## 1 Introduction  
With the development of modern science and technology, there is an urgent need in developing new techniques for micro- and nano-processing of various materials in order to create small features in large areas at high speed. Until now, various methods were explored to break the diffraction limitation, such as metalenses, e.g., Hence, micro/nanostructures were created in the interaction of laser with solid targets. For example, during the interaction of the laser with matters, nanoparticles could be formed with luminescent or plasmonic properties [1; 2; 3], especially copper plasmonic nanoparticles [4]. Among all the methods for creating small scale structures on various surfaces by lasers, decreasing the laser wavelength is still the most direct way [5; 6]. Due to the high photon energy, the damage mechanism of the extreme ultraviolet (EUV) to X-rays differs dramatically from the damage induced by longer-wavelength light, such as ultraviolet/visible/infrared light. Therefore, a novel phenomenon always occurs in the interaction of shot-wavelength light with matters. For instance, [PERSON] et al. created sub-nanometer craters on the surface of a silicon substrate by controlling strong excitations induced by a single femtosecond extreme ultraviolet pulse from a SACLA free-electron laser [7]. Generally, the thermal effect decreases the resolution of laser-processing. Capillary discharge EUV laser, because of its suitable wavelength and nanosecond duration, could be used as a proper radiation source in the study of thermal effect in the interaction process of the laser at a short wavelength with materials. After the capillary discharge EUV laser was demonstrated [8], scientists began to study the interaction of this nanosecond EUV laser with various materials. Due to the characteristic of the laser duration and the photon energy, the corresponding damage mechanism is complex including thermal and non-thermal effects. [PERSON]'s group studied the damage threshold and damage mechanism of Sc/Si multilayer mirrors exposed to a capillary discharge 46.9 nm laser, the thermal nature of the damage mechanism was presented [9]. Later, the group optimized a 2D hydrodynamic code, PULLUX, by adding new absorption and atomic physics, which enabled the simulation of the ablative properties of EUV and X-ray lasers. According to the analysis, over 85% of the ablation occurs within the first half of the laser pulse and lateral heat transport dominates at later times increasing the surface feature size future [10]. The big difference of damage mechanisms and characteristics between EUV ablation and longer-wavelength lasers ablation always present in molecular solids, because EUV photon carries enough energy to break any chemical bond in an irradiated material [11]. In this interaction process, the non-thermal effect always occurs initially and makes a major contribution to the ablation. However, for the interaction of XUV/SXR with metals which carries ample free electrons under room temperature, the ablation results may indicate a different interaction process and damage mechanism. The research on the thermal effect in the interaction of nanosecond EUV laser with metals will help to understand the damage mechanism of these short wavelength radiation sources. There are rare reports focusing on the thermal effect and melting trace in the damage induced by a 46.9 nm laser since the high photon energy is supposed to be the key role to trigger the damage on materials. In our previous work, different targets were measured by a nanosecond capillary discharge a 46.9 nm laser and melting trace was observed on copper [12; 13]. In this paper, ablation induced by a 46.9 nm laser on copper was further researched. The thermal effect and non-thermal effect in the interaction process were discussed.