Kenji Numata

Frequency stabilization of distributed-feedback laser diodes at 1572 nm for lidar measurements of atmospheric carbon dioxide

We demonstrate a wavelength-locked laser source that rapidly steps through six wavelengths distributed across a 1572.335 nm carbon dioxide (CO(2)) absorption line to allow precise measurements of atmospheric CO(2) absorption. A distributed-feedback laser diode (DFB-LD) was frequency-locked to the CO(2) line center by using a frequency modulation technique, limiting its peak-to-peak frequency drift to 0.3 MHz at 0.8 s averaging time over 72 hours. Four online DFB-LDs were then offset locked to this laser using phase-locked loops, retaining virtually the same absolute frequency stability. These online and two offline DFB-LDs were subsequently amplitude switched and combined. This produced a precise wavelength-stepped laser pulse train, to be amplified for CO(2) measurements.

Performance of planar-waveguide external cavity laser for precision measurements

A 1542-nm planar-waveguide external cavity laser (PW-ECL) is shown to have a sufficiently low level of noise to be suitable for precision measurement applications. Its frequency noise and intensity noise was comparable or better than the non-planar ring oscillator (NPRO) and fiber laser between 0.1 mHz to 100 kHz. Controllability of the PW-ECL was demonstrated by stabilizing its frequency to acetylene ((13)C(2)H(2)) at 10(-13) level of Allan deviation. The PW-ECL also has the advantage of the compactness of a standard butterfly package, low cost, and a simple design consisting of a semiconductor gain media coupled to a planar-waveguide Bragg reflector.

Precision and fast wavelength tuning of a dynamically phase-locked widely-tunable laser

We report a precision and fast wavelength tuning technique demonstrated for a digital-supermode distributed Bragg reflector laser. The laser was dynamically offset-locked to a frequency-stabilized master laser using an optical phase-locked loop, enabling precision fast tuning to and from any frequencies within a ~40-GHz tuning range. The offset frequency noise was suppressed to the statically offset-locked level in less than ~40 μs upon each frequency switch, allowing the laser to retain the absolute frequency stability of the master laser. This technique satisfies stringent requirements for gas sensing lidars and enables other applications that require such well-controlled precision fast tuning.

Ground demonstration of trace gas lidar based on optical parametric amplifier

Abstract. We report on the development effort of a nanosecond-pulsed optical parametric amplifier (OPA) for remote trace gas measurements for Mars and Earth. The OPA output has ∼ 500     MHz linewidth and is widely tunable at both near-infrared and mid-infrared wavelengths, with an optical—optical conversion efficiency of up to ∼ 39 % . Using this laser source, we demonstrated open-path measurements of CH 4 (3291 and 1652 nm), CO 2 (1573 nm), H 2 O (1652 nm), and CO (4764 nm) on the ground. The simplicity, tunability, and power scalability of the OPA make it a strong candidate for general planetary lidar instruments, which will offer important information on the origins of the planet’s geology, atmosphere, and potential for biology.

Characteristics of the Single-Longitudinal-Mode Planar-Waveguide External Cavity Diode Laser at 1064 nm

We describe the characteristics of the planar-waveguide external cavity diode laser (PW-ECL). To the best of our knowledge, it is the first butterfly-packaged 1064 nm semiconductor laser that is stable enough to be locked to an external frequency reference. We evaluated its performance from the viewpoint of precision experiments. Using a hyperfine absorption line of iodine, we suppressed its frequency noise by a factor of up to 10(4) at 10 mHz. The PW-ECLs compactness and low cost make it a candidate to replace traditional Nd:YAG nonplanar ring oscillators and fiber lasers in applications that require a single longitudinal mode.

Frequency-tunable pre-stabilized lasers for LISA via sideband locking

Laser frequency noise mitigation is one of the most challenging aspects of the LISA interferometric measurement system. The unstabilized frequency fluctuations must be suppressed by roughly 12 orders of magnitude in order to achieve stability sufficient for gravitational wave detection. This enormous suppression will be achieved through a combination of stabilization and common-mode rejection techniques. The stabilization component will itself be achieved in two stages: pre-stabilization to a local optical reference followed by arm locking to some combination of the inter-spacecraft distances. In order for these two stabilization stages to work simultaneously, the lock-point of the pre-stabilization loop must be frequency tunable. The current baseline stabilization technique, Pound–Drever–Hall locking to an optical cavity, does not provide tunability between cavity resonances. Here we present a modification to the baseline technique that allows the laser to be locked to a cavity resonance with an adjustable frequency offset. This technique requires no modifications to the optical cavity itself, thus preserving the stability of the frequency reference. We present measurements of the system performance and demonstrate that the offset locking techniques are compatible with arm locking.

Spaceborne laser transmitters for remote sensing applications

NASA Goddard Space Flight Center (GSFC) has been engaging in Earth and planetary science remote sensing instruments development for many years. The latest instrument was launched in 2008 to the moon providing the most detailed topographic map of the lunar surface to-date. NASA GSFC is preparing for several future missions, which for the first time will perform active spectroscopic measurements from space. In this paper we will review the past, present and future of space-qualified lasers for remote sensing applications at GSFC.

Simple iodine reference at 1064 nm for absolute laser frequency determination in space applications

Using an iodine cell with fixed gas pressure, we built a simple frequency reference at 1064 nm with 10 MHz absolute accuracy and used it to demonstrate deterministic phase locking between two single-frequency lasers. The reference was designed to be as simple as possible, and it does not use a cooler or frequency modulator. This system should be useful, especially for space interferometric missions such as the Laser Interferometer Space Antenna.

Development of optical parametric amplifier for lidar measurements of trace gases on Earth and Mars

Trace gases in planetary atmospheres offer important clues as to the origins of the planets hydrology, geology, atmosphere, and potential for biology. We report on the development effort of a nanosecond-pulsed optical parametric amplifier (OPA) for remote trace gas measurements for Mars and Earth. The OPA output light is single frequency with high spectral purity and is widely tunable both at 1600 nm and 3300 nm with an optical-optical conversion efficiency of ~40%. We demonstrated open-path atmospheric measurements of CH4 (3291 nm and 1651 nm), CO2 (1573 nm), H2O (1652 nm) with this laser source.

Interferometric testbed for nanometer level stabilization of environmental motion over long time scales

We developed an interferometric testbed to stabilize environmental motions over time scales of several hours and a length scale of 1 m. Typically, thermal and seismic motions on the ground are larger than 1 microm over these scales, affecting the precision of more sensitive measurements. To suppress such motions, we built an active stabilization system composed of interferometric sensors, a hexapod actuator, and a frequency-stabilized laser. With this stabilized testbed, environmental motions were suppressed down to the nanometer level. This system will allow us to perform sensitive measurements, such as ground testing of the Laser Interferometer Space Antenna, in the presence of environmental noise.