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Unlike simple apertures (which only control beam size), these plates serve as structural elements in optical systems, providing a rigid platform for beam manipulation while maintaining alignment. They are available in a wide range of materials to match application needs: fused silica (for UV-NIR transparency, 190-2500 nm), N-BK7 (cost-effective visible-NIR, 400-2000 nm), and specialized metals like titanium (for reflective or high-temperature applications). Typical configurations include 3-5 mm diameter holes with ±0.1 mm tolerances—sizes chosen to accommodate common laser beam diameters (1-4 mm) while minimizing beam clipping. The hole’s position can be fully customized: centered (for coaxial beam paths), off-axis (for beam displacement), or in arrays (for multi-beam systems), making them suitable for diverse setups from laboratory interferometers to industrial laser machines .
Precision Hole Machining for Minimal Beam Distortion: Standard hole diameters of 3 mm and 5 mm are drilled using laser ablation (for glass substrates) or CNC milling (for metal substrates), resulting in ultra-clean edges (burr height <3 µm) and high circularity (<0.01 mm deviation from perfect circle). This precision ensures that the hole acts as a clean aperture, avoiding beam scattering (scattering loss <0.5%) that would degrade image quality or measurement accuracy. Custom hole sizes (0.1 mm to 20 mm) are available, with laser drilling enabling smaller holes (<1 mm) and CNC milling for larger, thicker plates (>10 mm thickness) .
Diverse Material Options Tailored to Wavelength and Environment:
Fused Silica: Ideal for UV (190-380 nm) and high-power applications, with high transmittance (>90% at 300 nm) and laser damage resistance (LIDT >10 J/cm² at 355 nm, 10 ns pulses). Its low thermal expansion (0.55 × 10⁻⁶ /°C) makes it suitable for temperature-stable systems.
N-BK7: Cost-effective for visible-NIR (400-2000 nm), with transmittance (>92% at 550 nm) and good mechanical strength (Young’s modulus 82 GPa). Ideal for general-purpose setups like beam combiners.
Titanium: Used for reflective or high-temperature applications, with high reflectance (>85% at 1064 nm) and thermal resistance (operating temperature up to 300°C). Its corrosion resistance (resistant to saltwater and acids) makes it suitable for marine or industrial environments .
Optical-Grade Surface Quality for Low Scatter: Glass plates feature a 60-40 scratch-dig surface finish (per MIL-PRF-13830B standards), meaning no scratches deeper than 60 µm or digs (pits) larger than 40 µm. This minimizes light scattering (scatter loss <1% at 550 nm), critical for imaging systems where stray light reduces contrast. Metal plates (e.g., titanium) have a matte finish (Ra <1 µm) to reduce glare in reflective applications .
Tight Dimensional Tolerances for Alignment: Thickness tolerance is ±0.1 mm (e.g., 5 mm thick plate ±0.1 mm), ensuring consistent beam path length across multiple plates in a system. Parallelism between the two flat surfaces is ≤5 arcminutes (0.083°), preventing beam tilt (tilt <0.1°) that would misalign downstream components. For high-precision systems (e.g., interferometers), parallelism can be tightened to ≤1 arcminute (0.017°) .
Custom Configurations for Specialized Needs: Beyond standard single-hole designs, plates can be manufactured with multiple holes (arrays of 2-100 holes) for multi-beam systems (e.g., laser printing). Edge treatments include chamfering (45° angles, 0.5 mm width) to prevent chipping during mounting and black anodization (for metal plates) to reduce stray light. Coatings are also available: AR coatings (for glass plates, <0.5% reflectance per surface) to increase transmission, or high-reflection (HR) coatings (for metal plates, >95% reflectance) for beam steering .
Beam Combining and Splitting: Enable coaxial transmission of multiple laser beams in spectroscopy and laser processing systems. For example, in a Raman spectroscopy setup, a fused silica plate with a 3 mm hole combines the excitation laser (532 nm, passing through the hole) and the collected Raman scattered light (reflected off the plate’s AR-coated surface), directing both to a detector. This coaxial design reduces system size by 50% compared to off-axis combiners .
Waveplate Integration in Polarization Systems: Allow return beam paths in polarization-sensitive setups (e.g., ellipsometers, polarimeters) where waveplates are used to manipulate polarization. A plate with a centered hole is mounted behind a waveplate: the incident beam passes through the hole and waveplate, reflects off a sample, and returns through the waveplate— the plate’s flat surface then reflects the beam to a detector, avoiding the need for a separate mirror .
Optical Filtering and Aperture Control: Combine aperture control with wavelength selection when using colored glass substrates (e.g., Schott BG39 for IR blocking). For example, a BG39 glass plate with a 4 mm hole acts as both an IR filter (blocks >99% of light >1100 nm) and an aperture (limits beam diameter to 4 mm), used in visible imaging systems to reduce thermal noise from IR light .
System Alignment and Reference Markers: Serve as reference targets in complex optical assemblies (e.g., telescope systems, laser trackers) to calibrate component positions. A plate with an off-axis hole (5 mm offset) is mounted as a fixed reference—lasers are aligned to pass through the hole, ensuring that all components are positioned within ±0.01 mm of their design location. This reduces alignment time by 30-40% compared to using multiple reference mirrors .
Medical Devices and Minimally Invasive Surgery: Facilitate laser delivery and imaging in endoscopic systems (e.g., laparoscopic surgery). A titanium plate with a 2 mm hole is integrated into the endoscope tip: the hole delivers the surgical laser (1064 nm) to the tissue, while the plate’s reflective surface channels imaging light (400-700 nm) back to the camera. The titanium’s biocompatibility (meets ISO 10993 standards) ensures safety for in-body use .
Material selection depends on wavelength transparency and application requirements:
UV (190-380 nm): UV-grade fused silica is the only choice, as it transmits >90% of UV light—N-BK7 absorbs >50% of UV light <300 nm. Fused silica also resists UV-induced yellowing (a common issue with other glasses).
Visible (400-700 nm): N-BK7 is cost-effective and transmits >92% of visible light, making it ideal for general-purpose use. For high-power visible lasers (e.g., 532 nm, 10 W), fused silica is preferred for its higher LIDT (>10 J/cm² vs. 5 J/cm² for N-BK7).
NIR (700-2500 nm): Fused silica (transmittance >90% up to 2500 nm) or germanium (for mid-IR, 2-14 µm, transmittance >40% at 10 µm) are used. Infrared is opaque in visible light, so it requires IR alignment tools.
Reflective Applications (Any Wavelength): Titanium (reflectance >85% 400-2000 nm) or aluminum-coated glass (reflectance >90% visible-NIR) are suitable—titanium offers better corrosion resistance for outdoor use .
Centered holes (hole axis = plate optical axis) maintain coaxial beam paths, with no lateral displacement. Off-axis holes introduce lateral displacement (Δx), calculated as: Δx = Hole Offset × sin(θ), where θ is the incident angle of the beam relative to the plate’s normal. For example, a plate with a 5 mm offset and θ=10°: Δx = 5 × sin(10°) ≈ 0.87 mm. This displacement is intentional in systems like beam shifters, where the plate moves the beam without changing its direction. To avoid unintended misalignment, off-axis holes must have offset tolerance ±0.05 mm—larger tolerances (±0.1 mm) can cause Δx variation of 0.017 mm, which may misalign small-beam systems (<1 mm diameter) .
