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GCO-140113 Beam Expanders

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GCO-14 Beam Expanders

A beam expander is an optical system for changing the diameters of input and output beams. The product of the diameter and divergence for a laser beam remains constant between input and output. This means that, if the beam diameter increases from input, the divergence of the output will decrease. Beam expanders use this inverse-proportional relationship between the diameter and divergence to expand a laser beam, or to reduce the beam divergence. Low divergence allows for a smaller focus spot of a Gaussian beam.

In summary, beam expanders are used for fine focusing, reducing beam divergence and minimizing diffraction effect. Daheng Beam Expanders (GCO-14) are professionally designed for complicated systems and ideally used in combination with Daheng F-Theta lenses (GCO-31).

TECHNICAL NOTES

• Type of beam expander

Beam expanders are generally of a focal system; in which two groups of lenses have their focal points coincided. The front and the rear lens group are input and output lens, respectively. There are two types of beam expanders, Galilean and Keplerian, based on the input lens. Galilean beam expander is the most common type of beam expander, which is derived from Galilean telescope. It usually has one negative lens and one positive lens. The front focal point of the negative lens and the front focal point of the positive lens are coincided in front of the input lens. For lens expansion ratios <20x, the Galilean beam expander is most often used because of its simplicity, small package size and low cost. However, the Galilean beam expander is unable to accommodate spatial filters and limited to low expansion ratios. In cases where larger expansion ratio or spatial filtering is required, the Keplerian beam expanders are employed. The Keplerian beam expander has two positive lenses, which the rear focal point of the first lens is positioned at the front focal point of the second lens. In addition, spatial filtering can be instituted by placing a pinhole at the coincided focus point.

• Expansion ratio, M

The expansion ratio M is the ratio of the output beam diameter Φout to the input beam diameter Φin. It can be calculated using the focal length of theinput lens and the output lens as follows:

As mentioned above, increasing the beam diameter means decreasing the divergence of the beam by inverse proportion. So,

where θ_in is the divergence of the input beam and θ_outis the divergence of the output beam.

GCO-14 Beam Expanders

Part No.	Expansion Ratio	Wavelength	Max. Input Beam Diameter（1/e²）	Input Aperture	Outer Diameter	Length	Transmitted Wavefront	Transmission	Damage Threshold
GCO-140101	3X	355nm	6	8	40	75	<λ/4(RMS)	>98.5%	10J/cm2@10ns 10HZ 1064nm
GCO-140102	5X	355nm	4	5.5	40	95	<λ/4(RMS)	>98.5%
GCO-140103	8X	355nm	3	5	40	115	<λ/4(RMS)	>98.5%
GCO-140111	3X	532nm	8	10.5	40	75	<λ/4(RMS)	>98.5%
GCO-140112	5X	532nm	6	8	48	95	<λ/4(RMS)	>98.5%
GCO-140113	8X	532nm	4	8	48	105	<λ/4(RMS)	>98.5%
GCO-140121	3X	1064nm	8	10.5	40	75	<λ/4(RMS)	>98.5%
GCO-140122	5X	1064nm	6	8	48	95	<λ/4(RMS)	>98.5%
GCO-140123	8X	1064nm	4	5.5	48	105	<λ/4(RMS)	>98.5%