The process of modifying the wavefronts or shape of a laser beam is known as laser beam shaping. But why do we need to shape the laser beams? To understand the necessity of laser beam shaping, first, we have to understand the characteristics of the Gaussian beam profile. Most natural laser beams exhibit a Gaussian distribution pattern. In this beam profile pattern, the value of irradiance level reaches its maximum value at the center and then decays slowly toward the edges. The absence of sharp edges theoretically means that the value of irradiance level never becomes zero. Therefore, in this beam pattern, a substantial amount of light energy does not exploited. To overcome this issue, we need to shape a laser beam in a way that its beam profile achieves sharp edges and uniform irradiance level. This beam shaping is really important for various industrial and medical applications.
Types of Laser Beam Shapers
To change the wavefront of a laser beam, we need a unique phase element known as a laser beam shaper. There are various types of laser beam shapers, such as
- Top Hat Beam Shapers,
- Diffractive Diffusers,
- Micro-lens Arrays, and
- Broadband Diffusers
The optical principle that Top Hat laser beam shapers and Diffractive diffusers use to shape the laser beams is the diffractive principle. Top Hat laser beam shapers are basically DOEs or diffractive optical elements that are designed to generate a desired spot geometry and intensity profile by exploiting the wave nature of the input beam. When it comes to shaping single-mode laser beams of known diameter, diffractive Top Hat beam shapers can be used to achieve excellent sharpness and uniformity with a smooth phase and no speckle . For multimode cases, The shaping solution is diffractive diffusers, that overlay the beam multiple times on itself, enabling a smooth envelope but randomizing the phase (which may result in speckle for more coherent lasers).
Micro-lens arrays and broadband diffusers follow the principle of refraction to shape the laser beams in a manner similar to diffractive diffusers, i.e by scrambling the phase . Micro-lens arrays are efficient in shaping polychromatic beams and obtaining irradiance uniformity within a particular area. However, the issue with these beam shapers is the presence of order artifacts inside the shape and the limits to shaping (only rectangles, lines and hexagons are possible). Whereas, broadband diffusers can help to obtain fewer artifacts and more homogeneous irradiance as well as shape the input beams in different geometrical shapes, including circles, squares, and lines.
Applications Of Laser Beam Shapers
Laser beam shapers have plenty of applications in the industrial field, including welding, laser scribing, and other material processing processes. To obtain a uniform and confined irradiance spot, laser beam shapers are essential. Beam shapers are also efficient for cutting glass and metals in ablation processes.
Apart from industrial applications, beam shapers have noteworthy applications in the medical field, including aesthetic treatments, such as tattoo removal, skin resurfacing, surgical lasers, and body contouring. In laser projection applications, beam shapers help to confirm micro-display uniformity.
