Laser absorption spectroscopy combined with spectral analysis has been extensively investigated in detection and measurements of gas samples because of their broad applicability for measuring more than one hundred species, such as O₂, CO₂, H₂O, HCl, NH₃, NO_x, and hydrocarbons. Recently, real-time detection and measurements of gas samples based on laser absorption spectroscopy have attracted considerable interest from various fields owing to their performance of robustness, fast response speed, high sensitivity, and good precision. Here, we review the commonly used infrared laser absorption spectroscopy techniques for real-time measurements and the significant optical equipment utilized in measuring systems. Then, we discuss practical applications based on infrared laser absorption spectroscopy which require real-time determination of gas component concentrations, including atmospheric environment monitoring, breath analysis, combustion diagnostics, and industrial applications. Finally, perspectives of real-time determination of gas component concentrations based on infrared laser absorption spectroscopy are presented.

We report bound states of solitons from a harmonic mode-locked fiber laser based on a solution-processed graphene saturable absorber. Stable soliton pairs, 26.2 ps apart, are generated with 720 fs duration. By simply increasing the pump power, the laser can also generate harmonic mode-locking with harmonics up to the 26th order (409.6 MHz repetition rate). This is a simple, low-cost, all-fiber, versatile multifunction ultrafast laser that could be used for many applications.

Pulsed polarized vortex beams, a special form of structured light, are generated by tailoring the light beam spatiotemporally and witness the growing application demands in nonlinear optics such as ultrafast laser processing and surface plasma excitation. However, existing techniques for generating polarized vortex beams suffer from either low compactness due to the use of bulky components or limited controlment of pulse performance. Here, an all-fiber technique combining plasmonic metafibers with mode conversion method is harnessed to generate high-performance pulsed polarized vortex beams. Plasmonic metafibers are utilized as saturable absorbers to produce Q-switched pulses with micro-second duration, while the offset splicing method is employed to partially convert the fundamental transverse mode (LP $$_{01}$$01 ) to higher-order mode (LP $$_{11}$$11 ). Eventually, a polarized vortex beams laser is achieved at the telecom band with a repetition frequency of 116.0 kHz. The impact of geometrical parameters including period of metafibers and offset of splicing on the spatiotemporal properties of pulsed polarized vortex beams is systematically investigated. Our findings could pave the way for design, control and generation of all-fiber pulsed polarized vortex beams, and also offer insights into the development of other types of structured laser sources.