**1. Introduction**

Ophthalmology has faced substantial changes by the advances in medical technology. These advances include developments in diagnostic and therapeutic strategies. One of the important advances of recent years, which has changed the field of ophthalmology, is the laser. After the development of the early solid-state lasers, FSL was developed as a near-infrared laser with ultra-short pulse duration, which enabled safety, precision, and predictability of ophthalmic surgeries and improved the postoperative outcome of patients. It has also been used for the fabrication of several optic devices, which helped to improve the precision of diagnosis and treatment in the field of ophthalmology. The ongoing advances in FSL technology since its introduction are making the newer machines with better quality, stability, and fewer complications. Therefore, it is suggested that researchers and clinicians keep themselves updated about the advances in FSL technology and make use of the updated technologies to benefit from its advantages.

Nano/micro-devices have diverse applications in optics, nanophotonics, Opto-electronics, and biomedical engineering. As the transparent layers of the eye do not absorb electromagnetic radiation, light does not alter them, but the light energy is absorbed by them, causing focal tissue disruption. Laser systems with different wavelengths have been developed based on these principles with several applications in ophthalmology. The femtosecond laser (FSL) is a near-infrared laser with a wavelength of 1053 nm and a diameter of 0.001 mm. The term "femtosecond" refers to the pulse duration of one billionth of a second, fired in the nanosecond domain. This ultra-short pulse duration allows for smaller shock waves, focus to a 3-μm spot, no heat development, and less damage to the adjacent and superficial tissue (collateral damage) [1].

FSL works by the production of a different tissue interaction, known as photodisruption. Within the cutting plane, micro-cavitation bubbles are formed discretely. Non-linear absorption of laser energy is obtained by using many photons at the same place and time. This multiphoton effect causes the tissue to absorb energy as high as it results in optical breakdown. This process of photodisruption creates plasma, acoustic shockwave, thermal energy, and cavitation bubble, which expands at supersonic speed, slows down, and then implodes and eventually forms a gas bubble composed of carbon dioxide, water, nitrogen, and other elements. This will break the limitations of traditional fabrication methods, which results in two–threefold better precision than cell surgery using continuous-wave irradiation [2]. In addition, the quality of fabrication is also improved in FSL, due to the non-equilibrium and non-thermal absorption phase transitions, resulting in reduced heat-affected zones, cracks, and recast layers. Furthermore, FSL requires no mask, vacuum, or reactive gas environment. These characteristics make FSL applicable in different manufacturing processes, such as telecommunications technology, biotechnology, pharmaceuticals, aerospace, and environmental industries. The non-linear and material-independent absorption of femtosecond lasers makes them ideal for creating complex 3D structures in composite substrates with nanometer-scale precision [3].

Modern laser technology is rapidly improving in terms of resolution, productivity, and materials. Using smart materials to create three-dimensional (3D) microactuators and microrobots is a newfound application. With femtosecond laser processing, optical devices can be seamlessly integrated with other components, enabling new applications such as 3D microfluidic, optofluidic, and electro-optic devices.

We discuss mechanisms and methods for femtosecond laser, including digital micromirror devices, different processes, and interferences. Microlens arrays, micro/ nanocrystals, photonic crystals, and optical fibers all have applications in the production of optical devices. Using femtosecond lasers, one may create scalable metamaterials with multiscale diameters from tens of nanometers to centimeters. Improved methods may result from the availability of effective femtosecond laser surgical equipment for any refractive surgery processes, Photo disruptive ultrasonic lens surgery as a combo approach in any medium to altering the power of the intraocular lens (IOL) postoperatively. The huge potential of femtosecond laser processing in fields such as machinery, electronics, biosensors and biomotors, physics, and chemistry requires more research.
