These Galilean beam expanders incorporate the highly regarded Tropel optical designs with improved adjustability and mounting. They are ideal for applications in which a small spot must be formed at some distance from the laser, or where the collimation range must be extended for illumination, or for alignment of distant objects. Wavefront distortion of less than λ/4 guarantees a minimum focused spot size even at long ranges. The lenses are antireflection coated with magnesium fluoride optimized for 632.8 nm, yielding transmission of over 95%.

The relationship between magnification M, spot size S, range R, and depth of field Z given below, assumes a TEM₀₀ mode HeNe laser with a 0.8 mm diameter beam at 1/e² intensity level. The values in the chart are based on the relationship S = KR/M. For S expressed in millimeters and R in meters, K = 1.1 for our T81-3X. T81-10X and T81-20X and K = 1.2 for our T81-30X. The depth of field Z is defined as the distance over which the beam diameter does not exceed 1.4 times the value at the beam waist S. The values for Z are computed from the formula Z=2.5S², where S is expressed in millimeters and Z in meters. Laser beam diameters over 0.8 mm will produce diffraction rings in the focused spot due to aperturing at the output lens. For laser beams smaller than 0.8 mm diameter, the spot size will increase proportionally.

Four expansion ratios are available, 3x, 10x, 20x, and 30x, each with a means for continuous focus change. As the power increases, the beam divergence decreases proportionately, providing a greater collimation range. These beam expanders feature 1-32 mounting thread and can be conveniently attached to most HeNe lasers using  adapter. They are also equipped with precision beam centering adjustments to compensate for slight decentration of the entering laser beam (except for the T81-3X).