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ABCD Matrix

UV Fused Silica

UV Fused Silica (also known as synthetic fused silica or UV-grade fused quartz) is a high-purity, amorphous silicon dioxide (SiO₂) material manufactured synthetically, typically via flame hydrolysis of silicon tetrachloride or plasma chemical vapor deposition. It is engineered for exceptional optical transmission, especially in the ultraviolet (UV) spectrum, making it a cornerstone material in lasers, photonics, and precision optics.


Key Technical Properties:


  • Transmission Range: Excellent transparency from deep UV (~160–180 nm) to near-IR (~2.5–3.5 µm), with >90% internal transmittance at 193 nm (ArF excimer laser wavelength) for thicknesses of several mm. Transmission drops sharply below ~160 nm due to the electronic bandgap of SiO₂ (~9 eV).


  • Refractive Index: Low and highly stable; at 589 nm (sodium D-line), n ≈ 1.4584. Dispersion is characterized by a high Abbe number (V_d ≈ 67.8), indicating low chromatic dispersion. The Sellmeier equation for refractive index is commonly used for design:

n2(λ)−1={B1λ2/λ2−C1}+{B2λ2/λ2−C2}+{B3λ2/λ2−C3}


​(Coefficients for Suprasil-type UV fused silica are available from manufacturers like Heraeus or Corning.)


  • Thermal Properties:Extremely low coefficient of thermal expansion (CTE): α ≈ 0.55 × 10⁻⁶ /K (near room temperature), minimizing thermal lensing and distortion under high-power laser irradiation.
    High thermal conductivity (~1.38 W/(m·K)) relative to other glasses.
    Softening point >1600 °C, excellent resistance to thermal shock.


  • Mechanical & Chemical: High hardness (Mohs ~7), excellent chemical inertness (resistant to most acids except HF), and low bubble/inclusion content (often Grade A or better per ISO 10110).


  • Laser Damage Threshold: Very high, often >10–40 J/cm² for nanosecond pulses at 355 nm (depending on surface quality and coating), due to minimal absorptive defects and high purity (<1 ppm impurities).


  • Other: Very low fluorescence and solarization (UV-induced color center formation) in premium grades; low birefringence (stress-induced <1 nm/cm).


Relevance to Lasers and Photonics:


In laser systems, UV Fused Silica is prized for its ability to handle high peak and average powers without significant absorption, nonlinear effects, or wavefront distortion. It is used in components where conventional glasses (e.g., BK7) would suffer from UV absorption or solarization.


Common Applications:


  • Excimer and UV Lasers: Windows, lenses, prisms, and beam splitters for ArF (193 nm), KrF (248 nm), and frequency-tripled/quadrupled Nd:YAG (355/266 nm) lasers. Used in stepper lithography systems for semiconductor manufacturing.


  • High-Power Laser Optics: Mirrors substrates, focusing lenses, and protective windows in industrial laser machining, ablation, and micromachining. Its low CTE reduces thermal lensing (dn/dT ≈ 10–12 × 10⁻⁶ /K).


  • Fiber Optics and Waveguides: Cladding or core material in specialty UV-transmitting fibers; substrates for fiber coupling optics and ball lenses.


  • Beam Delivery and Diagnostics: Collimating lenses, beam expanders, and attenuators. In optical amplifier chains, it serves as a low-loss substrate for mirrors and isolators. For ultrafast lasers, it is used in chirped-pulse amplification (CPA) compressor gratings or stretcher optics.


  • Astronomy and Scientific Instrumentation: Windows and lenses for laser guide stars, adaptive optics, and UV spectroscopy. Low autofluorescence benefits Raman and fluorescence microscopy.


  • Metrology and Sensing: Substrates for diffraction gratings, interferometers, and polarizers (e.g., in polarization control setups). Its stability supports high-precision ABCD matrix-based optical system design.


  • Other Photonics: Micro-optics (e.g., half-ball lenses for fiber collimation), vacuum viewports, and substrates for thin-film coatings in high-damage-threshold applications.


Practical Considerations:

  • Surface quality is critical (typically λ/10 or better flatness, <0.25 nm RMS roughness for high-power use).

  • Anti-reflective (AR) coatings are often applied to reduce Fresnel losses: R = [(n-1)/(n+1)]² per surface.

  • Compared to crystalline quartz, fused silica is isotropic (no birefringence from crystal structure) and more homogeneous.


UV Fused Silica enables reliable operation in demanding UV and high-energy laser environments where other materials would degrade or absorb excessively, directly supporting advancements in semiconductor lithography, materials processing, biomedical optics, and fundamental research.


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