10:00 〜 10:15
[PCG21-05] Development of mid-IR heterodyne spectrometer with hollow fibers and the hollow fiber coupler for the observation of planetary atmospheres
キーワード：ヘテロダイン分光、中間赤外、分光器、金星大気、火星大気
Mid-infrared (IR) laser heterodyne spectroscopy can achieve an ultra-high wavelength resolution of λ/dλ>1,000,000 (frequency resolution <30 MHz) in the mid-IR wavelength of 10 μm (frequency of 30 THz). This enables to detect wind velocities in the planetary atmosphere directly with a resolution of several 10 m/s. The ultra-high resolution also has the capability to highly sensitive detections of trace gas and isotope ratios in the atmosphere. Notable successes on Venus, Mars, Titan, Jupiter, and Earth have been accomplished by ground-based telescopes with heterodyne spectrometers (e.g., Takami et al., 2020; Livengood et al., 2019; Kostiuk et al., 2001; Fast et al., 2002). However, these spectrometers require many optical elements to combine two optical paths, so their size and weight are large and their stability is not good. Because of this, the space-borne heterodyne spectrometer has never been achieved.
Fiber optics enables significant improvement to simplify, downsize, and reduce the weight of the instrument, leading to a breakthrough in space-borne applications. In the NIR region, the heterodyne system with fiber couplers has been proposed as a space-borne instrument (Rodin et al., 2015). On the other hand, in the mid-IR region, there has been no fiber coupler capable of achieving high transmission.
In this study, we focus on the development of a new Mid-IR laser heterodyne spectrometer using the hollow fiber coupler. It has a potential to be a space-borne system of the heterodyne spectrometer for future.
We have reported the feasibility studies of our new laser heterodyne spectrometer in the mid-IR region using fibers and a fiber coupler. (1) For the hollow fiber, transmission efficiencies of >85%/m were achieved for both CO2 gas laser and quantum cascade laser (QCL) as coherent light source. Meanwhile, transmission efficiency of 89.6%/m was achieved for sunlight as incoherent natural light source. (2) Heterodyne spectroscopy of lights from a black body and CO2 laser through fibers mixed by a beam splitter can achieve the similar sensitivity as that without fibers. (3) For the hollow fiber coupler, the heterodyne spectrometer using a CO2 laser as the Local Oscillator (LO) showed the system noise temperature (Tsys) was 1400K, which is close to the quantum noise limit. Tsys was calculated using the Y-factor method by applying the ratio of spectral power for black bodies with 673 K and 293 K. These results demonstrated for the first time the possibility of replacing conventional optical elements with hollow fiber optics for the IR heterodyne spectroscopy. For the next step, we are trying to observe terrestrial spectra of the CO2 around 10 μm. In the summer of 2024, we will also try to observe the Martian atmosphere and retrieve the amount of CO2 isotope ratio.
Fiber optics enables significant improvement to simplify, downsize, and reduce the weight of the instrument, leading to a breakthrough in space-borne applications. In the NIR region, the heterodyne system with fiber couplers has been proposed as a space-borne instrument (Rodin et al., 2015). On the other hand, in the mid-IR region, there has been no fiber coupler capable of achieving high transmission.
In this study, we focus on the development of a new Mid-IR laser heterodyne spectrometer using the hollow fiber coupler. It has a potential to be a space-borne system of the heterodyne spectrometer for future.
We have reported the feasibility studies of our new laser heterodyne spectrometer in the mid-IR region using fibers and a fiber coupler. (1) For the hollow fiber, transmission efficiencies of >85%/m were achieved for both CO2 gas laser and quantum cascade laser (QCL) as coherent light source. Meanwhile, transmission efficiency of 89.6%/m was achieved for sunlight as incoherent natural light source. (2) Heterodyne spectroscopy of lights from a black body and CO2 laser through fibers mixed by a beam splitter can achieve the similar sensitivity as that without fibers. (3) For the hollow fiber coupler, the heterodyne spectrometer using a CO2 laser as the Local Oscillator (LO) showed the system noise temperature (Tsys) was 1400K, which is close to the quantum noise limit. Tsys was calculated using the Y-factor method by applying the ratio of spectral power for black bodies with 673 K and 293 K. These results demonstrated for the first time the possibility of replacing conventional optical elements with hollow fiber optics for the IR heterodyne spectroscopy. For the next step, we are trying to observe terrestrial spectra of the CO2 around 10 μm. In the summer of 2024, we will also try to observe the Martian atmosphere and retrieve the amount of CO2 isotope ratio.