## 1 Introduction  
Microchannel fabrication for biomedical or chemical analysis is an emerging technique as a fast, low-consumption, miniaturized tool in the biochemistry, analytical chemistry, microsensor, and microtechnology fields [1; 2; 3; 4]. As a typical biologically friendly material, fused quartz glass is widely used in microfluidics owing to various advantages such as low cost, high optical transparency, and structural stability [5; 6; 7]. Thus, the quartz glass microchannel manufacturing technique attracted increasing attention, especially ultraviolet (UV) laser ablation using excimer lasers (157, 193, and 248 nm) or higher-order harmonics of neodymium-doped yttrium aluminum garnet (Nd: YAG) lasers (266 and 355 nm), which are commercially available and provide large single-photon energy, great flexibility, and high manufacturing precision [8; 9]. However, fused quartz glass microchannel fabrication by UV laser is still challenging due to the brittle nature of glass and the wide band gap (9 eV) of fused quartz. Good quality of the treatment surface and sufficient etching depth are difficult to approach using traditional direct laser etching [10; 11; 12; 13]. To solve these problems, great effort was exerted in both the theoretical and experimental study of UV laser ablation. Laser-induced plasma ablation (LIPA), as a novel indirect laser etching technique, was proposed for higher etching efficiency and quality. In such processing, after the laser irradiation, the plasma vapor generated from a metal target on the bottom can effectively ablate the quartz sample's rear surface, even though the UV laser beam is highly transparent to the substrate. By means of LIPA,the quality of the etched bottom surface can be significantly improved. [PERSON] et al. presented the LIPA method for fused quartz grating manufacture using a 248 nm KrF laser. The relationship between the grating depth and the number of laser pulses was studied, showing good quality by implementing a 1.06 \(\upmu\)m grating period and a 300-nm grating depth [14]. [PERSON] et al. applied the LIPA technique with a UV pulse laser (355 nm) to fabricate quartz glass channels, showing a neat microchannel etched edge without brittle cracking or edge chipping [15]. [PERSON] et al. proposed backside wet etching using an indium-gallium cryogenic eutectic mixture as the absorption liquid, showing that the etched edge was neat, and the roughness of the bottom surface was approximately 30 nm [16]. In addition to merging the quartz in the liquid, the method of electroplating an absorbing film on the rear quartz surface was also used in LIPA. [PERSON] et al. presented an LIPA scheme using a 248 nm KrF excimer laser on a fused quartz plate with a 100 nm thick layer of silver. The etched depth of a single pulse reached 600 nm, and the roughness was as low as 2.2 nm [17]. [PERSON] et al. presented the same scheme with a UV absorbing oxide film instead of a silver coating, and single-pulse ablation depths ranging from a few to 500 nm were obtained, with a surface roughness lower than 5 nm [18]. Chemical corrosion [19] or successive electroplating [20] were also employed in LIPA treatment for the fabrication of good-quality microchannels. Nevertheless, the wet etching system is complicated, and the liquid environment is often toxic. On the other hand, the absorbing layers in the existing literature are only several hundred nanometers thick, the ablation is limited to single-pulse operation, which is insufficient for microchannel fabrication, and tedious coating and removal are necessary during the preparatory and post-processing procedures, respectively. Furthermore, many theoretical models, such as charge and kinetic exchange between the plasma and the sample surface, were proposed to describe the ablation procedure; however, these hypotheses were not validated, and the mechanism of LIPA remains unclear.