Efficient conversion of laser beams into a very uniform intensity top hat profile


Osela’s beam shaping technology is based on free form aspheric cylinder lens. Our in-house optical manufacturing capability is very flexible. It allows for optimization of input beams of varied sizes and efficient transformation to top hat/flat top profile of desired dimension. This optical element has the added advantage of having a very weak dependency on wavelength and can be easily integrated into existing optical systems. CV uniformity down to 1% can be readily achievable. 

Top Hat vs Gaussian

Laser beams typically have a Gaussian intensity distribution which has a high peak intensity at the center with fading edges. This profile is not advantageous for some applications. Osela’s aspheric cylinder base optics converts the optical intensity into a top hat profile, flattening the peak thereby creating a uniform profile with no losses on the edges. 

See below comparisons of a Top Hat profile having 50 um region of interest as typically used in Flow Cytometry  and other laser induced fluorescence and scatter applications.  One can clearly see that the Top Hat profile provides both high uniformity without sacrificing contained power.

Top Hat optical intensity distribution
Top Hat Profile<br >50 um ROI<br >Contained Power > 75<br >Top Hat Uniformity < 3
Gaussian optical intensity distribution
Gaussian Profile<br >50 um ROI<br >Contained Power > 75<br >Top Hat Uniformity ≈20
Low contained power Gaussian Optical Intensity Distribution
Gaussian Profile<br >50 um ROI<br >Contained Power ≈20<br >Top Hat Uniformity < 3

Key Technology Features

Achromatic: The optical element has a very weak dependency to wavelength. This allows it to be easily integrated with multi-wavelength optical systems.   

High Transmission Efficiency: Based on an all glass single element aspherical cylinder, allowing for an efficiency close to 100%. 

No High Frequency Noise: The uniformity profile created has slow variations unlike other technologies that have high ripple and high frequency noise. 

High Edge Steepness: The technology allows for the profile created to have a sharp fall off, making use of every photon. 

Flexible Dimensions: The Top Hat profiles can be designed for many different sizes and is scalable to fit your applications. Dimensions available from a few microns to multiple millimeters.

Flexible Aspect Ratio: The aspect ratio of the Top Hat axis vs the Gaussian axis is flexible and the technology comes with many options to choose from. 

No internal focusing: The technology maps a Gaussian to Top Hat profile without creating an internal focus, allowing for large input beam optical power. 

Real Technology Example

See below a real profile example of an Osela Laser projector with Top Hat profile technology. The 405nm, 300 mW laser projects a Top Hat beam at a 90 mm standoff distance.  The Top Hat has a dimension of 255 um with a Cv uniformity of 2.39% and contained energy within useful region of 78.91%.  The Gaussian dimension is 9 um.   

Actual Top Hat performance example with < 3% CV
Click to Enlarge