A phase-shifted fiber Bragg grating (PS-FBG) based on a microchannel was proposed and realized by combining the point-by-point scanning method with chemical etching. The PS-FBG is composed of a fiber Bragg grating (FBG) and a microchannel through the fiber core. The microchannel can introduce phase shift into the FBG. What is more important is that it exposes the fiber core to the external environment. The phase shift peak is sensitive to the liquid refractive index, and it shows a linear refractive index response wavelength and intensity sensitivity of 2.526 nm/RIU and -111 dB/RIU, respectively. Therefore, such gratings can be used as sensors or tunable filters.

In order to improve the morphology of microchannels fabricated by femtosecond laser ablation, the thermal process was introduced into the post-treatment processing. It was found that the thermal process cannot only decrease the roughness but also the width and depth of the microchannel. The change rates of width, depth, and roughness of the microchannel increase with processing temperature. When we prolong the time of constant temperature, the change rate of the width decreases at the beginning, and then it tends to be stable. However, the change rates of depth and roughness increase, and then they tend to be stable. In this Letter, we discuss the reasons of the above phenomena.

A constant elastic alloy is a widely used material with a high elastic modulus and an excellent wave velocity consistency. Different morphologies on the constant elastic alloy surface are observed through femtosecond laser irradiation. When the laser average fluence is set to 0.58 J/cm2 and 200 laser pulses, with the increasing depth of distilled water, the period of the laser-induced periodic surface structures (LIPSS) becomes shorter accordingly. The higher the ethanol concentration is, the more spot-shaped structures will be formed among the surface structures when the depth of the coverage of ethanol is 2 mm. The period of the LIPSS reaches its maximum when the concentration of ethanol is 80%.

A fused silica glass micro-channel can be formed by chemical etching after femtosecond laser irradiation, and the successful etching probability is only 48%. In order to improve the micro-channel fabrication success probability, the method of processing a high-temperature lattice by a femtosecond laser pulse train is provided. With the same pulse energy and scanning speed, the success probability can be increased to 98% by optimizing pulse delay. The enhancement is mainly caused by the nanostructure, which changes from a periodic slabs structure to some intensive and loose pore structures. In this Letter, the optimum pulse energy distribution ratio to the etching is also investigated.