Demetrios Poulios

Space laser transmitter development for ICESat-2 mission

The first NASA Ice, Cloud and land Elevation Satellite (ICESat) was launched in January 2003 and placed into a nearpolar orbit whose primary mission was the global monitoring of the Earths ice sheet mass balance. ICESat has accumulated over 1.8 B shots in space and provided a valuable dataset in the study of ice sheet dynamics over the past few years. NASA is planning a follow-on mission ICESat-2 to be launched tentatively in 2015. In this paper we will discuss the development effort of the laser transmitters for the ICESat-2 mission.

Laser transmitter development for NASA's Global Ecosystem Dynamics Investigation (GEDI) lidar

The Global Ecosystems Dynamics Investigation (GEDI) Lidar, to be installed aboard the International Space Station in early 2018, will use 3 NASA laser transmitters to produce 14 parallel tracks of 25 m footprints on the Earths surface. A global set of systematic canopy measurements will be derived, the most important of which are vegetation canopy top heights and the vertical distribution of canopy structure. Every digitized laser pulse waveform will provide 3-D biomass information for the duration of the mission. A total of 5 GEDI-HOMER lasers are to be built (1 ETU + 3 Flight + 1 spare) in-house at NASA-GSFC, and is based on a well-studied architecture, developed over several years in the Lasers and Electro-Optics Branch.

Lifetest of the High Output Maximum Efficiency Resonator (HOMER) laser for the SAFFIRE instrument on NASA's DESDynI project

We update the status of a diode-pumped, Nd:YAG oscillator that is the prototype laser for NASAs DESDynl mission. After completing TRL-6 testing, this laser has fired over 5.5 billion shots in lifetesting.

Q-switched rate equations for diode side-pumped slab and zigzag slab lasers including Gaussian beam shapes

A set of rate equations accounting for the transverse spatial distributions of both the laser mode and inversion density is developed for side-pumped Q-switched oscillators. The equations can be reduced to a simple form by assuming a Gaussian laser mode, a one-dimensional Gaussian pump beam and a few additional basic assumptions, allowing for rapid numerical solution. The derived spatial rate equations are then used to model an experimentally well-characterized Nd/sup +3/:YAG zigzag slab laser to demonstrate their simplicity and accuracy in predicting oscillator performance.

Performance of multilayer optical coatings under long-term 532nm laser exposure

The effects of long-term exposure to high intensity 532 nm radiation on various dielectric-coated optics are studied. To investigate potential photodarkening effects on optical surfaces, an accelerated life test platform was constructed where optics were exposed to 532 nm radiation from a short-pulse, high repetition rate fiber amplifier at total doses up to 1 trillion shots. The first run of trillion-shot tests were conducted on e-beam deposited and ion beam sputtering (IBS) coated high reflecting mirrors with onsurface intensities ranging from 1.0-1.4 GW/cm2. It was found that the e-beam coated mirrors failed catastrophically at less than 150 billion shots, while the IBS coated mirror was able to complete the trillionshot test with no measurable loss of reflectivity. Profiling the IBS mirror surface with a high-resolution white light interferometer post-irradiation revealed a ~10 nm high photocontamination deposit at the irradiation site that closely matched the intensity profile of the laser spot. Trillion-shot surface exposure tests were also conducted at multiple surface sites of an LBO frequency doubling crystal at ~1.5 GW/cm2 at multiple surface sites. The transmitted power and on-surface beam size were monitored throughout the tests, and periodic measurements of the beam quality and waist location of the transmitted light were also made using an M2 meter. No changes in transmitted power or M2 were observed in any of the tests, but 3D surface profiling revealed laser-induced contamination deposits at each site tested.

Derivation of the Frantz-Nodvik Equation for Diode-Side-Pumped Zigzag Slab Laser Amplifiers With Gaussian Laser Mode and Pump Beam Shapes

The theory for Gaussian beam pulse propagation in a zigzag slab amplifier with a Gaussian pump distribution is detailed. Provisions are made for amplification of an input signal with an elliptical Gaussian spatial mode by modifying the time-dependent photon transport equations as described by Eggleston Frantz, and Injeyan. A comparison is made with experimental results of a diode-side-pumped zigzag slab amplifier element amplifying a near-Gaussian beam.

100 mJ Q-switched, high efficiency, high brightness Nd:YAG oscillator: Wavefront analysis

A diode-pumped, 100 mJ/pulse, Nd:YAG oscillator employing a dual pump head design aligned orthogonally in an unstable resonator configuration producing aperture-free TEM00 beams is presented.

A diode pumped, Nd:YAG, Q-switched unstable resonator developed for multi-billion shot, spaced based remote sensing applications

This highly efficient Nd:YAG laser was designed as a prototype NASA-funded transmitter for space-based LIDAR missions. This design completed a 4.8 billion shot lifetest at 242 Hz with 10-15 mJ per pulse and 10 ns pulsewidth.

A mission-enabling UV laser for mass spectrometry (UVMS) with continuously selectable output for in-situ planetary exploration

Ultra-compact, nanosecond-class spaceflight-compatible UV lasers are finding increasing application in laser desorption, excitation, and ionization analytical applications on planetary missions, such as the detection and characterization of potential molecular biosignatures on Mars or icy moon surfaces. A short pulsed, solid state, UV laser is under development with selectable pulse energy capabilities for optimized sample ion production at a planetary surface.

Qualification of the solid state laser systems for the GEDI altimeter mission

The Global Ecosystems Dynamics Investigation (GEDI) Lidar Mission will employ three lasers systems internally developed, built, and tested by the NASA Goddard Space Flight Center Lasers and Electro-Optics Branch. Once installed on the Japanese Experiment Module (JEM) on the International Space Station (ISS), the lasers, each coupled with a Beam Dithering Unit (BDU) will produce three sets of staggered footprints on the Earths surface to accurately measure global biomass. Each of the lasers is a heritage Nd:Yag solid state design required to put out Q-switched pulses at a rate of 242 Hz with a minimum 10 mJ per pulse at a 1064 nm wavelength. During the project, an engineering test unit (ETU) was also built and tested to pave the way for the laser systems to be used in space. We report on the technical and programmatic requirements that drove the design and development of the lasers. Also presented is an update of the performance of the engineering test unit qualification and life-testing along with the status of the space flight lasers.