# Laser Synthesized Graphene and Its Applications
## 1 Introduction  
The outstanding properties that graphene has demonstrated since its discovery have sparked a huge research and development effort across multiple fields, including but not limited to electronics, optics, materials science, sensing, biology, medicine, photonics, just to name a few. Such efforts have been devoted not only to exploring and understanding the properties, but also to finding new ways to synthesize, process, and deposit graphene to fit new applications. Indeed, a range of methods has been proposed, with pros and cons that make each method suitable for specific types of applications. The method that led to the discovery of graphene, mechanical exfoliation, while producing excellent pristine graphene flakes, is generally only suitable for lab-scale testing of graphene's fundamental properties [1; 2; 3]. Chemical vapor deposition (CVD) is able to produce large area graphene layers on a substrate, which can be patterned or transferred, and are suitable for optics or electronics applications [4; 5; 6; 7], but this method is limited if large quantities of material are needed for further processing. Liquid phase exfoliation, on the other hand, is able to produce large quantities of graphene flakes in organic solvents or in water with the aid of surfactants or polymers [8; 9; 10; 11]. This method has wide flexibility in terms of further processing and applications, although flakes are small if compared to those obtained by CVD.  
Oxidation of graphite is a method for dispersing graphene layers in aqueous solution with no other aid [12]. This method, however, involves the introduction of oxygen-containing functional groups, such as -OH, -COOH, or epoxy, which significantly alter the structure of graphene and thus its properties [13; 14]. This material is known as graphene oxide (GO). While some applications can benefit from GO with no further processing, other applications require GO to be reduced to reestablish the original graphene properties after the material has been processed [15]. This can be typically achieved by chemical reduction [16; 17], and the material is commonly referred to as reduced GO (rGO), to distinguish it from pristine graphene as it still contains residual functional groups.  
Laser synthesis (LS) has been brought up over the last decade as an easy, fast, and cheap alternative method for the production of graphene. This method can achieve aneffective reduction of GO as this is deposited onto a surface [14; 18; 19]. This type of rGO is commonly referred to as laser-reduced graphene (LRG). Laser synthesis was also applied on non-graphitic sources such as polymers or other natural materials, on which the action of the laser can induce a transformation into graphene [20; 21; 22; 23]. In this case, the material obtained is referred to as laser-induced graphene (LIG). Beyond providing an easy graphene synthesis method, via GO reduction or modification of other materials, LS has the intrinsic potential to create graphene patterns without using costly lithographic methods [24; 25; 26] at the resolution of the laser beam, i.e., down to 1 \(\upmu\)m, making it very appealing for a wide range of applications.  
While many other reviews have appeared on this topic (see for example Refs. [27; 28; 29; 30; 31]), most focus on a selected range of applications or sources. This paper, on the other hand, aims at reviewing synthesis methods of both LRG and LIG, their characterization, and a full spectrum of applications. Section 2 briefly discusses the fundamentals of LS, the different sources, conditions and types of laser methods, as well as the characterization of the materials. Section 3 covers the applications that have been proposed over the years for both LRG and LIG, while Section 4 provides perspectives and conclusions.