Top Hat Beam Shaping Lens FBS

FBS series Top Hat beam shapers are designed for generation of round or rectangular/square Top Hat profiles. All beam shapers are so called focal beam shapers and generate the Top Hat profile in focal plane of nearly any focusing optics.

 

FBS series can be used to generate Top Hats sizes which are typically smaller than 100µm. The Top Hat size can be easily scaled by using additional different focusing optics (respectively the focal length).

 

FBS beam shaper can be combined with any objective or F-Theta lens. FBS can be included at nearly any position into the beam path (even in front of or within a beam expander/telescope).

 

The diameter of Top Hat in the focal plane will be 1.5 times larger than the diffraction limited Gaussian focus and is approximately given by 2*λ*f/d or λ/NA with the numerical aperture (NA) of the focused beam. FBSR elements need to be matched to the laser wavelength (λ) and the (input) beam diameter (d).

Ordering information for Square Top Hat Beam Shaping Lens:

FBS2 – 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: FBS2-1064-3.5 -> 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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