Metastable helium lidar represents a promising technique for upper atmospheric detection; however, its implementation entails several critical scientific challenges that necessitate thorough experimental validation and refinement under controlled laboratory conditions. To address this need, we have developed a dedicated laboratory simulation instrument comprising three key components: (1) a metastable helium source chamber, (2) an integrated transmitter and receiver system, and (3) a precise experimental timing sequence. The metastable helium source, housed within the main vacuum chamber, is a pulsed supersonic plasma jet generated via gas discharge. The integrated transmitter and receiver emulate a lidar configuration, enabling the investigation of the backward fluorescence spectrum of metastable helium. The experimental timing sequence governs the operation of individual components and facilitates baseline noise subtraction through precise temporal alignment. A direct absorption spectroscopy detection scheme can also be implemented on the setup to perform calibration experiments. The system achieves a metastable helium atom density of ∼1010 cm-3. The density, velocity distribution, and flow speed of metastable helium atoms in the source can be controlled by changing the discharge nozzle configuration and discharge conditions. This simulation instrument enables the investigation of the saturation effect in the absorption spectrum of metastable helium atoms, providing valuable laboratory data for the design and data analysis of helium lidar systems. Ultimately, it also serves as a calibration tool for both ground-based and future spaceborne helium lidar devices.
Wang et al. (Sun,) studied this question.