Overview

A custom 304 stainless steel optical slit is a thin aperture plate that defines the beam width in spectrometers, encoders and alignment instruments, produced by photochemical machining rather than by stamping or laser cutting. A photoresist mask is exposed with the slit artwork, developed, and the unprotected 304 stainless foil is dissolved in a controlled ferric chloride spray, so slit width, edge straightness and length are set by the artwork and etch time instead of tool pressure. Typical stock is 304/316L stainless between 0.02 mm and 0.30 mm, chosen for its flatness, corrosion resistance and ability to hold a knife-edge without a burr.

For optical buyers, a custom 304 stainless steel optical slit solves three recurring problems: slit edges must be razor-straight and free of rolled burrs that scatter stray light, widths down to 0.02 mm are hard to hold with mechanical slitting, and any heat tint or recast layer degrades the blackened, low-reflectance surface the instrument needs. Chemical machining forms every aperture on a sheet at the same rate, leaving the foil flat and stress-free, with both faces etched symmetrically so the knife-edge stays sharp through coating and assembly.

Parameter Window

• Available Materials: 304 and 316L stainless steel; also copper, nickel and brass for mixed optical builds
• Material Thickness Range: 0.02–0.30 mm
• Tolerance: ±0.005 mm on slit width, ±0.02 mm on slit length and position
• Minimum Feature: 0.02 mm slit width, 0.03 mm edge-to-edge web
• Surface Options: black oxide / matte blackening, electropolishing, passivation, anti-glare coating, ultrasonic cleaning
• Compliance: ISO 9001 process control, RoHS/REACH material traceability

Manufacturing Process / Workflow (8 Steps)

1. Artwork & Nesting — Convert the slit pattern to vector art, verify width-to-thickness and web rules, and lay out panels with shared fiducials.
2. Material Certification & Prep — Confirm 304 grade, mill certificate and thickness, inspect flatness and surface, then shear to exposure size.
3. Cleaning & Lamination — Degrease and laminate dry-film resist on both faces under matched heat and pressure without trapped bubbles.
4. Dual-Side UV Exposure — Expose the slit artwork from top and bottom in precise register so both faces etch symmetrically toward a sharp edge.
5. Development — Wash out the unexposed resist to open the slit area and inspect for residue that would blunt the knife-edge.
6. Controlled Etching — Spray ferric chloride with tuned time, temperature and conveyor speed to hold width and avoid edge rounding.
7. Stripping & Blackening — Strip resist, neutralize, then apply matte blackening or electropolish for a low-reflectance, burr-free finish.
8. Inspection & Packaging — Measure slit width and straightness on a vision system, verify flatness, and pack between liners in clean trays.

Core Advantages

1. Burr-free knife edges: Chemical removal leaves no rolled burr or recast layer, so stray-light scatter at the aperture stays low.
2. No hard tooling: Each slit width is a new film, keeping one-off prototypes and frequent design revisions economical without a die.
3. Micron-level width: Slits down to 0.02 mm hold ±0.005 mm across a panel, with straight, parallel edges over the full length.
4. Stress-free flatness: With no shear or heat input, thin foil stays flat, so coating and bonding will not warp the aperture.
5. Matte low-reflectance finish: Blackening and passivation give a stable dark surface that suppresses ghost reflections in the optical path.
6. Repeatable custom geometry: A custom 304 stainless steel optical slit can combine multiple widths, lengths and arrays on one plate, reproduced from first article to volume.

Typical Applications

• Spectrometer entrance slits: Define bandpass and resolution in monochromators and spectrographs with clean, straight apertures.
• Optical encoders: Code and index slits in rotary and linear encoders where edge quality sets signal contrast.
• Alignment targets: Reticle and collimator apertures for alignment telescopes and machine-vision calibration fixtures.
• Laser beam shaping: Aperture masks that trim beam width in metrology and low-power laser projection heads.
• Medical analytical instruments: Slit plates in clinical analyzers and flow cytometers that need corrosion-resistant, cleanable surfaces.
• Aerospace sensor baffles: Light-baffle apertures in star trackers and horizon sensors where flatness and low reflectance matter.

Design Notes & Process Considerations

1. Width-to-thickness ratio: Keep slit width at or above roughly the foil thickness; very narrow slits in thick stock distort from undercut.
2. Dual-side etch callout: Specify etching from both faces so the edge stays symmetric and sharp instead of a tapered, rounded lip.
3. Edge straightness spec: State width, length, parallelism and allowable edge waviness, not just nominal width, for reliable optical performance.
4. Blackening and reflectance: Define matte finish, optical density and post-coat width tolerance, since coatings slightly change the effective aperture.
5. Web and tie bars: Leave adequate tie bars and process borders, and specify final singulation so thin webs survive stripping and cleaning.
6. Handling and cleanliness: With a custom 304 stainless steel optical slit, specify liner packaging, fingerprint control and residual-ion limits for clean optical assembly.