New advanced materials for NLO applications employing second harmonic generation or two-photon absorption
Creators: name: Zheng, Min
Publisher: name: figshare
Year: 2022
Subjects: subject: Inorganic Chemistry
subject: FOS: Chemical sciences
subject: 30304 Physical Chemistry of Materials
subject: 30699 Physical Chemistry not elsewhere classified
subject: 30702 Radiation and Matter
subject: 30206 Solid State Chemistry
subject: 30606 Structural Chemistry and Spectroscopy
subject: 30306 Synthesis of Materials

description: <b>Nonlinear optics - introduction</b> Nonlinear optics is among the modern optics sub-disciplines that has a significant academic standing that draws fully from laser physics. Nonlinear optics research involves a variety of kinds of nonlinear phenomena that arise from the interactions between lasers and matter. The main research objective of nonlinear optics mainly involves the emerging phenomena and the new effects that occur in the interaction of high-energy lasers and materials and includes a deep knowledge of the causes, the frequency of their process, as well as exploring their possible uses for the future developments of fields. The interaction between a laser and the nonlinear optical material results in changes in optical properties of the system. In general, only light from a laser is strong enough to cause nonlinear optical phenomena. Nonlinear optical properties and related effects are widely different from those which observe every day. The way in which we see world is determined by linear optical effects such as absorption and refraction. Strength of these effects is linearly proportional on the intensity of applied light. For example, if we increase light intensity ten times, the absorbing sample will absorb ten times more photons. <b>Examples of NLO phenomena</b> For a variety of optical processes, such as SHG and 2-photon absorption (2PA), the light intensity is superlinearly proportional to the applied laser power. In 2PA, e.g., an increase in laser power of ten times results in a hundredfold more photons being absorbed by a sample. A different type of nonlinear optical process is third-harmonic generation. In third-harmonic generation, the light intensity is proportional to the cube of the applied laser power. The increased absorption of photons that comes with increasing laser power can be a boon for applications such as microscopy and sensing. However, it is also important to note that this increase in effective number of absorbed photons via NLO pathway can also be deleterious: if too many photons are absorbed, the material will overheat and its performance will significantly deteriorate. In light of this, two-photon absorption (2PA) and third harmonic generation (THG) was studied in new families of materials such as coordination polymers, metal–organic frameworks (MOFs), perovskites, and graphene. <b>Laser excitation</b> Although the discovery of the majority of optical phenomena that are nonlinear required laser radiation, certain classes of optical effects that are nonlinear were well-known long before the introduction that of the laser. The most well-known examples of these phenomena are the Pockel's effect as well as Kerr electro-optics. Theory of nonlinear optics is based on the well-understood theory of linear optics, specifically in the area of interaction between matter and light. In recent years, there has been a great deal of interest in the use of nonlinear optical materials for various applications. Nonlinear optical effects can be highly localized, making them ideal for tasks such as 3D imaging and microfabrication. In addition, they can penetrate deep into a material, making them useful for two-photon microscopy and other biological applications. <b>Potential applications</b> Nonlinear optical materials are also being investigated for potential applications in optical power limiting and all-optical signal processing. This growing interest in nonlinear optics is due, in part, to the continued development of new materials that exhibit interesting nonlinear optical properties of coordination polymers. Some of the most promising of these materials include coordination polymers, metal-organic frameworks, perovskites, nanowires, semiconductor materials and many others. A large number of compounds have been investigated for their potential use in nonlinear optical applications. In particular, dyes, both organic and organometallic, have been extensively studied. Dyes with specially designed structure have shown sizeable 2PA cross sections in broad wavelength range (especially in near-infrared spectral region), but their stability is often limited. Moreover, there are toxicity concerns associated with many dyes. <b>Materials</b> Crystal structures are not only important for understanding the bulk physical and chemical properties of a material, but also play a significant role in its optical properties. In particular, the optical nonlinearity of a material can be harnessed for various applications such as lasers, photonic crystals and optical amplifiers. In this review, we will discuss the recent progress in the nonlinear optics of metal-organic frameworks (MOFs), perovskites and other emerging materials. Metal-organic frameworks (MOFs) are a relatively new class of materials that have gained prominence in recent years for their many potential applications. One such application is as a host material for optical media, such as lasers and photonic crystals.In particular, MOFs have been shown to exhibit strong two-photon absorption (2PA) in the near-infrared region. This makes them promising candidates for use in optical devices that require high performance in the nonlinear regime.