The BSL17 series are a set of compact and economical beamexpanders for use with small or medium size CO2 lasers, such as Synrad, and Coherent ‘Diamond’ lasers.

The output clear aperture is 35.0mm diameter, and models from the BSL17 range are useful for expanding the beam to a limit of about 25mm (1/e2) output diameter.

A slide-and-lock type focus mechanism eliminates rotation of the lenses and beam wander during focusing (assuming the input beam is correctly aligned).

Models from BSL17 series are intended for use up to 500W CW power.

Technical Specifications

Dimensions: See technical drawing

Construction (Mech.): Aluminium alloy, black anodised, with laser-engraved legends/focus scale.

Construction (Optical): Lasergrade ZnSe lenses, with low-absorption anti-reflection coatings for 10.6μm.BSL17-Beamexpanders-2

Focus range: -1m through infinity to +1m.

Fittings: 38.0 mm dia x 1.0 pitch male thread.

Operation: Manual slide focus, with lock screw.

Cooling: Air-cooled.

Output clear aperture: 35.0mm diameter, all models.

Transmission: >98.5% (assumes zero beam clipping).

The BSL Beam Expander Range

Part NoMag.Physical Input ApertureApprox Max Input Beam Dia.

Focusing details
The ‘infinity focus’ mark is engraved on the beamexpander body. A series of lines are engraved at 1mm intervals either side of the infinity mark. The meaning of infinity focus is that if the input beam has a flat wavefront, then the magnified output will also have a flat wavefront. A flat wavefront occurs at the beam waist.
Focus corrections by the user will be required to correct for wavefront curvature of the input beam and control the properties of the output beam.

Input aperture
Note that the mechanical input aperture is 19mm for all models. This is distinct from the optical clear aperture. The table above gives approximate maximum beam diameter (1/e2) that should enter the beamexpander.
As a general rule, for a TEM00 beam, allow 50% excess aperture over the beam diameter (at input and output). This will limit the beam clipping to 1% for a well centred beam. E.g. for the x4, although there is plenty of clear aperture at the input, the 24mm beam at the output will have the 50% clearance.

beamexpander graph


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