Beam Expander Application Note

Author: Neo – Principle Engineer, Christopher Lee – R&D Manager

Laser Optics Zoom Beam Expanders
BXZ Series

The Ronar-Smith® Beam Expander demands the highest beam broadening and collimation quality without compromising on the expanded beam quality. We value safety as much as we do quality, and that is why we ensure all our beam expanders are subjected to rigorous testing prior to market sales. Our beam expanders are telescopic by nature and require a collimated beam input while delivering an expanded collimated beam at the output.

What makes our beam expander products unique is the broad wavelength input we carry and the customization services we provide. Our product customization services are of great value for customers who need specific requirements in their industrial and production lines. The parameters that we are able to provide with customization include wavelength-specific filtering, anti-reflection coating, magnification factor selection, input/output clear aperture, and maximum beam intensity.

We provide ready-stock Ronar-Smith® beam expanders in three configurations: fixed (BEX series), zoom (BXZ series), and motorized zoom (BXZ-MOT series).

Working Principles

Fixed Beam Expander (BEX Series)

Beam Expander 1
Figure 1. Fixed Beam Expander

Beam expanders in laser system development are utilized for calibrating various elements. The diameter of the laser beam at the laser system output is adapted to the required diameter at the input of the objective lens. The beam expander is also primarily used in laser-material processes.

Fixed beam expanders are also designed for specific beam expansion applications such as laser engraving. They also feature anti-reflection coatings and high transmissivity to maximize the efficiency of the beam expansion and reduce losses. The disadvantage lies in the fixed magnification factor and applications that require tuning of the output beam size are unable to perform.

Zoom Beam Expander (BXZ and BXZ-MOT Series)

Beam Expander 3
Figure 2. Zoom Beam Expander

The zoom beam expander accounts for the shortfall of the fixed beam expander by allowing the user to tune either manually or automatically (motorized) to the required magnification factor, depending on various processes that are required. These beam expanders are also designed for high-power applications where magnification adjustments may be required.

The concept of the zoom beam expander works on the internal translation stages and focusing mechanisms to adjust and account for the changes in magnification continuously. It also takes laser divergence into consideration and performs relative adjustments without affecting the overall housing length.

Versatile Beam Expansion: From Tunable to Automation

The function of a beam expander is to take an input collimated light and expand (or reduce) its output beam diameter. For example, the BXZ-9.4-0.5-3X zoom beam expander allows for the laser output beam diameter to be magnified by 0.5 to 3 times its input beam diameter.

Operation Principle

Beam expanders primarily make use of two types of optical designs, namely Keplerian and Galilean. Keplerian design involves the use of a positive lens pair. While the Galilean design makes use of a negative and a positive lens pair. For our RONAR-SMITH® zoom beam expanders (BXZ series), the Galilean design is adopted. Galilean designs are generally shorter than Keplerian ones with the same magnification level.
Such designs, without tight focusing, prevent the ionisation of air when high energy lasers are used.

Keplerian beam expander and Galilean beam expander
Figure 1. Design of beam expander.

The key specifications of the different zoom beam expanders are listed below. Compared to similar products in the market, we offer versatile tunability and automatic control at different laser wavelengths.

Wavelength257nm, 355nm, 532nm,
1064nm, 1550nm, 1940nm,
2.800um, 9.4um, 10.6um
Magnification0.25—10X
Divergence
adjustability
Yes
Angle of incidence0 ± 0.06°
Pointing stability< 1.0 mrad
Other specificationsRefer to catalog
Table 1. Key specifications of the zoom beam expander

With in-house design capability, a typical zoom beam expander outline is shown in Figure 2. All designs come with a detailed specification table and operation manual.

Manual Zoom Beam Expander Outline
Figure 2. Outline of a typical zoom beam expander.

Applications

(a) Automatic Tunable Beam Expander

Following the global trend in automation, we came up with a new series of automatic beam expanders. The unique design of an integrated printed circuit board provides an integrated communication port, a memory-based calibration function, and a high accuracy of 10um.

Auto Motorized Zoom Beam Expander and Control Board
Figure 3. Automatic beam expander and in-house
developed control board

(b) Reflective Design

To minimize the tight focusing effect in the Keplerian design, we came up with new modules based on reflective focusing optics. It could be used as a stand-alone module, or integrated with other transmission-based beam expanders.

Design-of-Reflective-Beam-Expander
Figure 4. Design of reflective beam expander

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