SBE Series – Small Beam Diameter

IntroductionSBE Series Beam Expander

The SBE series of beam expanders are designed for use with CO2 lasers of (relatively) small beam
diameter, between the limits of around 2mm up to 12mm, and for power levels of up to 1kW CW.
SBE units may be used to increase beam size, and reduce laser divergence accordingly, to suit ULO
Optics beam delivery equipment. A wide range of magnifications is available to enable best
performance to be obtained from the laser. The SBE series of beam expanders are of Galilean type,
with two ZnSe lenses. The lenses are made from lasergrade ZnSe and treated with ultra-low
absorption anti-reflection coatings for 10.6μm. All models are externally identical.
Technical specifications
Dimensions : See Figure 67.21.
Focus range : 2 metres to infinity, calibrated.
Cooling : Air cooled.
Maximum output dia : 25.4mm.
Input clear diameter : See Table 67.22.
Fitting : Via free-rotating coupling ring 52 x 1.5 pitch.
Beam wander during focus : <2 minutes of arc.
Available models
The available standard models range in magnification from x2 to x7, and are listed below in Table
67.22 All models are designed to eliminate spherical aberration. At full aperture the maximum
transverse ray aberration is < 10 microradians for models SBE20, 50 inclusive, and < 30 microradians
for models SBE60 and SBE70.

Focus details
The focus range is from -10 metres, through infinity, toSBE Ttable
+1.6 metres. It is factory calibrated from infinity to +2
metres focus range. Please note that the indicated
focus is geometrical, and the actual downstream beam
waist position will depend upon the parameters of the
laser beam. (See Section 67.0 and Technical Clarification
Document 4 for more details). The focus mechanism
is of the actuated-slide type, and actuation of the
focusing ring drives the output lens position in a linear,
non-rotary sense. This mechanism reduces beamwander
usually experienced with rotary focus mechanisms.

Associated equipment
The SBE series beam expanders have the standard ULO Optics ‘beam-delivery’ coupling ring.
They may be affixed to the following: OPG piping(Section 61.0), LAU25 lateral adjustment unit
(Section 72.1), LAM25 lateral adjustment module (Section 72.2). SBE series beamexpanders are used
in the laser control benches which incorporate Synrad 10W or 25W lasers and provide a complete, versatile
optical system. (Section 90.0). On request, the SBE series beamexpanders can be fitted with an optional
mechanical part affixed to the output-end of the unit. This “Alternative lock ring, P/No SBE/08X” provides
a female mounting thread, 1.5″ dia x 12TPI, at the output. This may then be used to mount any lens in an
M11-type cell, e.g. the TF series lenses, XF series lenses (Sections 20.1, 20.2) or the 11MZLF or 11HGP
series (Section 8.0).
Applications note
The SBE series beam expanders can be used to reduce beam divergence and to help achieve very high
energy densities from quite low laser power. For example, if used with a 10W Synrad laser, a model
SBE/60 plus a TF25 focusing lens, would generate an energy density of around 20kW/mm² at the
focus. Typical applications for the SBE series beam expanders with low power lasers include drilling
holes in plastics, cutting paper and card, cutting man-made fibre material and rubber, and engraving
decorative wooden plaques. In common with other beam expanders, the SBE series can provide a
long-path of consistant beam quality. They may be used in conjunction with moderate power
(several hundred watts) CO2 lasers to enable large cutting bed applications, such as the processing
of sail-cloth.

SBE beam expander diagram

 

For further information on beam expander theory, click here