Using Top Hat Beam Shaper to Cut Film
The rising demand for Organic Light Emitting Diode (OLED) screens resulted in a search for better laser-based film cutting solutions that require higher power and better processing quality.
One of the problems that manufacturers are currently facing is reducing the Heat-Affected Zone (HAZ) next to the edges of the cut. One solution to mitigate this problem is the use of short-pulsed CO2 lasers.
Another possible solution is using a Top Hat beam shaper to reduce the width of the edges of the laser-treated area, thus reducing the HAZ.
What is a Top Hat beam shaper?
A Top-Hat beam shaper is a Diffractive Optical Element (DOE) designed to change the energy distribution of a Gaussian single mode beam to a more desirable distribution. These DOEs are mainly used to shape the output beam into a flat, uniform distribution with sharp edges. Top Hat beam shaping can create spots with various shapes, including linear, round, square or a rectangular, all with flat top intensity. Other DOEs with customized shapes can also be designed and manufactured.
Compared to a Gaussian distribution with the same threshold area size, the edges of the Top-Hat beam profile are much sharper. This means that a smaller area will be exposed to the beam and HAZ should therefore be reduced.
Since film cutting is a threshold processes, it is characterized by a certain threshold laser energy density that must be achieved for a certain area to be processed. For such processes, a flat top energy distribution has advantages that make it highly desirable.
Unlike the Gaussian beam profile of single mode beams, where the width of the Gaussian spot (above the process threshold) is directly proportional to the energy, a Top Hat energy profile is characterized by having almost no dependence between the pulse energy and spot size above the threshold. This means that the same results can be achieved by using lasers with lower maximum pulse energy, compared to an equivalent width cut done by a Gaussian energy profile. Lower energy means that there is much less energy in the beam edges, and consequently less HAZ when using a Top Hat laser beam shaper to get a flat top beam.
Profile of Top Hat vs Gaussian Shape
Integration of diffractive Top Hat beam shapers into laser film cutting
Diffractive Top Hat beam shapers are often easy to integrate into existing laser machines for film cutting applications. Such machines often create the cut path by either scanning the head with a stage or by using a galvo and F-theta setup to steer the beam. In both cases, getting a Top Hat beam laser beam profile using one of Holo/Or’s DOEs is simple, as you only need to integrate a single, flat, window- like component into the existing optical path. This makes integration straightforward.
The main requirements for successful use of the Top Hat laser shaper are:
- Single mode input beam, M2 < 1.3 (typical of most CO2 lasers)
- Beam diameter ±5% of designed beam shaper input diameter
- Clear aperture of scanner, lens and all other optics at least 2X the input beam size
To further aid integration, Holo/Or has written an installation guide and application notes.
For more information, contact Holo/Or.
(The original version of this item is a post on the Holo/Or website.)