Mid-infrared laser heterodyne spectrometer by hollow optical fiber and its newly designed coupler.

We demonstrate a newly designed, to the best of our knowledge, hollow optical fiber coupler for a mid-infrared (IR) laser heterodyne spectrometer that mixes a targeted light source with local oscillator (LO) light. The hollow fiber achieves a high transmission efficiency ∼80-90%/m, not only for a coherent laser source but also for an incoherent blackbody source. The branching characteristics of the hollow optical fiber coupler are found to be strongly dependent on the curvature and length of the input port fiber, indicating that the branching ratio could be designed independently for each input port. Our laboratory measurements demonstrate that the branching ratio and transmittance of the coupler can be varied by coupling a flexible fiber to the input side owing to the excitation of higher-order modes. Using the hollow optical fiber coupler, a high-resolution emission spectrum of the quantum cascade laser at 10.3 µm for our C O 2 laser-based heterodyne spectrometer is successfully achieved. Using a C O 2 laser with a hollow fiber and a blackbody as a direct input signal in free space, we obtain the sensitivity performance of IR laser heterodyne spectrometer as 2000-3000 K of the system noise temperature. This suggests that the transmission of a coherent LO laser through a hollow optical fiber has almost the same sensitivity for the IR heterodyne detection as that without a fiber.

Alternate oscillations of Martian hydrogen and oxygen upper atmospheres during a major dust storm.

Dust storms on Mars play a role in transporting water from its lower to upper atmosphere, seasonally enhancing hydrogen escape. However, it remains unclear how water is diurnally transported during a dust storm and how its elements, hydrogen and oxygen, are subsequently influenced in the upper atmosphere. Here, we use multi-spacecraft and space telescope observations obtained during a major dust storm in Mars Year 33 to show that hydrogen abundance in the upper atmosphere gradually increases because of water supply above an altitude of 60 km, while oxygen abundance temporarily decreases via water ice absorption, catalytic loss, or downward transportation. Additionally, atmospheric waves modulate dust and water transportations, causing alternate oscillations of hydrogen and oxygen abundances in the upper atmosphere. If dust- and wave-driven couplings of the Martian lower and upper atmospheres are common in dust storms, with increasing escape of hydrogen, oxygen will less efficiently escape from the upper atmosphere, leading to a more oxidized atmosphere. These findings provide insights regarding Mars' water loss history and its redox state, which are crucial for understanding the Martian habitable environment.

Design for stray-light reduction to a Martian ionospheric imager.

We demonstrate a new design high-contrast optics suitable for use on a stray-light reduction. Two-dimensional distribution of diffracted light was numerically analyzed and confirmed by a laboratory measurement to determine its characteristics. Laboratory measurements confirm stray-light performance with ∼10-8 rejection viewing as close as 1.0° to a bright-light source. The present improvement replaces the conventional normal-edge vane by an edge with microscopic Gaussian-shaped structures. This permits simplified fabrication, provides even more weight reduction, and delivers improved performance for a given size.

Lunar radar sounder observations of subsurface layers under the nearside maria of the Moon.

Observations of the subsurface geology of the Moon help advance our understanding of lunar origin and evolution. Radar sounding from the Kaguya spacecraft has revealed subsurface layers at an apparent depth of several hundred meters in nearside maria. Comparison with the surface geology in the Serenitatis basin implies that the prominent echoes are probably from buried regolith layers accumulated during the depositional hiatus of mare basalts. The stratification indicates a tectonic quiescence between 3.55 and 2.84 billion years ago; mare ridges were formed subsequently. The basalts that accumulated during this quiet period have a total thickness of only a few hundred meters. These observations suggest that mascon loading did not produce the tectonics in Serenitatis after 3.55 billion years ago. Global cooling probably dominated the tectonics after 2.84 billion years ago.