Engineering Papers⌕ Search

Engineering topics

Yu, Jirong

Publications and source records attributed to Yu, Jirong.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Requirements and Technology Advances for Global Wind Measurement with a Coherent Lidar: A Shrinking Gap

Early concepts to globally measure vertical profiles of vector horizontal wind from space planned on an orbit height of 525 km, a single pulsed coherent Doppler lidar system to cover the full troposphere, and a continuously rotating telescope/scanner that mandated a vertical line of sight wind profile from each laser shot. Under these conditions system studies found that laser pulse energies of approximately 20 J at 10 Hz pulse repetition rate with a rotating telescope diameter of approximately 1.5 m was required. Further requirements to use solid state laser technology and an eyesafe wavelength led to the relatively new 2-micron solid state laser. With demonstrated pulse energies near 20 mJ at 5 Hz, and no demonstration of a rotating telescope maintaining diffraction limited performance in space, the technology gap between requirements and demonstration was formidable. Fortunately the involved scientists and engineers set out to reduce the gap, and through a combination of clever ideas and technology advances over the last 15 years, they have succeeded. This paper will detail the gap reducing factors and will present the current status.

Kavaya, Michael J.↗
NASA NTRS2007

Coherent Lidar Activities at NASA Langley Research Center

NASA Langley Research Center has been developing and using coherent lidar systems for many years. The current projects at LaRC are the Global Wind Observing Sounder (GWOS) mission preparation, the Laser Risk Reduction Program (LRRP), the Instrument Incubator Program (IIP) compact, rugged Doppler wind lidar project, the Autonomous precision Landing and Hazard detection and Avoidance Technology (ALHAT) project for lunar landing, and the Skywalker project to find and use thermals to extend UAV flight time. These five projects encompass coherent lidar technology development; characterization, validation, and calibration facilities; compact, rugged packaging; computer simulation; trade studies; data acquisition, processing, and display development; system demonstration; and space mission design. This paper will further discuss these activities at LaRC.

Kavaya, Michael J.↗
NASA NTRS2007

High Energy 2-micron Laser Developments

This viewgraph presentation shows the development of 2-micron solid state lasers. The topics covered include: 1) Overview 2-micron solid state lasers; 2) Modeling and population inversion measurement; 3) Side pump oscillator; and 4) One Joule 2-m Laser.

Yu, Jirong↗
NASA NTRS2007

High Energy 2-Micron Laser Developments

A master oscillator power amplifier, high energy Q-switched 2-micron laser system has been recently demonstrated. The laser and amplifiers are all designed in side-pumped rod configuration, pumped by back-cooled conductive packaged GaAlAs diode laser arrays. This 2-micron laser system provides nearly transform limited beam quality.

Yu, Jirong↗
NASA NTRS2007

Compact and Rugged Transceiver for Coherent Doppler Wind Lidar Applications in Space

High-accuracy, vertical profiles of the horizontal vector wind in earth s atmosphere, with the global coverage of an orbiting sensor, are a highly desired measurement of NASA, NOAA, and many other agencies and countries. It is the consensus of NASA and NOAA that the most cost effective, lowest risk measurement method with the earliest achievable mission date is the hybrid Doppler lidar method which utilizes both coherent- and direct-detection Doppler lidars to obtain the desired profiles. NASA Langley Research Center (LaRC) has advanced the 2-micron pulsed solid-state laser greatly over the past 15 years and has recently demonstrated 1.2 J of pulse energy whereas the requirement for a 400-km hybrid Doppler lidar mission is only 0.25 J. The IIP project reported here is an effort to increase the ruggedness and to compactly package the LaRC state-of-the-art laser technology.

Kavaya, Michael J.↗
NASA NTRS2007

2.5 MHz Line-Width High-energy, 2 Micrometer Coherent Wind Lidar Transmitter

2 micron solid-state lasers are the primary choice for coherent Doppler wind detection. As wind lidars, they are used for wake vortex and clear air turbulence detection providing air transport safety. In addition, 2 micron lasers are one of the candidates for CO2 detection lidars. The rich CO2 absorption line around 2 micron, combined with the long upper state life of time, has made Ho based 2 micron lasers a viable candidate for CO2 sensing DIAL instrument. The design and fabrication of a compact coherent laser radar transmitter for Troposphere wind sensing is under way. This system is hardened for ground as well as airborne applications. As a transmitter for a coherent wind lidar, this laser has stringent spectral line width and beam quality requirements. Although the absolute wavelength does not have to be fixed for wind detection, to maximize return signal, the output wavelength should avoid atmospheric CO2 and H2O absorption lines. The base line laser material is Ho:Tm:LuLF which is an isomorph of Ho:Tm:YLF. LuLF produces 20% more output power than Ho:Tm:YLF. In these materials the Tm absorption cross-section, the Ho emission cross-section, the Tm to Ho energy transfer parameters and the Ho (sup 5) I (sub 7) radiative life time are all identical. However, the improved performance of the LuLF is attributed to the lower thermal population in the (sup 5) I (sub 8) manifold. It also provides higher normal mode to Q-switch conversion than YLF at high pump energy indicating a lower up-conversion. The laser architecture is composed of a seed laser, a ring oscillator, and a double pass amplifier. The seed laser is a single longitudinal mode with a line width of 13 KHz. The 100mJ class oscillator is stretched to 3 meters to accommodate the line-width requirement without compromising the range resolution of the instrument. The amplifier is double passed to produce greater than 300mJ energy.

Petros, Mulugeta↗
NASA NTRS2007

Injection Seeded/Phase-Conjugated 2-micron Laser System

For the first time, beam quality improvement of 2 micron laser using a fiber based phase conjugation mirror has been demonstrated. Single frequency operation is necessary to lower threshold. The reflectivity of PCM is approx. 50%.

Bai, Yingxin↗
NASA NTRS2006

IIP Update: A Packaged Coherent Doppler Wind Lidar Transceiver. Doppler Aerosol WiNd Lidar (DAWN)

The state-of-the-art 2-micron coherent Doppler wind lidar breadboard at NASA/LaRC will be engineered and compactly packaged consistent with future aircraft flights. The packaged transceiver will be integrated into a coherent Doppler wind lidar system test bed at LaRC. Atmospheric wind measurements will be made to validate the packaged technology. This will greatly advance the coherent part of the hybrid Doppler wind lidar solution to the need for global tropospheric wind measurements.

Kavaya, Michael J.↗
NASA NTRS2006

Compact, Engineered, 2-Micron Coherent Doppler Wind Lidar Prototype for Field and Airborne Validation: Doppler Aerosol WiNd Lidar (DAWN). Interim Review #1 (6 months)

A new project, selected in 2005 by NASA's Science Mission Directorate (SMD), under the Instrument Incubator Program (IIP), will be described. The 3-year effort is intended to design, fabricate, and demonstrate a packaged, rugged, compact, space-qualifiable coherent Doppler wind lidar (DWL) transceiver capable of future validation in an aircraft and/or Unmanned Aerial Vehicle (UAV). The state-of-the-art 2-micron coherent DWL breadboard at NASA/LaRC will be engineered and compactly packaged consistent with future aircraft flights. The packaged transceiver will be integrated into a coherent DWL system test bed at LaRC. Atmospheric wind measurements will be made to validate the packaged technology. This will greatly advance the coherent part of the hybrid DWL solution to the need for global tropospheric wind measurements.

Kavaya, Michael J.↗
NASA NTRS2006

An Injection-seeded Narrow Linewidth Singly Resonant ZGP OPO

Injection seeding of a singly resonant ZnGeP2 (ZGP) mid-infrared optical parametric oscillator (OPO) using a continuous wave 3.39 micrometers laser and a tunable near-infrared laser has been demonstrated. This ZGP OPO utilizes a bow-tie shape cavity with a partially reflective mirror for injection seeding at the signal wavelength. It produces high energy pulses in the mid-IR range from 4-10 micrometers. The injection seeded OPO provides a narrow idler wavelength linewidth of approximately 1 nm, limited by the measurement resolution of the monochromator.

Yu, Jirong↗
NASA NTRS2006

A Narrow Linewidth Singly Resonant ZGP OPO for Multiple Lidar Applications

A singly resonant, injection seeded Zinc Germanium Phosphide (ZGP) optical parametric oscillator (OPO), capable to tune over 4.3-10.1 microns, is demonstrated. This ZGP OPO uses a bow-tie cavity with a partially reflective mirror for injection seeding at the signal wavelength. The injection seed source can be either a continuous wave 3.39 m laser or a tunable near-infrared OPO laser, which provides wide wavelength tuning capability. The injection seeded ZGP OPO narrows the idler wavelength linewidth to less than 1nm, limited by the measurement resolution of the monochromator. This device has potential to be used as a transmitter for multiple purpose lidar applications.

Yu, Jirong↗
NASA NTRS2006

Combined 2-micron Dial and Doppler Lidar: Application to the Atmosphere of Earth or Mars

A concept is explored for combining the Doppler and DIAL techniques into a single, multifunctional instrument. Wind, CO2 concentration, and aerosol density can all be measured. Technology to build this instrument is described, including the demonstration of a prototype lidar. Applications are described for use in the Earth science. The atmosphere of Mars can also be studied, and results from a recently-developed simulation model of performance in the Martian atmosphere are presented.

Singh, Upendra N.↗
NASA NTRS2006

Advanced 2-micron Solid-state Laser for Wind and CO2 Lidar Applications

Significant advancements in the 2-micron laser development have been made recently. Solid-state 2-micron laser is a key subsystem for a coherent Doppler lidar that measures the horizontal and vertical wind velocities with high precision and resolution. The same laser, after a few modifications, can also be used in a Differential Absorption Lidar (DIAL) system for measuring atmospheric CO2 concentration profiles. The world record 2-micron laser energy is demonstrated with an oscillator and two amplifiers system. It generates more than one joule per pulse energy with excellent beam quality. Based on the successful demonstration of a fully conductive cooled oscillator by using heat pipe technology, an improved fully conductively cooled 2-micron amplifier was designed, manufactured and integrated. It virtually eliminates the running coolant to increase the overall system efficiency and reliability. In addition to technology development and demonstration, a compact and engineering hardened 2-micron laser is under development. It is capable of producing 250 mJ at 10 Hz by an oscillator and one amplifier. This compact laser is expected to be integrated to a lidar system and take field measurements. The recent achievements push forward the readiness of such a laser system for space lidar applications. This paper will review the developments of the state-of-the-art solid-state 2-micron laser.

Yu, Jirong↗
NASA NTRS2006

High-Energy 2-Micrometers Doppler Lidar for Wind Measurements

High-energy 2-micrometer wavelength lasers have been incorporated in a prototype coherent Doppler lidar to test component technologies and explore applications for remote sensing of the atmosphere. Design of the lidar is presented including aspects in the laser transmitter, receiver, photodetector, and signal processing. Calibration tests and sample atmospheric data are presented on wind and aerosol profiling.

Koch, Grady J.↗