Ronar-Smith® Bessel Lenses

Bessel lenses are used in deep laser cutting applications. Bessel beam, which has a small focusing spot size and long focus depth is generated by allowing laser light to pass through a combination of the axicon lens and focusing lens. The tunability of depth of focus of the output beam by adjusting the size of the input beam diameter is the most attractive feature of this Bessel beam optical system.

Customization

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Part No	Wavelength (nm)	FFL (mm)	WD (mm)	Max Input Beam Dia (mm)	Max Cutting Length (mm)	Spot Size Range (µm)	Total Length (mm)
BESL-355-10-D10	355	249.04	10.70	10	1.5	< 1	376.00
BESL-532-10-D10	532	212.70	11.86	10	1.5	< 1	202.84
BESL-1064-D10-T2	1064	-	10.80	10	6.0	-	238.00
BESL-1064-D20-T12	1064	330.05	15.00	20	12.0	< 5	315.05

No.	Pulse Energy	No. of Pulse	Frequency	Spot Distance	Focusing Range	Cutting Result	Splinter Effect
1	620μJ	6	50k	5	5.6mm	Smooth	Easy to Break
2	714μJ	6	50k	3	5.8mm	Smooth	Easy to Break
3	714μJ	6	50k	4	5.8mm	Smooth	Easy to Break
4	714μJ	6	50k	5	5.8mm	Smooth	Easy to Break
5	810μJ	6	50k	3	6mm	Smooth	Easy to Break
6	810μJ	6	50k	4	6mm	Smooth	Easy to Break
7	810μJ	6	50k	5	6mm	Smooth	Easy to Break

Laser Processing

Bessel Lens for Laser Cutting & Deep Hole Drilling Application Note

Introduction

A bessel lens consists of axicon lenses and two sets of focusing lenses. The collimated light passes through the axicon lens to form the bessel beam, which is non-diffractive and has concentric rings each having the same power as one another. The ring diameter changes with the change in focal depth, but the ring thickness remains the same. This type of ring-focused beam is much more suitable for material processing applications with a diameter-to-long depth ratio.

Figure 1 shows the basic optical design principle of the bessel lens. The whole lens is composed of a set of axicon lenses and two groups of focusing lenses.

Working Principle

The generation of a bessel beam through an axicon lens produces a transverse light energy distribution with no diffraction characteristics. At the location of beam convergence, a longer diffraction-free region is produced (Figure 2), where the beam energy density does not change with the propagation distance. Combining the axicon lens with a focusing lens (Figure 3), a high-energy Bessel beam can be achieved (Figure 4).

The beauty of the bessel beam optical system lies in the tunability of the output beam depth of focus (DOF) by simply adjusting the size of the input beam diameter. With an approximal linear relation between the input beam diameter and the output beam DOF (Figure 5), our Bessel lens is the solution to your needs.

Figure 2. Bessel Beam Regional Distribution

Figure 3. Bessel Beam Optical System Layout

Figure 4. (a) Simulation Plot of Energy Density Distribution in Bessel Zone and
(b) Beam Profile Analysis (FWHM) of Output Beam

Figure 5. (a) Plot of Longitudinal Section vs. DoF, and
(b) Plot of Output Beam Size (FWHM) vs. Input Beam Diameter

Field of Application

Bessel lenses are suited for laser cutting and deep hole drilling for modern industrial applications, with a requirement for versatility, high efficiency, and precision material processing. These lenses are a unique solution to a specialized field of laser process technology that requires small focusing spot size and long focus depth. Integrating with a laser cutting system, it generates high localization and stringent directional control of the focused beam, providing flexibility in cutting steel, glass, and other materials. An in-build compensation mechanism allows for adjustment by customers to meet their desired optical performance.