What is a panel light diffuser?

February 27, 2023

An optical diffuser is an optical element that disperses the optical power of an incoming beam, that is, spreads the light energy of the beam profile, making the energy envelope smoother than the original incoming beam.

There are many types of optical diffusers, including holographic optical elements and perfectly reflective diffusers, but in this article, we will focus on the application of optical diffusers in high power laser systems, namely diffractive diffusers and microlens diffusers Applications.

Some FAQs about Optical Diffusers

What is an Optical Diffuser?

An optical diffuser is a component that homogenizes and smoothes the profile of a beam of light. Some optical diffusers (diffractive diffusers) work in transmission, while others (microlens diffusers) work in reflection.

How are optical diffusers designed?

The design of the optical diffuser is based on the desired angle, intensity curve and shape. Diffractive optical diffusers are optimized for a single wavelength with extremely high angular accuracy, while refractive microlens diffusers work over the entire transparency spectrum of their material but with less angular accuracy.

How are optical diffusers produced?

There are many methods to produce high-power optical diffusers, including methods based on semiconductor lithography and etching, and laser-based ablation or laser-assisted etching methods.

Application of Optical Diffuser in High Power Laser System

There are many applications for optical diffusers in high power laser systems, some common applications include.

Skin cosmetic laser treatments, including tattoo removal. Typically, the lasers in such systems have an uneven intensity profile, potentially damaging hot spots on the patient's skin. This is where an optical diffuser is used and shaped into a smooth spot of the right size for optimal treatment results.

Laser welding, laser cladding and laser annealing using large core (>100um) multimode fiber lasers. In such applications, where multi-kilowatt beams are often used, large diameters (>10mm) are required after fiber laser collimation to avoid damage to the optical system. These beams can be shaped by optical diffusers, due to their highly multimode nature and lack of speckle, to achieve rectangular or linear profiles suitable for certain industrial processes.

Laser-based deep-UV lithography, typically using very high M2 excimer lasers. Such lasers tend to have non-uniform or unstable profiles, and a common way to deal with this is through the use of optical diffusers to shape and homogenize the beam. In this application, diffractive diffusers are preferred in most cases because the angles are often very small and absolute angular accuracy is often required.

Optical Diffuser Design

The design of a diffractive optical diffuser takes into account the desired shape and intensity profile, as well as the wavelength, to be produced by the diffuser.

These design parameters are fed into an iterative Fourier transform analysis (IFTA) algorithm, which optimizes the phase of the simulated diffuser to minimize deviation from the desired profile. Diffraction designs are composed of binary levels, usually between 2-16 levels. Due to its multi-level, high-efficiency design, this optimization often results in optical vortices in the phase, making production challenging and requiring high-precision alignment.

Microlens diffusers, often called refractive diffusers, are designed analytically by defining the pitch and sag of the lenses. For circular diffusion, some randomization factor (cell shape or lens position) is used to break the symmetry of the lens and achieve the shape.

In more complex refractive optical diffusers, other types of phase randomization are often added to the lens surfaces to improve uniformity and reduce order artifacts produced by microlens spacing, such as Holo/Or's broadband diffusers.

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