Terahertz local oscillator for the Microwave Limb Sounder on the Aura satellite

Abstract

The Microwave Limb Sounder on the Aura satellite has a radiometer at 2.5 THz to perform global mapping of OH in the atmosphere. The OH radiometer utilizes two Schottky-diode mixers pumped by an optically pumped THz gas laser local oscillator. The laser was first turned on in space on July 22, 2004, and has performed without issue for more than 30 months. The specifications, design, and modeling of this 2.5 THz laser local oscillator are presented here, along with some of the important design validation and test results.

THz QCLs for heterodyne receivers and wavelength modulation spectroscopy

“…The resulting detector signal has a standard deviation of 0. 6 8 Figure 5: Part (a) shows pyroelectric detector output after passing through frequency discriminator (i.e. frequency noise is now converted to amplitude noise) versus time for free running QCL (t = 0 to 220 s), frequency locked (t = 220 to 490 s) and with the QCL beam blocked (t > 490 s).…”

“…These requirements are further strained for arrays of detectors which scale scaling super linearly with the number. Above 2 THz, platforms such as EOS/AURA have used discrete lines provided by gas laser based local oscillators [6]. While the power levels of these devices can be >10 mW at certain frequency transitions, these sources are large, consume large amounts of power, cannot be continuously frequency tuned and have long-term stability issues that require complicated stabilization.…”

“…While the power levels of these devices can be >10 mW at certain frequency transitions, these sources are large, consume large amounts of power, cannot be continuously frequency tuned and have long-term stability issues that require complicated stabilization. As an alternative, a source with the following features is highly desirable [3,[6][7]: continuous-wave (CW) power output of >1 mW with single-mode operation, frequency-locked to within the detector IF bandwidth of the target gas (approximately <6 GHz), longterm frequency stability of ~100 kHz, frequency agility, allowing for the detection of multiple gas species, and a low size, weight and power consumption (SWaP).…”

Study of stable laser cavity with hole-coupling output mirror

“…Optically pumped THz lasers have been widely applied in the fields of THz imaging, security, medical and so on [1][2][3][4][5] . Compared to other optical and electronical methods of generating THz wave, the method of optically pumped THz laser owns the advantages of high efficiency and output power.…”

3.4 THz heterodyne receiver using a hot electron bolometer and a distributed feedback quantum cascade laser

“…Several space-borne or balloon-borne instruments have been constructed to detect OH lines. For example, NASA's Earth Observing System Microwave Limb Sounder ͑EOS-MLS͒, 2 based on a room-temperature Schottky diode as mixer and an optically pumped gas laser as LO, 3 is now operated to detect an OH line at 2.5 THz. Terahertz and submillimeter LImb Sounder ͑TELIS͒ is a three-channel balloon-borne heterodyne spectrometer for atmospheric research.…”