Mirrors or total reflectors are used in laser cavities as rear reflectors and fold mirrors, and externally as beam benders in beam delivery systems.

Silicon is the most commonly used mirror substrate; its advantages are low cost, good durability, and thermal stability.

Copper is typically used in high-power applications for its high-thermal conductivity.

Molybdenum’s extremely tough surface makes it ideal for the most demanding physical environments. Molybdenum is normally offered uncoated.

Mirrors, made from copper substrates, will withstand extremely high laser powers and industrial environments, providing diffraction limited focusing when properly mounted and aligned.

Copper mirrors are available with a higher reflectivity and durable molybdenum overcoating. This allows for the mirror’s easy cleaning.

Parabolic mirrors are designed for reflecting and focusing the laser beam through 90 degrees, or any other convenient angle.

Custom designed features, such as water cooling and non-standard mounting configurations, are available upon request.

To guarantee performance specification, all mounting surfaces must be properly conditioned, screw torques cannot exceed II-VI recommendations, and the laser source must be aligned to the parabolic axis.

As the name suggests, cylindrical mirrors are either round or rectangular objects which have cylindrically shaped surfaces. They differ from spherical mirrors in that they focus a beam to a focal line rather than a focal point.

Reflectivity is improved by applying a highly reflective coating on the optical surface. Multilayer coatings are available for various areas of the light spectrum. Cylindrical mirrors are made from Cu, Si, Ge, Al, and other metallic materials.

Applications include laser scanners, laser diode systems, spectrophotometers, projectors, and optical data storage and retrieval systems.

In many applications, spherical mirrors, cylinder mirrors, and parabolic mirrors are used to help shape the laser beam. Biconic mirrors—or the more general toroidal mirrors—can be used to combine two separate optics into one.

Biconic mirrors have two different radii on one surface. It’s possible to make a biconic mirror with spherical curves or aspheric curves, depending on the application and need to eliminate aberrations. Toroids can replace common 90° bend mirrors to recollimate a laser beam

Scanning laser systems—whether for marking, engraving, or for drilling micro via holes—all rely on galvo mirrors to precisely position the laser beam. II-VI manufactures built-to-spec galvo mirrors from mirror-grade silicon substrates. We apply our precision thin-film coatings to these substrates, producing highly efficient galvo mirrors that reflect laser light in the 1.0 to 12.0 µm range.

Ideally suited for Nd:YAG lasers (1.06µm) and CO2 lasers (9.3 to 10.6 µm), II-VI galvo mirrors are suitable for a wide range of industrial applications. And for those applications requiring a visible helium-neon or diode laser alignment beam, our dual wavelength coatings provide maximum reflectivity for the CO2 laser infrared beam while providing good reflectivity for the visible alignment beam. Our Dual Enhanced Maximum Metal Reflection (DEMMR) coating is the best choice for this application. (Details are shown in Figures 1 and 2.)

II-VI galvo mirror sizes typically range from 0.5 to 4.0 inches in diameter, based on OEM specifications.

II-VI galvo mirrors feature

• Mirror-grade silicon substrates
• Greater thermal stability than fused silica
  substrates
• Geometries built to OEM specifications
• Highly reflective coatings for Nd:YAG lasers,
  CO2 lasers, and CO2 lasers with coaxial
  helium-neon or diode laser alignment
  beams

Applications include

• Laser marking and engraving
• Laser drilling
• Laser welding
• Rapid prototyping
• Imaging and printing
• Semiconductor processing (memory repair, laser trimming)
• Remote laser welding

The II-VI Variable Radius Mirror (VRM) allows users to dynamically change their beam characteristics on the fly. By controlling the VRM’s radius of curvature with water pressure, users can adjust the laser beam divergence.

VRMs allow focus depth adjustment during material piercing; this produces optimum cutting speeds. It also allows flying optics systems manufacturers to compensate for focal length variations across the working table. This is especially important with large working tables, where laser beam divergence changes at the lens as the optical path moves across the work area.

The VRM is designed for use at near-normal angle of incidence. Many laser cutting systems use two mirrors as telescope optics. The telescope is made of one convex and one concave mirror. Replacing one of these mirrors with a VRM allows all of the benefits listed above.

Pressure Control
There are at least two ways to control the pressure in the VRM and, as a result, control the radius of the mirror surface. The key component is either a variable-speed pump or a proportional control valve. These items are driven by an amplifier. Input to the amplifier is typically a 0 to 10 volt signal. The amplifier is run open-ended or in a closed-loop system.

Custom Designs
II-VI has the engineering capability to design adaptive mirrors for any beam delivery system. Using proprietary design techniques, II-VI can accurately model the VRM shape and predict how it will deform under pressure. The mirror shape is optimized to match the pressure-radius curve defined by the customer.

Water Pressure System Example
The drawing below shows the closed-loop system that uses a pressure transducer to measure the pressure in the mirror cavity. This signal is fed back to the CNC controller.