Gauss-To-Top Hat Beam Shaping Lens GTH-4-2.2FA

Gauss-to-Top Hat Beam Shaping Lens is a special form lens used to distribute energy of Gaussian beam to Top Hat profile

Lens Specifications:
Material: LF5 Schott glass;
n= 1.5659 @1060 nm;
n= 1.5848 @ 546 nm;
n= 1.6192 @ 365 nm;
Clear aperture:  dia 11.0 mm;
Damage threshold (uncoated): >3J/cm2 @ 532 nm, 10 ns;
Mounted in to 1” ring holder;

 

Working distance is given by focal length of additional lens which is always needed. Top Hat appears always at focal plane of additional lens.
For instance if an additional lens f = 100 is used, Top Hat appears at 100 mm behind additional lens. So GTH-4-2.2FA could be easily put in front of objectives for example.

The distance between GTH-4-2.2FA and additional lens is not critical (up to several tens of centimeters).
The full fan angle of Top-Hat generation for GTH-4-2.2FA is 2.2 mrad. This leads to Top-Hat sizes:
– 110×110 μm for lens with f = 50 at 50 mm distance
– 220×220 μm for lens with f = 100 at 100 mm distance
– 2.2×2.2 mm for lens with f = 1000 at 1000 mm distance
– 4.4×4.4 mm for lens with f = 2000 at 2000 mm distance

 

GTH-4-2.2FA Operation Specifications

Recommended operation
wavelength range
400-1550 nm
Input beam TEM00, diameter (1/e²): 4.0 ± 0.15 mm
Achievable Top Hat size 6x diffraction limited @ 1064 nm,
12x diffraction limited @ 532 nm
Full fan angle of Top-Hat generation 2.2 mrad
Beam energy distribution efficiency > 95% of input energy within Top Hat profile
Beam homogenity ± 5 % (rel. to average intensity within Top Hat)
Lens diameter 12.0 +0.0/-0.1 mm
Lens thickness 4.0 ± 0.1 mm
Delivery

Estimated delivery time: from 4 - 5 days

Description
Code Description Price Delivery Add to cart
GTH-4-2.2FA uncoated 791 $ 5 - 6 weeks To cart
GTH-4-2.2FA-IR IR coated lens (700-1300 nm (R<1% per face)) 868 $ 4 - 5 days To cart
GTH-4-2.2FA-VIS VIS coated lens (400-700 nm (R<1% per face)) 868 $ 4 - 5 days To cart
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General Function of Top-Hat Beam Shaper GTH-4-2.2FA

 

The Top-Hat beam shaper GTH-4-2.2FA generating a square Top-Hat profile with a full fan angle of 2.2mrad. To get best results it is necessary to use a Gaussian TEM00 input beam with a diameter of 4 mm@1/e².

 

For all setups using GTH beam shaper the user have to consider that the free aperture along the total beam path have to be at least 2.2 (better 2.5) times bigger than the beam diameter @1/e2.

 

Optical Setup for Top-Hat beam shaper GTH-4-2.2FA
- Setup overview-

 

There are different possibilities to integrate the GTH-4-2.2FA beam shaper into an optical setup:
a)  Beam shaper directly in front of focusing optic/objective (Top Hat size >100μm):
      Top Hat size is determined by focal length (f) of focusing optic/objective and can be calculated as follows: 2.2*f/1000

 

b)  Beam shaper in front of beam expander (Top Hat size <100μm):
     Top Hat size is determined by numerical aperture (NA) of focused beam and can be calculated as follows:  ≈4µm/NA => ≈ 6x diffraction limited @1064 nm (12x@532 nm)

 

c)  Beam shaper within beam expander (Top Hat size <100μm):
    Top Hat size is determined by numerical aperture (NA) of focused beam and can be calculated as follows: ≈4µm/NA => ≈ 6x diffraction limited @1064 nm (12x@532 nm)

  

 Optical Setup for Top-Hat Beam Shaper GTH-4-2.2FA
- Beam shaper in front of focusing optics

 

 

 

By introducing the GTH-4-2.2FA into the beam path in front of lens/objective the initial diffraction limited Gaussian spot will be transformed into a square Top-Hat profile. 

The necessary beam diameter at the position of GTH-4-2.2FA is 4 mm@1/e2

The resulting Top-Hat size is given by: 

Top Hat Size [mm] = focal length [mm] x 2.2/1000

 

for example with f= 50mm => 110 μm.

 

 Optical Setup for Top-Hat Beam Shaper GTH-4-2.2FA
- Beam shaper in front of beam expander -

 

 

 

To realize Top Hat sizes smaller than 100μm it’s recommended to introduce the GTH-4-2.2 into the beam path in front of a beam expander. Initially the necessary input beam diameter of 4mm@1/e² is passing the GTH. Afterwards the beam is expanded and focused on working plane. The initial diffraction limited Gaussian spot at focal plane will be transformed into a square homogeneous Top-Hat profile. The resulting Top-Hat size is given by: ≈4µm/NA => ≈ 6x diffraction limited @1064 nm (12x@532 nm) NA represents the numerical aperture of focused beam and is given by: NA=beam radius@focusing optics/focal length of focusing optics.

 

Optical Setup for Top-Hat Beam Shaper GTH-4-2.2FA
- Beam Shaper Within Beam Expander -

 

 

 

A further and even more flexible possibility is to introduce GTH-4-2.2 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 GTH-4-2.2 by shifting shaper along z-axis. It’s just necessary to consider that the beam diameter at the position of GTH is 4mm@1/e². The resulting Top-Hat size is given by: ≈4µm/NA => ≈ 6x diffraction limited @1064 nm (12x@532 nm) NA represents the numerical aperture of focused beam and is given by: NA=beam radius@focusing optics/focal length of focusing optics. 
 

Homogeneous line generation with additional cylindrical lens - line thickness fixed, near diffraction limited -

 


If an additional cylindrical lens is used, one can generate homogeneous line profiles. By varying the distance l the width of line profile (short axis) can be changed from near diffraction limited size to several millimeters. We recommend the use of a cylindrical lens with a focal length of f=2.25 m.
 

 

 

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