## 1 Introduction  
Nanoparticles are applied in optoelectronics (as catalysts) and drug delivery systems because of their unique optical and chemical properties. Instead of nanoparticles composed of single elements; metal nanoparticle compositions are now being studied. Bimetallic particles may exhibit superior properties [1; 2; 3; 4; 5]. For nanoparticle-mediated photothermal treatment, Ag or Au nanoparticles have been preferred, but their material properties limit efficacy [6]. Optical properties and photothermal stability are improved if Ag or Au is combined with Pd [7]. [PERSON] et al. studied the light-to-heat conversion ability of AuPd nanoparticles [8]. In this study, it was found that Pd can act as an important element to increase the light-to-heat conversion efficiency depending on the bond type and amount. This means that the alloy containing the element Pd can be more effective in photothermal treatment. In addition, changes in the stability of nanoparticles with heat can be a problem in nanoparticle applications. [PERSON] et al. confirmed that nano-octopods alloyed with Pd have improved stability compared to nanoparticles without Pd added at higher temperatures [9]. The AuPd heterometallic bond greatly improves catalytic and filtration performance. Heterogeneous bimetal nanoparticles may have the same structure as a metal alloy, metallic compound, or solid solution [10]. To date, most heterogeneous nanoparticles have been chemically synthesized, including via chemical reduction of an aqueous solution containing a surfactant. Metal shapes and sizes are determined by the surfactant and energy applied (ultrasonic waves or microwaves that induce nanoparticles in an apparatus that resembles a microwave oven) [11; 12; 13; 14]. Compared to conventional heating, wave energy improves the energy transfer rate; direct heating enhances synthetic efficiency [15]. However, secondary liquid heating can be problematic, although test reproducibility is high. The synthesis of metal nanoparticles in liquid via pulsed laser energy (a photochemical reaction) has been explored for decades [16; 17; 18; 19; 20; 21]. It is possible to control the light wavelength and pulse width, and thus nanoparticle generation. Nanoparticles are produced at room temperature and are free of surfactant contamination. Nanoparticles several nm in size are easily generated. Complex nanoparticles of various shapes and sizes can be created from simple nanoparticles. The laser wavelength can range from the ultraviolet to the near-infrared, and the pulse width from femtoseconds to nanoseconds [22; 23; 24]. Nanoparticle generation via laser irradiation in liquid is classified as laser ablation in liquid (LAL) [25; 26; 27; 28; 29], laser fragmentation in liquid (LFL) [30], or laser melting in liquid (LML) [31; 32] as shown in Figure 1. These methods can be further divided into top-down procedures that fracture a material when generating nanoparticles, and bottom-up approaches that incorporate an elemental material into new nanoparticles. Both mechanisms can be applied simultaneously. The principle underlying nanoparticle fabrication through ablation of a material using a focused high-energy laser is as follows. When the laser irradiates the material surface in liquid, nanoparticles are generated via near-field ablation, coulomb explosions, and photothermal ablation [33; 34; 35; 36]. The nanoparticles thus created are then subject to the secondary effects of laser pulses, such as liquid shock waves. Typically, particles separated from the bulk material are fragmented by cavitation bubbles generated via LAL. In addition, the particles may repeatedly agglomerate to form homogeneous nanoparticles of various sizes [23; 24]. Initially, nanoparticles are generated by irradiating a bulk metal. This is followed by a growth phase wherein the initial nanoparticles encounter laser pulses. Liquids can contain a variety of metal ions. When ablating a solid target, the ablation mechanism varies by the pulse width.