Magnesium Fluoride (MgF₂) Viewports for Vacuum Systems: Specifications, Applications, and Flange Selection Guide

Introduction

Magnesium Fluoride (MgF₂) viewports are high-performance optical windows designed for vacuum and ultra-high vacuum (UHV) systems where exceptional ultraviolet (UV) transmission and durability are required. Known for their ability to transmit deep into the vacuum ultraviolet (VUV) region (down to ~120 nm) and extend into the infrared, MgF₂ viewports are widely used in advanced optical and scientific applications. Their combination of broad spectral transmission, mechanical strength, and chemical resistance makes them an ideal choice for environments requiring stable and reliable optical access.

Why Choose Magnesium Fluoride Viewports?

Magnesium fluoride is a unique optical material that excels in UV-intensive applications while maintaining strong durability:

• Ultra-Broad Transmission Range: ~0.12 µm (VUV) to ~7–8 µm (IR), covering one of the widest optical ranges available

• Excellent UV Performance: One of the few materials capable of transmitting at Lyman-alpha (~121 nm)

• High Durability: Resistant to thermal shock, mechanical stress, and chemical exposure

• Low Refractive Index: Minimizes reflection losses and improves transmission efficiency

• Birefringent Properties: Can be optimized through crystal orientation for specialized optical systems

These characteristics make MgF₂ viewports especially valuable in UV optics, laser systems, and high-energy scientific environments.

Typical Specifications of Magnesium Fluoride Viewports

Firebird Optics’ MgF₂ viewports are engineered to meet the demands of precision vacuum systems and optical applications. Typical specifications include:

• Material: Single-crystal Magnesium Fluoride (MgF₂)

• Transmission Range: ~120 nm to 7 µm (VUV to IR coverage)

• Surface Quality: 60/40 scratch-dig (optical standard)

• Flatness: Up to λ/4 @ 632 nm

• Leak Rate: ≤ 1 × 10⁻¹⁰ mbar·L/s (He)

• Pressure Range: Atmosphere to high/ultra-high vacuum (~10⁻⁹ mbar typical)

• Operating Temperature: Up to ~120–200°C depending on sealing method

• Flange Materials: Stainless steel (304L, 316L/316LN)

• Parallelism: < 3 arc minutes

• Coatings: Optional AR or wavelength-specific coatings

Custom sizes, coatings, and configurations are available to meet specific system requirements.

Applications of Magnesium Fluoride Viewports

UV & Excimer Laser Systems

MgF₂ viewports are ideal for excimer lasers and UV optical systems, where deep UV transmission and high laser durability are critical.

Spectroscopy & Analytical Instruments

Their wide spectral range makes them suitable for UV, VIS, and IR spectroscopy, enabling accurate multi-wavelength analysis.

Space & Aerospace Applications

Due to their ability to transmit VUV wavelengths and withstand harsh environments, MgF₂ viewports are commonly used in space optics and satellite instrumentation.

Semiconductor & Vacuum Processing

MgF₂ viewports provide reliable optical access in vacuum chambers, plasma systems, and semiconductor manufacturing equipment, particularly in UV-based processes.

Research & High-Energy Physics

These viewports are used in UHV research systems and advanced physics experiments, where optical precision and vacuum integrity are essential.

Flange Options: CF vs KF vs ISO

Selecting the appropriate flange type is essential for ensuring compatibility and performance within your vacuum system. MgF₂ viewports are available in CF, KF, and ISO configurations, each suited to different applications.

CF (ConFlat) Flanges – For Ultra-High Vacuum (UHV)

• Seal Type: Metal-to-metal seal using copper gasket

• Vacuum Range: UHV (down to ~10⁻¹¹ mbar)

• Temperature Capability: Highest bake-out performance

Best Applications:

• Semiconductor fabrication

• Surface science

• Particle physics

• Permanent vacuum installations

Why choose CF?
CF flanges provide the most reliable, leak-tight seal, making them ideal for critical UHV environments and high-temperature applications.

KF (Quick Flange) – For Flexible Vacuum Systems

• Seal Type: Elastomer O-ring with clamp

• Vacuum Range: Rough to high vacuum

• Temperature Capability: Moderate

Best Applications:

• Laboratory setups

• R&D systems

• Systems requiring frequent assembly or maintenance

Why choose KF?
KF flanges allow for quick assembly and disassembly, making them ideal for modular or experimental setups.

ISO Flanges – For Large Vacuum Systems

• Seal Type: O-ring or bolted flange

• Vacuum Range: High vacuum

• Temperature Capability: Moderate

Best Applications:

• Large vacuum chambers

• Industrial processing systems

• Applications requiring larger viewing areas

Why choose ISO?
ISO flanges are designed for large-scale vacuum systems, offering strong mechanical support and scalability.

Custom Magnesium Fluoride Viewports

Firebird Optics offers fully customizable MgF₂ viewports tailored to specific application requirements, including:

• Custom diameters and thicknesses

• UV-optimized or broadband anti-reflective coatings

• Specialized flange materials or non-magnetic configurations

• Integration into complex vacuum assemblies

Customization ensures optimal performance for demanding optical and vacuum environments.