Overview

An etched optical slit is a precision aperture formed by photochemical machining in a thin metal foil, producing the narrow, straight opening that spectrometers, monochromators and optical sensors use to admit a controlled band of light. The slit geometry is imaged onto a photoresist mask, developed, and the unprotected metal is dissolved in an alloy-matched etchant. Because the metal is removed chemically rather than cut with a blade or laser, the slit edges come out straight, burr-free and free of the recast layer and heat tint that degrade the optical profile.

The decisive requirement is slit width accuracy and edge quality. An etched optical slit holds a tightly controlled width along its entire length, and both edges are straight and square rather than tapered or ragged, so the light that passes through is cleanly defined with minimal scattering and diffraction artifacts. The process also makes the slit repeatable from part to part, which keeps spectrometer calibration stable across instruments. Thin foils of stainless steel, molybdenum and nickel provide the stiffness and low thermal expansion that optical systems need, and the same artwork can produce single slits or arrays of slits at near-zero incremental cost.

Parameter Window

• Available Materials: stainless steel 304, molybdenum, nickel, Invar
• Material Thickness Range: 0.02–0.3 mm
• Tolerance: ±0.005 mm on slit width, ±0.02 mm on slit length and position
• Minimum Feature: 0.01 mm slit width, 0.05 mm spacing between multiple slits
• Surface Options: black oxide, matte finish, electroless nickel, bare foil
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Slit Review — Convert the slit drawing to vector artwork, confirm slit width, length and position, and check edge-straightness requirements.
2. Material Selection — Choose molybdenum for low expansion, stainless 304 for stiffness, nickel or Invar where a specific CTE is required.
3. Cleaning & Lamination — Degrease the foil and laminate dry film resist so no bubbles sit along the slit edges, which would spoil straightness.
4. UV Exposure — Expose through high-resolution film with the slit pattern registered to the sheet edge for panel-level accuracy.
5. Development — Wash out unexposed resist to open the slit, then inspect the resist edge for under-development or raggedness.
6. Etching — Spray-etch in alloy-matched chemistry; slit width and edge straightness are set by time, temperature and conveyor speed.
7. Stripping & Finishing — Remove resist, neutralize, then blacken or plate; optical measurement confirms width and straightness before release.
8. Inspection & Packaging — Verify slit width, straightness, length and surface finish against the approved sample, then pack in trays or sleeves.

Core Advantages

1. Precise slit width: Photographic definition holds the slit width within ±0.005 mm along the full length.
2. Straight, burr-free edges: Chemical removal leaves no recast, taper or burr, so the optical profile stays clean with low scatter.
3. Repeatable apertures: Every slit in a batch matches the master, keeping spectrometer calibration stable across instruments.
4. Thin and low-expansion: Molybdenum, Invar and stainless foils give the stiffness and thermal stability optics demand.
5. Slit arrays at no extra cost: Multiple slits or coded apertures etch in one step, with spacing controlled photographically.
6. No-tooling iteration: A new slit geometry is a new film, so widths and patterns can change in hours — an etched optical slit stays economical through design revisions.

Typical Applications

• Spectrometer entrance slits: Precision apertures that define the light admitted to grating and prism spectrometers.
• Monochromator slits: Adjustable-width slit sets that select a narrow wavelength band for analysis.
• Spatial filter apertures: Fine slits for laser spatial filtering and beam cleanup in optical benches.
• Encoder and position slits: Narrow apertures on optical encoders and position sensors for precise edge detection.
• Photometer and radiometer slits: Apertures that limit the field of view in light measurement instruments.
• Multi-slit and coded apertures: Arrays of slits for multi-channel spectroscopy and imaging applications.

Design Notes & Process Considerations

1. Slit width callout: State the nominal slit width and its tolerance, typically ±0.005 mm, and specify whether the width is critical or nominal.
2. Edge straightness: Call out straightness per unit length and require burr-free edges, since ragged edges scatter light and widen the effective slit.
3. Material and CTE: Choose molybdenum or Invar where thermal stability matters, stainless where stiffness and cost lead.
4. Surface finish: Specify black oxide or matte finish to suppress stray reflections that would add background to the signal.
5. Length and position: Give slit length and position tolerance relative to a datum edge, since mounting alignment depends on them.
6. Slit spacing: For arrays, specify center-to-center spacing and require uniform width across all slits so each channel reads the same.