Step Window

Product Overview

This design integrates two key functions: the optical performance of a standard window (transmitting light with minimal loss) and the mechanical convenience of a mounting feature— eliminating the need for separate retaining rings or clamps that would block the clear aperture. UQG Optics' step windows, a leading example, are available in a wide range of sizes to suit diverse applications: diameters from 10 mm to 200 mm (circular) and square/rectangle dimensions from 20×20 mm to 200×200 mm (polygonal), with thickness ranging from 1.50 mm (thin, compact systems) to 20 mm (heavy-duty industrial use). The stepped profile is machined with ultra-precise dimensions (step height 0.5-5 mm, tolerance ±0.10 mm) to accommodate O-rings (for sealing) or mounting flanges (for fastening), making them ideal for enclosed optical systems where environmental protection (dust, moisture) and mechanical stability are critical .

Product Features

Diverse Material Options for Wavelength and Environment: Manufactured from four primary materials, each selected for specific performance characteristics:

BK7 Glass: Cost-effective for visible-NIR applications (400-2000 nm), with transmittance >92% at 550 nm and good mechanical strength (Young’s modulus 82 GPa). Ideal for general-purpose systems like instrument enclosures.

Fused Quartz (UV-Grade): Optimized for UV-NIR transparency (190-2500 nm), with transmittance >90% at 300 nm and high laser damage resistance (LIDT >10 J/cm² at 355 nm, 10 ns pulses). Suitable for UV lasers and high-power systems.

Borosilicate Glass (e.g., Pyrex): Offers excellent thermal shock resistance (can withstand 150°C temperature changes without breaking) and transmittance >90% at 550 nm. Used in high-temperature applications like industrial ovens with optical monitoring.

Sapphire: The most durable option, with Mohs hardness 9 (second only to diamond) and transmittance >80% from 200 nm to 5 μm. Resists scratches, chemical corrosion, and high temperatures (up to 1000°C), making it ideal for aerospace and harsh industrial environments .

Precision Step Machining for Secure Mounting: The circumferential step is machined using CNC lathes (for circular windows) or CNC mills (for square/rectangular windows), resulting in consistent step height (±0.10 mm) and width (±0.20 mm). The step’s surface is perpendicular to the window’s optical axis (<0.1° deviation), ensuring that the window sits flush in the mounting housing— preventing tilting (tilt <0.05°) that would misalign the optical path. Optional angled bevels (45° or 60°, 0.5-1 mm width) are added to the step edge to facilitate easy insertion into the housing and prevent chipping .

Optical-Grade Surface Quality for Minimal Wavefront Distortion: The optical surfaces (the flat, central area of the window) meet strict quality standards:

Surface Flatness: Up to λ/4 @ 633 nm (HeNe wavelength) for high-precision systems (e.g., interferometers), meaning the surface deviates from perfect flatness by less than 158 nm (λ/4 of 633 nm). For general-purpose systems, flatness of λ/2 @ 633 nm is standard.

Scratch-Dig Finish: 20-10 (MIL-PRF-13830B) for high-end applications, with no scratches deeper than 20 μm or digs larger than 10 μm. This minimizes light scattering (scatter loss <0.5% at 550 nm), critical for imaging systems where stray light reduces contrast.

Parallelism: ≤3 arcminutes (0.05°) between the two optical surfaces, ensuring that the transmitted beam does not tilt (tilt <0.1°) as it passes through the window .

Coating Compatibility for Enhanced Performance: Step windows are compatible with a wide range of optical coatings to improve transmission or add functionality:

Broadband AR Coatings: Applied to the optical surfaces to reduce reflectance from ~4% (uncoated glass) to <0.5% per surface in a specified wavelength range (e.g., 400-700 nm