A “laser” (Light Amplification by Stimulated Emission of Radiation) is a tool which utilizes an initial input of light or energy to generate a narrow, intense, and uniform beam of light. Differing conditions in the construction of the laser apparatus impact the features of this beam including its specific wavelength, intensity, color, focal length, diameter, and diffraction. While each component of the laser plays a role in these variations and certainly deserves a more in-depth look, the impact of the laser optical aperture, used outside the laser cavity, will be our focus here.
What is Aperture?
The term “aperture” simply refers to a structure that restricts/channels the passage of light.1 It is perhaps most commonly associated with a basic camera where it controls the flow of light into the lens when taking a photograph. In a laser, however, aperture typically refers to the area from which the generated beam of light exits the apparatus. Aperture, therefore, can refer to an opening affecting the flow of light into or out of a system.
Due to its light channeling nature, the aperture has a tremendous impact on the beam in laser system. While much of the beam’s wavelength characteristics are based on internal variables, there are several features correlated with aperture size. For one, light inherently scatters, or diffracts, when hitting the aperture. The degree to which diffraction will occur is directly proportional to the aperture size: the beam wavelength / aperture size = degree of diffraction. Diffraction in turn affects how quickly the beam will spread out.2 Aperture also impacts the focal length of the laser beam (i.e.—how far away from the apparatus the beam will hit its focal point) and perhaps most obviously, the diameter of the beam upon exit. 3,4
Importance of Aperture in Laser Function
In light of these many impacts, ability to control aperture size is paramount to setting up a successful laser system, particularly one well suited to the context of a laser’s intended use. In some cases, a single aperture size is appropriate and will generate a beam of the correct width, focal length, intensity, etc. to accommodate the task at hand. In other cases, however, an adjustable aperture is needed to either determine by trial and error the most appropriate opening size, or perhaps accommodate the need for differing focal points and diffusion rates. Use of iris diaphragms like those sold by EKSMA Optics allow for such adjustments and even come with a choice of aperture material to accommodate differing degrees of laser intensity.
Like all components of laser systems, optical aperture plays a big role in the function of the light beam used. By altering the size of the opening, a beam’s focus range, size, diffraction rate, and more are impacted. The customizable nature of a laser, particularly when an adjustable iris diaphragm is added, has allowed these tools to be useful across many disciplines and continues to encourage new and innovative applications.