# The Effect of Laser Pulse Widths on Laser--Ag Nanoparticle Interaction: Femto- to Nanosecond Lasers
## 1 Introduction  
Silver (Ag) nanoparticles are used for a number of applications because of their electrical and biochemical properties [1; 2; 3]. Therefore, research has focused on the optical, electrical, physical, and chemical properties of Ag nanoparticles [4; 5; 6]. For example, carbon nanotubes and Ag nanoparticles have been used as additives to improve the properties of materials for transparent electrodes or solar panels, for which light transmittance and electrical conductivity are important [7; 8; 9; 10; 11]. The effect on the properties of composites of the addition of nanostructures was also examined [12]. Ag in the form of nanowires has been used to improve the light transmittance and electrical conductivity of target materials [13; 14]. Chemical- and laser-based methods for the synthesis of Ag nanostructures have been developed [15; 16; 17; 18; 19]. Among them, laser fragmentation has advanced with developments in laser sources. Laser fragmentation proceeds by irradiating a bulk metal target in a liquid with a laser pulse. This causes the ablation of the target surface, and the debris generated are degraded into nanoparticles by laser irradiation [20; 21]. Compared to conventional chemical synthesis methods, laser fragmentation reduces the risk of contamination of the particles during processing. In addition, this method generates nanoparticles with a purity greater than that of colloidal nanomaterials made by conventional chemical synthesis methods. Because laser fragmentation involves the direct laser irradiation of particles ina liquid, it has greater energy transfer efficiency than laser ablation of materials in air. The synthesis of alloy nanoparticles and the production of various 3D nanoparticles in a porous form using laser ablation and laser fragmentation in water were reported [22; 23]. Also, heat is efficiently transferred from the particles to the liquid. The mechanical pressure waves generated in the liquid also affect particle generation [24; 25]. Laser fragmentation facilitates the control of process parameters and enables the production of nanoparticles of various qualities [26]. In particular, the size of the resulting nanoparticles can be controlled by varying the laser pulse width or fluence. For example, [PERSON] et al. [27] produced nanoparticles of different sizes using femtosecond laser pulses and described the mechanism of laser fragmentation. Another research group investigated the effect on particle distribution and size of varying laser wavelengths and presented the principle of laser fragmentation [28]. It was also reported that a transferring wire target in a liquid jet can produce nanoparticles of a certain size at a high synthesis rate [29]. Irradiation by a femtosecond laser pulse width generally induces nonlinear multiphoton absorption by the nanoparticles [30]. In contrast, particle fragmentation by thermal ablation occurs mainly by melting and evaporation during irradiation by laser pulse widths in the nanosecond range [31]. Studies on the effect of the laser pulse width on laser fragmentation have mostly been conducted independently, using femtosecond, picosecond, or nanosecond pulse widths [20; 32; 33; 34; 35]. In addition, various laser fragmentation processes and metal targets can be used to produce nanoparticles. Examples of laser process parameters and nanoparticle sizes are shown in Table 1. However, these studies have several drawbacks. For example, the laser energy density was in the femtosecond or picosecond range. Also, the use of different laser pulse energies or fluences hampers the comparison of the results of different studies. [PERSON] et al. [32] assessed the effects of laser pulse energy and pulse width on nanoparticle generation for Au nanorods. They transformed Au nanorods into Au nanoparticles using femtosecond and nanosecond laser pulse widths. In this study, we produced Ag nanoparticles using laser pulse widths of femtoseconds to nanoseconds. Nanoparticle size and distribution were analyzed.