S. Wu’s research while affiliated with China Institute of Atomic Energy and other places

We report on the design philosophy, technology readiness level advancement for space application, laser performance verification, and independent assessment of a single frequency, ultra-low noise master oscillator power amplifier laser transmitter for the LISA mission.

Trace gases and their isotopic ratios in planetary atmospheres offer important but subtle clues as to the origins of a planet's atmosphere, hydrology, geology, and potential for biology. Calculations show that an orbiting laser remote sensing instrument is capable of measuring trace gases on a global scale with unprecedented accuracy, and higher spatial resolution that can be obtained by passive instruments. Our proposed lidar uses Integrated Path Differential Absorption technique, Optical Parametric Amplifiers, and a receiver with high sensitivity detector at 1.65 μm to map methane concentrations, a strong greenhouse gas. For Mars we can use the same technique in the 3–4 μm spectral range to map various biogenic gas concentrations and search for the existence of life. Preliminary results demonstrating methane and water vapour detection using a laboratory prototype illustrate the viability of the technique.

We report on remote sensing measurements of methane using a widely tunable, seeded optical parametric generator (OPG). Laser remote sensing measurements of trace gases from orbit can provide unprecedented information about important earth science and planetary science. On Earth, our current observations of most trace gases are limited to in-situ (surface and tower sites) and sparse airborne measurements. Although CO2 is currently the primary greenhouse trace gas of concern, other trace gases such as methane may have a much larger impact on climate change. Although methane survives for a shorter time in the atmosphere than CO2 its impact on climate change can be more than 20 times than that of CO2. Methane levels have remained relatively constant over the last decade around 1.78 parts per million (ppm) but recent observations indicate that levels may be on the rise. A current hypothesis holds that vast reservoirs of methane are trapped in the permafrost regions of northern Canada, Europe, and Siberia and as global temperatures rise and the permafrost thaws, enormous amounts of methane will be released into the atmosphere affecting the vegetation and ecosystems. Another hypothesis points to increased production of methane by microbes as the permafrost warms up and temperatures rise. Although the exact mechanism may still be uncertain its implications are not: Increasing methane concentrations can trigger a positive feedback effect where increasing temperatures result in increasing methane levels creating a “runaway” greenhouse effect. The NRC Decadal Survey recognized the importance of global observations of greenhouse gases and explicitly called for simultaneous CH4, CO, and CO2 measurements but also underlined the technological limitations for methane observations. We will report on remote sensing measurements of methane using a high peak power, widely tunable optical parametric generator (OPG) operating at 1.65 um. The OPG is pumped by a passively q-switched single frequency laser (3ns, 5KHz, 50uJ) and seed by a diode laser. The spectral width of both signal and idler of seeded OPG is near Fourier transform limited, ~400 MHz. The output of seeded OPG is single frequency with high spectral purity and is widely tunable. Both 1650nm and 3300 nm can be generated with a conversion efficiency of more than 30%. Methane also has strong absorptions in the 3300 nm spectral region. This spectral region is ideal for planetary applications, where the detection of biogenic molecules, such as Methane, has important implications on the existence of life. We have demonstrated detection of methane at 3274 nm in a cell and also performed open path atmospheric measurements of CH4 at the same wavelength. Finally, we were able to demonstrate simultaneous detection of methane at 3270.4 nm and CO2 at 1578.2 nm. In this paper we will discuss the OPG performance and atmospheric open path measurement results.

Measurements of CO2 mixing ratios within the planetary boundary layer will be required to validate the performance of the future ASCENDS instrument. We have adapted the well-known DIAL technique to measure CO2 mixing ratios with the PBL using the 1570 nm band of CO2 and an Optical Parametric Amplifier (OPA). The short-term focus of this effort is the development and demonstration of the technique and the technology required to make these measurements. The long-term goal is the development of a inexpensive, compact instrument constructed out of commercial off the shelf components capable of making these measurements remotely from any suitable location. The approach employs a single, distributed feedback laser, as the signal source for an OPA. The OPA, pumped by a Nd:YAG laser, converts pump photons at 1064 nm into signal photons at the wavelength of interest - 1572.335 nm. A breadboard version of the instrument has been developed and measurements made. These measurements extend over multiple days and have permitted us to assess the performance of the instrument and compare its results to those of a collocated CO2 sensor. Representative samples of the data will be presented as will an assessment of the current technology.

InGaAs APDs with improved photon counting characteristics were designed and fabricated and their performance improvements were observed. Following the results, a 4times4 individually addressable APD array was designed, fabricated, and results are reported