What Optical Designers Need To Know about High LIDT Optical Components' Manufacturing
With the continual development of optical technology, the demand for optical components capable of processing high-power laser beams has increased by double digits in recent years. This increase is primarily a response to the steady increase in power of continuous wave (CW) and pulsed solid-state fiber lasers and disk lasers.
As the power of CW and pulsed lasers increases, pulse widths also range from milliseconds to nanoseconds, which successively promotes the expansion of laser cutting, drilling, welding, marking, and 3D printing applications. At an equivalent time, higher power ultrafast lasers have quickly entered the assembly stage from the laboratory. These laser sources with picosecond and femtosecond pulse widths became the idea for brand spanking new laser processing applications within the production of semiconductors, electronics, and medical equipment. High-power fiber lasers also are widely utilized in the military field.
Another important trend is that the ever-expanding wavelength range, especially within the deep ultraviolet and visual (for example, blue and green) parts of the spectrum, where high-power lasers can now be used. These also provide new applications for material processing.
Demanding top quality for each component
The laser field requires top quality for each component, and optical component suppliers must have good internal control capabilities. Industrial users and suppliers cannot accept that differences between components and production batches cause unexpected degradation or failure of laser equipment or laser processes.
A common thanks to specifying the standard of high-power laser optics is to define the laser-induced damage threshold (LIDT). LIDT is that the maximum laser radiation that will be processed by optical elements with zero probability of injury.
Specifying and testing high damage threshold laser (HDTL) optics are often challenging. Many variables affect the damage threshold. Failures are statistical and depend upon laser, environment, and other variables that don't have anything to try to do with optical components. additionally, the perceived reliability of the component may depend upon how the test data is interpreted. Therefore, pre-defining the wants of the optical lenses and an idea to realize these requirements consistently is important.
How manufacturers make sure the consistent quality of high LIDT optics
As mentioned above, the idea of reliable HDTL optics may be a clear understanding of the applications and relationships between many quality and process parameters. Once the optical component manufacturer understands the wants, it can easily complete all production
The substrate material is that the key to the damage threshold. the fabric also affects the value of the component. The mechanical properties and chemical composition of glass are different, and therefore the processing and polishing rates are different, therefore the time interval is additionally different. Generally in theory higher purity glass is typically costlier .
Mature optical manufacturers will learn tons of data about products from major suppliers of optical materials, including the benefits and limitations of the supplier's manufacturing process.
Optical manufacturers have also introduced expertise in manufacturing partnerships to advise customers’optical design teams on the sort and manufacturer of glass, which can end in the foremost consistent performance and therefore the best trade-off between cost and quality.
Optical surface manufacturing
Manufacturing precision optical devices involves complex processes, requiring control of mechanical and fluid dynamics, chemical reactions, and structural effects on the glass surface and subsurface. Imperfections (scratches, dents, voids, cracks, and smoothness) and residual stress on the optical surface can affect the robustness of the finished part. These defects also can affect any coatings applied to the surface.
Grinding and lapping
Fabrication of laser optics begins with multiple steps of every of two processes:
1) fixed abrasive grinding, and
2) loose abrasive grinding, also referred to as lapping.
Each step gets the optic closer to its finished shape and size.
In addition, each of the steps in grinding and lapping removes open and closed subsurface microcracks mentioned as subsurface damage (SSD), produced within the previous step. A “rule of thumb” in optical fabrication is that the SSD is approximately 0.3X the mean diameter of the abrasive grit or particle. Therefore, each successive step in grinding and lapping uses a smaller grit size to scale back the SSD.
Many of the considerations for removing material and controlling surface finish in grinding and lapping also apply to mechanical and chemical polishing processes.
The primary goals of polishing high-LIDT optics are to eliminate subsurface cracks and to supply a surface having a finish better than 10 Å root mean squared (RMS). To accomplish this, IRD (Litchfield, MN) uses the results of internal and external research. This research documents the relationships between process parameters utilized in fabricating high-damage-threshold laser optics and therefore the quality of the polished surfaces.
Cleaning throughout fabrication removes lubricants, wear debris, and abrasive agents from rough and fine grinding, lapping, and polishing. Residual debris can interfere with coatings. It also can react with the glass to make local changes in optical and mechanical properties.