Top Hat Beam Shaping Lens FBS

  • New Diffractive Beam Shaping Concept ! based on Fourier methods
  • Transforming Gaussian TEM00 beam into square or round homogeneous Top-Hat profile
  • Top Hat size is near diffraction limited and is given by: ~λ /NA
  • Achievable Top Hat sizes: 1 μm – 200 μm
Material Fused silica
Diameter 25.4 mm
Diameter tolerance ±0.1 mm
Input Beam

TEM00, different models for diameter@1/e²: 2.0...10.0 mm for 0.5 mm step
tolerance ±5%

Necessary Free Aperture 2.2x (or better 2.5x) beam diameter@1/e² along total beam path
Top Hat Size

1.5x diffraction limited Gaussian spot
square form (round optional)

Homogenity  +/- 2.5%
rel. to average intensity within top hat
Wavelength different models for: 1064 nm, 532 nm or 355 nm others on request
Transmission > 99% AR/AR coating
Efficiency > 95% of input energy within top hat profile
Damage Threshold  4 J/cm² @ 532 nm, 10 ns
Free Aperture 23 mm
Accessories beam expander, x/y holder

  

Ordering information for Square Top Hat Beam Shaping Lens:

FBS – A – B
A – Please indicate the wavelength needed: 1064, 532, 355, 1030, 515, 343 nm
B – Please indicate the input beam diameter needed: 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0 mm
An Example: FBS-1064-3.5 -> Square Top Hat Beam Shaping Lens, 1064 nm, 3.5 mm input beam diameter.

Ordering information for Round Top Hat Beam Shaping Lens:
FBSR – A – B
A – Please indicate the wavelength needed: 1064, 532, 355, 1030, 515, 343 nm
B – Please indicate the input beam diameter needed: 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0 mm
An Example: FBSR-532-4 -> Round Top Hat Beam Shaping lens, 532 nm, 4 mm input beam diameter

FBS - Top-Hat Fundamental Beam Mode Shaper

Without FBS Beam Shaper: Gaussian-profile at focal plane

 

 

 

With FBS Beam Shaper: Top-Hat-profile at focal plane


– FBS works together with focusing system (FS)
– Top Hat size just depends on wavelength (λ) and numerical aperture (NA) of focused beam
– Distance d between FBS and FS up to several meters

 

Intensity distribution at focal plane

Main FBS advantages:
– Smallest achievable Top-Hat size: ≈ always 1,5x of diffraction limited Gaussian-spot @ 1/e²
– Achievable Top Hat profiles: square or round
– Diffraction efficiency: > 95% of energy in Top Hat
– Homogeneity: modulation < ±2.5%
– Depth of focus: similar as for Gaussian beam
– Insensitive to misalignment, ellipticity and input diameter variation: ±5-10%

 

 Without FBS shaper: diffraction limited Gaussian profile

 

 With FBS shaper: near diffraction limited Top Hat profile

 

Optical Setup for FBS Top-Hat Beam Expander


Independent of optical setup the user has to consider that:
– The free aperture along the total beam path have to be at least 2.2x (better 2.5x) bigger than the beam diameter @ 1/ e²
– The Top Hat size is always given by: λ / NA
λ is the used wavelength;
NA is the numerical aperture of focused beam and is given by: beam radius @ focusing optic / focal length of focusing optic

There are different possibilities to integrate the FBS beam shaper into an optical setup.


1. Beam shaper directly in front of a focusing optic/objective

By introducing the FBS beam shaper into the beam path in front of a lens/objective the initial diffraction limited Gaussian spot will be transformed into a homogeneous Top-Hat profile.
When a Gaussian TEM00 input beam with a diameter of 5 mm@1/e² is used the diameter of the free aperture along the total beam path have to be at least 11 mm (better 13 mm).
If for example a wavelength with 532 nm, a Gaussian TEM00 input beam with a diameter of 5 mm@1/e² and a focusing lens with f=160 mm is used, ones will get a homogeneous Top Hat profile with a diameter of 34 μm.

2. Beam shaper in front of a beam expander

There is also the possibility to introduce the FBS beam shaper into the beam path in front of a beam expander. This leads to a higher numerical aperture of focused beam and to a smaller Top Hat profile.
Example: A Gaussian beam with a diameter of 5 mm@1/e² illuminates the FBS beam shaper and is afterwards increased by a beam expander to a beam diameter of 8 mm. With an focusing optic with f=50 mm the user can generate a Top Hat with a diameter of 7 μm. The needed free aperture increases with the expanded beam. For a beam with a diameter of 8 mm the free aperture have to be at least 18 mm.

3. Beam shaper within a beam expander

A further and even more flexible possibility is to introduce the FBS beam shaper into the beam path within a beam expander.
The user has the possibility for an easy “fine tuning” of beam diameter at the position of FBS beam shaper by shifting shaper along z-axis.

Scribing of CIGS-solar cells

– Wasted area, reducing efficiency → need of smallest scribing lines
                     – Cut quality influence efficiency → need of small HAZ, no debris, smooth edges
          – High scanning speed for high throughput → need of small pulse overlap

P1 – "Scribing“

Removal of a front contact in ZnO(1 μm)/CIGS/Mo/PI structure. Laser PL10100/SH, 10 ps, 370 mW, 100 kHz, 532 nm; scanning speed 4.3 m/s, single pass.

P3 – "Scribing“

Tilted SEM pictures of the P3 scribe in ZnO(1 μm)/CIGS/ Mo/PI structure. Laser PL10100/SH, 10 ps, 370 mW, 100 kHz, 532 nm; scanning speed 60 mm/s, single pass.

                                     Raciukaitis et. al, JLMN-Vol. 6, No. 1, 2011

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