Why Use a Flat Top Beam Shaper?
A beam shaper top hat is a diffractive optical element (DOE) that alters the phase of an incoming Gaussian beam into a flat top-shaped energy distribution. This article will discuss the beam shaper top hat’s qualities and when it is advised to use such a device.
Introduction to beam shaping optics
Nowadays, the advancements in laser manufacturing and power availability enable improvements in many laser-based applications. Shaping the laser beam into various energy distributions tailors the output beam for specific treatments and processes, allowing higher throughput and quality in laser processing.
When referring to beam shaping optics, there are several different methods available in the market, ranging from simple to complex. A simple coarse glass can diffuse the light passing through it to produce a homogenized beam. Complex optical modules composed of multiple lenses and other optical elements also perform this function.
This article will focus on one laser beam shaping method which is compact, cost effective, and most importantly provides the most accurate beam shaping results — the diffractive beam shaper.
Generating flat top beam profile with a diffractive beam shaper
A diffractive beam shaper is an analytical optical component. In other words, it performs a well defined optical function whose output is a known continuous phase profile, without phase randomization. This device is a flat, window-like element, with a unique computer optimized pattern etched into its surface in micron scale steps. When illuminated, this etched pattern creates phase delays to portions of the light which pass through the element. When designed correctly for a specific input beam, these phase delays can be controlled to ultimately generate an output image with almost any desired shape and size characteristics. Moreover, the generated beam shaper light has a very homogeneous and uniform energy distribution within its shape, with sharp edges separating the inside area containing the energy and the outside area with no energy.
When focused, this type of energy distribution can provide a competitive advantage to many laser system integrators, specifically in material processing applications, such as laser micro-machining, accurate scribing of solar panels, etc.
Why is beam shaping required for the laser beam?
Although power is becoming more and more available, it is still one of the most expensive components of the laser-based system throughout its entire equipment lifetime. Therefore, utilizing the available power in the most optimized manner is advised. This is a major advantage of using the diffractive flat top beam shaper.
The shaped laser beam is, in most cases, custom designed for a specific system and set of process parameters. The beam is typically defined to create an output that is flat, just slightly above the required process threshold to avoid any unnecessary energy waste. The output beam shape and size will also be adjusted to the required process parameters to enable maximum processing efficiency. This increases the equipment threshold as compared to using a non-shaped (Gaussian) beam.
In addition, thanks to the zero angular tolerance of the DOE manufacturing process, integrating a beam shaper top hat into a system guarantees process repeatability of multiple similarly designed systems. This repeatability is no dependent on the processed area of the laser pulse energy, unlike the case with a typical Gaussian beam.
When is using a beam shaper laser advised?
Not every system can use a beam shaper top hat.
The beam shaper top hat optical component, due to its unique qualities, is normally integrated into high value systems that require a very accurate treatment, especially in cases where multiple systems need to operate in the same manner. A common use for the top hat is in systems where allowing energy flow outside the desired area would cause damage.
There are some hard requirements for using a beam shaper top hat, such as: the input must be a highly coherent single mode beam with M2 value < 1.5, or a required ratio between the beam diameter and the optics clear aperture.
In other cases, where shaping is desired but the input beam is a multimode beam, other beam shapers such as a diffractive diffuser or a broadband diffuser can be used. Both options provide excellent shaping qualities and increased system throughput, and are good choices when a large area needs to be treated, and not a focused one.
Holo/Or develops, designs and manufactures diffractive optical elements (DOEs) and micro-optical elements for any wavelength, from DUV to far IV, as well as software/automation solutions for the design.
For more information, contact Holo/Or.