In cylinder lens manufacturing, surface roughness, as a key quality indicator, plays a decisive role in controlling beam quality. Its influencing mechanisms involve multiple aspects, including light scattering, wavefront distortion, and energy loss, requiring a comprehensive analysis from three perspectives: optical principles, processing technology, and system matching.
Light scattering caused by surface roughness is the primary factor affecting beam quality. Microscopic undulations on the cylinder lens surface disrupt the ideal smooth reflective or refractive interface, causing the incident light to deflect in unintended directions. This scattering can be categorized as specular scattering and diffuse scattering. The former is caused by periodic ripples, forming diffraction fringes with specific angles; the latter arises from irregular microscopic protrusions, causing the beam energy to spread in multiple directions. In high-power laser applications, scattered light can cause localized overheating or disrupt the energy distribution in the target area. In precision imaging systems, scattered noise can significantly reduce the signal-to-noise ratio and even obscure the valid signal.
Wavefront distortion is another key influence of surface roughness on beam quality. Cylinder lenses are commonly used to convert point sources into line sources or to focus beams in one dimension. When surface roughness exceeds wavelength levels, optical path differences introduce phase errors into the wavefront, leading to a widened focus line and uneven energy distribution. For example, in laser cutting systems, wavefront distortion can cause the slit width to fluctuate beyond the permitted range; in optical coherence tomography, it can result in a reduction in axial resolution. This distortion is closely related to the spatial frequency of the roughness: low-frequency roughness primarily causes astigmatism, while high-frequency roughness leads to speckle noise.
The relationship between energy loss mechanisms and surface roughness is manifested in the dual effects of absorption and scattering. Cylinder lens materials inherently absorb specific wavelengths, and surface roughness further increases scattering losses in the optical path. In the ultraviolet or deep ultraviolet wavelengths, even micron-level roughness can result in several times the energy attenuation. Furthermore, rough surfaces easily absorb contaminants, forming a composite absorption layer that exacerbates energy loss. In laser processing or optical communications, this loss can directly limit system efficiency and requires ultra-smoothing machining techniques to control.
The machining process and surface roughness control are closely coupled. In traditional grinding and polishing processes, abrasive particle size, pressure, and rotational speed directly influence the surface microtopography. For example, using W28 (approximately 28μm particle size) alumina abrasive may leave periodic scratches on the cylinder lens surface. However, chemical mechanical polishing (CMP) technology, through the synergistic effect of a soft polishing pad and chemical etching, can achieve subnanometer roughness. In the compression molding process, the mold surface quality directly determines the lens roughness, and mold defects must be eliminated through precision coating and heat treatment.
System compatibility requires dynamic adaptation of the cylinder lens surface roughness to the beam parameters. For a Gaussian beam, if the scattering angle caused by roughness is greater than the beam divergence angle, scattered light may enter the main optical path, forming a stray light background. For a flat-top beam, the edge energy attenuation caused by roughness can disrupt light intensity uniformity. In adaptive optics systems, wavefront sensors are required to monitor the distortion caused by roughness in real time and drive deformable mirrors to compensate. This places strict limits on the spatial frequency distribution of roughness.
Detection technology is a key support for controlling cylinder lens surface roughness. Interferometers can measure wavefront errors caused by micron-level roughness, but they must address interference fringe distortion caused by cylindrical curvature. While atomic force microscopy (AFM) can achieve nanoscale characterization, it is limited by its scanning range and speed. In actual production, white-light interferometers combined with multi-scale analysis algorithms are often used to balance efficiency and accuracy. Furthermore, online inspection systems integrate spectral analysis and scatterometry to provide real-time feedback on processing parameters, forming a closed-loop control loop.
The impact of cylinder lens surface roughness on beam quality spans the entire chain of light scattering, wavefront distortion, and energy loss. Its control requires the integration of precision machining, materials science, and optical inspection technologies. Future development directions include developing low-damage machining processes, constructing roughness-beam quality prediction models, and promoting the industrial application of ultra-smooth surface preparation technologies to meet the stringent beam quality requirements of cutting-edge fields such as high-energy lasers and quantum communications.
