Zoom Beamexpanders

 

The C-ZBE zoom beamexpander is a 3-element design using one aspheric lens. The input and output lenses are negative and the centre element positive. Using this configuration prevents the laser beam being focused internally and the consequential low power handling. The C-ZBE can therefore handling the full 500W power that the CO2mpact beam delivery is intended for. This is also the reason why the C-ZBE is not as small as other competitor models. It is 242mm long with overall diameter of 96mm.
The input and output clear apertures are both 19mm. The CO2mpact thread inserts screw into each end for coupling to other items such as beam pipe. The higher magnification ranges are intended to expand the smaller laser beams (e.g. 1 to 1.5mm) up to a suitable diameter.
In order to vary the magnification of the beamexpander while still keeping the focus at infinity, two lens elements have to be moved. In the C-ZBE these movements are not actuated by a single adjustment ring, but have been kept separate as 2 adjustment rings, labelled X and Y.

Zoom Beamexpander

Fig 1: C-ZBE zoom beamexpander. X and Y adjustments are shown and the input end is denoted by the arrow.

Use the curve in the diagram fig. 2 (or table in the appendix) to set the magnification required and the focus to infinity. If you need some positive focusing power, to correct for a diverging beam (usual case), set an operating point slightly above the line. Conversely, if you need to correct for a slight converging beam, set an operating point below the line. Adjusting the focus of a beamexpander is an empirical operation, since the output focus is dependent on the input beam – which will vary from laser to laser. The values found from fig. 2 will provide a good starting point. Note that at some magnifications (e.g. x8, x1 and ~x3) there are some restrictions on the adjustments you can make.

Zoom Beamexpander Graph

Fig 2: X and Y barrel settings required for different magnifications. Use the blue line for an infinity focus setting.

Since the adjustments X and Y of two of the lenses are independent, then it is possible for the lens mounts to collide at some settings. This does not cause the actual optics to touch, just the mount, and will not cause damage. If you feel some resistance and are not at the limits (0 or 36/0), do not force the barrels but check with fig 2 to see whether you are trying to set the beamexpander to some point on or below the straight line. For example, if you are trying to adjust the beamexpander from x7 to x4, reducing Y first will result in a collision. Simply increase X first, and then reduce Y to avoid this happening.
It is also highly recommended that when you make large adjustments, you switch off the laser. This is because you might pass through a point that focuses the beam at another optic further down the beam. Always adjust to a setting close to the infinity focus before switching the beam on and making further fine adjustments.
IMPORTANT POINTS TO REMEMBER:
1) The input end of the beamexpander is at the X adjustment ring end.

2) Always switch the laser off or block the beam, while making adjustments to the beamexpander. Start at the infinity focus setting and make fine adjustments from there.

3) The input and output beams should not be greater than about 2/3 the clear apertures. Otherwise fringing effects (rings) will be seen in the output beam (see fig. 3) and the beamexpander may get warm because some power is dumped internally.

clipped laser beam

4) Note that the adjustment rings rotate through a full 360. This means that the ‘0’ position looks the same as ‘36’ but ‘36’ is not printed on the barrel. Do make sure that when setting to 0 or 36, you do not accidentally set to the other since the output beam will be completely different. When intending to set to 0, check that the barrel can be turned in the direction of 1, 2, … Similarly, when intending to set at 36, check that the barrel will rotate in the direction 35, 34, …
5) When turning an adjustment ring, hold the beamexpander at one of the fixed ends not by the other adjustment ring.

C-ZBE-Instructions-4

 

 

 

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