In the field of absorption spectroscopy, the multipass cell (MPC) is one of the key elements. It has the advantages of simple structure, easy adjustment, and high spectral coverage, which is an effective way to improve the detection sensitivity of gas sensing systems such as tunable diode laser absorption spectroscopy. This invited paper summarizes the design theory and the research results of some mainstream types of MPCs based on two mirrors and more than two mirrors in recent years, and briefly introduces the application of some processed products. The design theory of modified ABCD matrix and vector reflection principle are explained in detail. Finally, trends in its development are predicted.

The aggregation and photoinduced excited state dynamics of organic π-conjugated molecules play a vital role in solar energy conversion and applications. This work investigates how solvent polarity affects the aggregation behavior and the photophysical process of perylene diimide dimer (PDI-II). The results show that the conjugations between PDI intramolecular chromophores are more likely to generate excimer, and the conjugations between PDI intermolecular chromophores are more likely to experience symmetry-breaking charge separation. Our study can provide a reference for the design of high-efficiency solar energy conversion materials.