Laser micromachining optical slits, pinholes and reticles

By: Alex Pozdin | Matt Nipper, PhD

Laser micromachining is an efficient way to manufacture light restricting components such as, apertures, optical slits, pinholes and reticles. These components are critical to the performance of many systems in the defense, life sciences, and medical industries. When performance matters, laser micromachining can deliver optimal precision outcomes. Laser Light Technologies manufactures multiple components used in high precision applications such as microscopy which uses something similar to this helium neon laser, thermal imaging, and spectroscopy.

Spectroscopy equipment utilizes entrance slits that precisely control the amount of light entering the device. The width, height, and straightness of the manufactured slit dictate the overall resolution of the device. Laser Light manufactures air slits using 302/304 grade stainless steel. The slit material has a black coating on both sides to absorb incident light and eliminate reflection and scattering from the source. One alternative to air slits are optical slits which are machined on opaquely coated, optical quality, glass disks. Typical specifications for these slits range between 5 um to 25 um with a +/-1 um tolerance. The high precision and repeatability required in the manufacturing process of optical slits, make them the perfect candidate for laser processing.

Figure 1 – Laser machined slits are inspected using a JMAR Lumina visual inspection system and packaged in our ISO Class 4 cleanroom.

Pinholes are commonly used for spatial filtering or essentially ‘cleaning’ incident light sources. The pinholes are used to correct defects in the incident light path such as aberrations, optical component contamination, or unwanted higher order modes, in the case of a laser beam. Additionally, the use of pinholes is well established in confocal microscopy where the pinhole is used to define a ‘slice’ of an image allowing the user to isolate specific regions within a 3D volume. Given the criticality of these applications, the manufacturing process must yield a consistent and reliable product. The laser machining approach is well suited to manufacture pinholes with micron level tolerances. Figure 1 shows the central portion of a pinhole with a diameter of 10 um. By implementing a roughened, opaque coating, scattering is minimized through the system. To further improve component quality, multi-level post processing is implemented to eliminate residue and remove contaminants from the central orifice area.

Figure 2 – Grid lines machined into disposable scientific microscope slide.

A client recently requested our engineers to manufacture a grid pattern into a disposable scientific glass slide package. The typical size of the grid is 1 mm x 1 mm, line width is 3 um wide and forms a grid of 100 cells with dimensions of 100 um x 100 um. The required accuracy of the grid is +/-1 um. Given the tight tolerance required in the application, we determined an excimer laser, teamed with a custom handling system, would provide the required quality along with the rapid throughput to satisfy the economics of the project.Figure 2 demonstrates the contrast produced in the machined reticle. Figure 3 is a 3D image of the machined glass reticle highlighting the controllable channel depth of the grid lines. In addition to glass, grids and patterns of lines can be also machined in other scientific-grade manufacturing materials. Figure 4 shows hexagon patterned microfluidic channels laser machined in a polycarbonate (PC) sheet. The width and depth of the channels is 12 um.

Figure 3 – 3D image of grid lines machined into glass microscope slide.
Figure 4 – Hexagonal microfluidic channels machined into polycarbonate.

Whether the application requires a slit, reticle, or pinhole, laser micromachining is capable of producing virtually any combination of features within an optical component. These components are critical to the performance of life-saving optical systems such as infrared (IR) cameras for firefighters, military night vision scopes, and other first responder imaging systems. Contact Laser Light to talk with one of our engineers about your application and how our capabilities in laser micromachining can deliver success.