in an external Talbot cavity for high coherent output power. The external Talbot cavity couples the light between many adjacent lasers such that all lasers operate at the same frequency and phase, resulting in a high power diffraction limited output beam. We first verified the concepts of the Talbot cavity exploiting a simple 1-D Talbot cavity with 20 elements and demonstrated over 600 mW cw total output power in a diffraction limited output beam. In order to fabricate a highly scalable 2-D phased array of lasers, a new type of monolithic 2-D surface emitter was developed for the 2-D Talbot cavity. We have demonstrated 50 W cw output power from a nonphased 2-D monolithic surface emitting laser array with 1500 laser elements. Finally, using a similar 2-D 12 by 12 element surface emitting laser array, we demonstrated 2-D coherence from a compact 2-D Talbot cavity which includes a GaP mass transport lens array, a liquid crystal array and a phase sensing and control system.
A method was developed for sensing the phases of a two-dimensional array of coherent sources. The method is based upon phase contrast imaging and was developed to correct the phases of individual GaAlAs emitters in a two-dimensional external cavity laser array. This paper describes the method and presents results for an 18-element linear Talbot laser cavity and for an experimentally simulated 12 x 12 array. Phase correction was achieved using a nematic liquid crystal array.
This paper describes semiconductor laser arrays placed in an external Talbot cavity. The external Talbot cavity couples the light between many adjacent lasers such that all lasers operate at the same frequency and phase, resulting in a high power diffraction limited output beam. We designed a compact cavity which is comprised of a 30 by 50 element monolithic 2-D laser array, a GaP mass transport lens array, a liquid crystal array, a phase sensing and control system and a waveguide. Initial results obtained from a 20 element linear Ta1bOt cavity with a calculated mode discrimination similar to the 2-D
cavity demonstrate in excess of 30 mW cw per laser element in a diffraction limited far field. In addition we have also demonstrated 50 Watt CW incoherent output power from a monolithic 2D laser array
A seven-element gain-guided AlGaAs diode laser array is used to establish an external cavity which relies on weak diffractive coupling for its operation. Collimation of the lasers is achieved using a binary-optics microlens array. A nematic liquid crystal phase modulator is placed in the image plane of the lenslet array to provide individual phase control of each laser stripe. It is shown that the liquid crystal phase modulator is capable of establishing partial coherence by independent adjustment of the laser optical path lengths.
We demonstrate two-dimensional optical wide angle beam steering by incorporating two steering techniques in
tandem. The first technique is translation of two microlens arrays configured as a telescope array. The microlens
translation produces wide angle steering to discrete angles. The second technique is optical phased array steering
using a nematic liquid crystal array, which provides access to a continuous range of angles. By translating both
microlens arrays of the 10 x 10 telescope array, we demonstrate steering to maintaining a peak irradiance
within 3.6 dB of the on-axis peak irradiance.