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A 40-element array of antiguided laser diodes was constructed, which produced a peak power of 11.5 W in an in-phase radiation pattern. The laser has a threshold current of 0.5 A and a differential efficiency of 50 percent. It achieves the output power of 11.5 W at an input current of 18 A. The FWHM of the central lobe of the device at the output power of 11.5 W is 1.0 deg.
The NASA ARTEMIS Program will include LunaNet, a highly extensible, open architecture, lunar communications and navigation network. A constellation of CubeSats in Low Lunar Orbit (LLO), 100 km, could form an optical communications and navigation network as part of LunaNet, with terminals on the lunar surface, including mobile ones such as with astronauts and rovers. The proposed CubeSat nodes should provide data relay and navigational aid services. The proposed effort herein is to develop a fine pointing capability for laser beam pointing to augment body pointing by CubeSats. Body pointing was used by Aerospace Corporation for the CubeSats in LEO in NASA’s Optical Communications and Sensors Demonstration (OCSD) program [1]. Previously, this fine pointing capability was computer simulated for the OCSD program [2,3]. With fine pointing, the spot size on the Earth was reduced by a factor of eight with a reduction in laser output power by a factor of sixty-four, thereby mitigating the thermal load challenge on the CubeSats. The same reductions in spot size and laser output power can be achieved for CubeSats in LLO. A new method is described for optical data transmissions from satellites, which uses laser arrays for laser beam pointing. It combines a lens system and an array of vertical-cavity, surface-emitting lasers and photodetectors, an VCSEL/Photodetector Array, (both mature technologies), in a novel way. This system is applied to CubeSats in low lunar orbit, (LLO), which use body pointing. Also, It may be able to replace current architectures which use dynamical systems, (i.e., moving parts) to point the laser, and which may also use vibration isolation platforms. The computer simulations used the optics code, OpticStudio, from Zemax, LLC, which has the capabilities to model the laser source and diffraction effects from wave optics. These capabilities make it possible to model laser beam propagation over long space communication distances.
This viewgraph presentation reviews a study that aimed at a characterization of the Quasi-CW Laser Diode Arrays. NASA's requirements for high reliability, high performance satellite laser instruments have driven the investigation of many critical components; specifically, 808 nm laser diode array (LDA) pump devices. Performance and comprehensive characterization data of Quasi-CW, High-power, laser diode arrays is presented
The time evolution of the far-field radiation pattern of an in-phase locked Y-coupled diode laser array has been observed with a streak camera. A strong central lobe 2.3 deg wide with faint secondary sidelobes separated by 15 deg forms in a time less than 20 ps. This indicates that the elements of the array are instantaneously locked in-phase.
Reliability and lifetime of quasi-CW laser diode arrays are greatly influenced by their thermal characteristics. This paper examines the thermal properties of laser diode arrays operating in long pulse duration regime.
The prelaunch testing performed on the Geos-3 laser reflector array before launch was used to determine the lidar cross section of the array and the distance of the center of gravity of the satellite from the center of gravity of reflected laser pulses as a function of incidence angle. Experimental data are compared to computed results.
Time-resolved optical and thermal analyses of laser diode arrays reveals temperature induced chirp and the presence of anomalous hot spots.
The LRCTF (Laser Ranging Characterization and Test Facility) is a unique facility built at NASA GSFC to provide thermal-optical testing of the next generation GPS LRA (Global Positioning Satellite’s Laser Retroreflector Array) laser ranging target. The 400mm diameter target is an array consisting of 48 total internal reflection retroreflectors and has an optical cross section requirement of 100 MSM (million square meters). To verify that the array meets this requirement during on-orbit conditions, the LRCTF is equipped with a 400mm test beam, a data product output consisting of full aperture FFDPs (Far Field Diffraction Patterns) and a thermal chamber. The FFDPs are used to calculate the OCS. This paper will describe the facility design, alignment approach, and verification process.
High-power laser diode arrays (LDAs) are used for a variety of space-based remote sensor laser programs as an energy source for diode-pumped solid-state lasers. LDAs have been flown on NASA missions including MOLA, GLAS and MLA and have continued to be viewed as an important part of the laser-based instrument component suite. There are currently no military or NASA-grade, -specified, or - qualified LDAs available for "off-the-shelf" use by NASA programs. There has also been no prior attempt to define a standard screening and qualification test flow for LDAs for space applications. Initial reliability studies have also produced good results from an optical performance and stability standpoint. Usage experience has shown, howeve that the current designs being offered may be susceptible to catastrophic failures due to their physical construction (packaging) combined with the electro-optical operational modes and the environmental factors of space application. design combined with operational mode was at the root of the failures which have greatly reduced the functionality of the GLAS instrument. The continued need for LDAs for laser-based science instruments and past catastrophic failures of this part type demand examination of LDAs in a manner which enables NASA to select, buy, validate and apply them in a manner which poses as little risk to the success of the mission as possible.
The far-field beam pattern and the power-collection efficiency are calculated for a multistage laser-diode-array amplifier consisting of about 200,000 5-W laser diode arrays with random distributions of phase and orientation errors and random diode failures. From the numerical calculation it is found that the far-field beam pattern is little affected by random failures of up to 20 percent of the laser diodes with reference of 80 percent receiving efficiency in the center spot. The random differences in phases among laser diodes due to probable manufacturing errors is allowed to about 0.2 times the wavelength. The maximum allowable orientation error is about 20 percent of the diffraction angle of a single laser diode aperture (about 1 cm). The preliminary results indicate that the amplifier could be used for space beam-power transmission with an efficiency of about 80 percent for a moderate-size (3-m-diameter) receiver placed at a distance of less than 50,000 km.
An important need, especially for space-borne applications, is the early identification and rejection of laser diode arrays which may fail prematurely. The search for reliable failure predictors is ongoing and has led to the development of two techniques, infrared imagery and monitoring the Temporally-resolved and Spectrally-Resolved (TSR) optical output from which temperature of the device can be measured. This is in addition to power monitoring on long term burn stations. A direct measurement of the temperature of the active region is an important parameter as the lifetime of Laser Diode Arrays (LDA) decreases exponentially with increasing temperature. We measure the temperature from time-resolving the spectral emission in an analogous method to Voss et al. In this paper we briefly discuss the measurement setup and present temperature data derived from thermal images and TSR data for two differently designed high-power 808 nanometer LDA packages of similar specification operated in an electrical and thermal environment that mimic the expected operational conditions.
Systematic co-location in space through the precision orbit determination of GPS satellites via satellite laser ranging will contribute significantly towards improving the accuracy and stability of the international terrestrial reference frame. NASA recently formed the GPS Laser Retroreflector Array Project to develop and deliver retroreflectors for integration on the next generation of GPS satellites. These retroreflectors will be an important contributor to achieving a global accuracy of 1.0 mm and 0.1 mm/year stability in the international terrestrial reference frame. We report here the current status of the GPS Laser Retroreflector Array Project.
The electro-optic switching properties of injection-coupled coherent 2-D grating-surface-emitting laser arrays with multiple gain sections and quantum well active layers are discussed and demonstrated. Within such an array of injection-coupled grating-surface-emitting lasers, a single gain section can be operated as intra-cavity saturable loss element that can modulate the output of the entire array. Experimental results demonstrate efficient sub-nanosecond switching of high power grading-surface-emitting laser arrays by using only one gain section as an intra-cavity loss modulator.
Spectra taken for a pulsed variable spacing phase-locked laser diode array (VSA) were recorded and processed to determine the magnitude of wavelength fluctuations present in the diode's output field. Analysis revealed that a pulsed VSA emits primarily into a single longitudinal mode.
Oscillations synchronized and modulated individually for beam steering. Phased array of GaAs infrared lasers put out powerful electronically-steerable coherent beam. Fabricated as integrated circuit on GaAs chip, new device particularly suited to optical communications, optical data processing and optical detection and ranging systems.
The output power from two ten-element laser diodes arrays has been efficiently summed in an external cavity to obtain a coherent, continuous wave beam. In this technique, laser emission from each front surface antireflection coated diode array is stimulated by injection of emission from a second such array. This method was also applied to single-element diode lasers. The output beam characteristics such as spectral distribution, far-field and near-field beam patterns, and overall efficiency have been measured.
The development of individually addressable laser diode arrays for multitrack magneto-optic recorders for space stations is discussed. Three multi-element channeled substrate planar (CSP) arrays with output power greater than 30 mW with linear light vs current characteristics and stable single mode spectra were delivered to NASA. These devices have been used to demonstrate for the first time the simultaneous recording of eight data tracks on a 14-inch magneto-optic erasable disk. The yield of these devices is low, mainly due to non-uniformities inherent to the LPE growth that was used to fabricate them. The authors have recently developed the inverted CSP, based on the much more uniform MOCVD growth techniques, and have made low threshold quantum well arrays requiring about three times less current than the CSP to deliver 30 mW CW in a single spatial mode. The inverted CSP is very promising for use in space flight recorder applications.
Phase-coherent emission with negligible far-field supermodes produced by proposed surface-emitting laser-diode array stimulated by holographically directed emission from single master diode. To achieve same coherence and output power, single laser diode requires high power density, which substantially reduces working lifetime. Proposed integrated optical array useful in communications