If your fiber laser cutting head is giving hazy cuts, dull edges, or a sudden power drop on thin sheet, the first thing worth checking is the protective window in front of the focusing lens. This is the genuine Raytools protective lens, 27.9 mm diameter x 4.1 mm thickness - the focusing-side window used in BM109, BM111, BM114S, BT210S, BT240S and BT240S-RC heads. It's currently in stock and dispatches within 1-3 business days from our Ahmedabad warehouse, with delivery across India.
Raytools heads use two different protective windows - a smaller one near the collimation lens (usually 24.9 x 1.5 mm) and this one near the focusing lens (27.9 x 4.1 mm). The two are not interchangeable, and a mismatched thickness can shift the focal point enough to affect cut quality. This window is made from high-purity fused silica with anti-reflective coating on both faces for 1064-1080 nm fiber lasers, giving over 99% transmittance. It's built to be the sacrificial part - it takes the spatter and heat so the actual focusing lens underneath doesn't have to. If you're not fully sure this is the size your head needs, check the section below before ordering.
Specifications
Specification
Detail
Diameter
27.9 mm
Thickness
4.1 mm
Material
Fused silica (quartz)
Coating
AR-coated both faces, 1064-1080 nm
Transmittance
99%+
Position in head
Focusing lens protective window
Head compatibility
BM109, BM111, BM114S, BT210S, BT240S, BT240S-RC
Recommended power range
Up to 6 kW
Stock status
In stock, ships in 1-3 business days
How to Confirm This Is Your Size
Check your head model - BM109, BM111, BM114S, BT210S, BT240S and BT240S-RC all use this window on the focusing side.
Measure the current window with a caliper - a reading close to 27.9 mm diameter and 4.1 mm thickness confirms the match.
Check the position - this window sits closer to the nozzle end, not the laser-input side (that's the smaller 24.9 x 1.5 mm collimation window).
Still unsure? Send us a photo of your cutting head on WhatsApp and we'll confirm the exact part before you pay.
Signs You Need to Replace It
Burn marks, pitting or a cloudy surface on the window
Rough edges or dross sticking on thin sheet cuts
Sudden drop in effective laser power at same settings
Spatter or dust buildup that won't clean off with alcohol
Any crack or chip near the beam path
Cut quality that was fine last week, not fine today
Features & Benefits
Features
Genuine Raytools fused-silica window, dual-side AR coating tuned for 1064 nm, exact 27.9 x 4.1 mm fitment for BM/BT series drawer-type lens holders, high laser-damage threshold for continuous production use.
Benefits
Protects the costlier focusing lens underneath, keeps cut edges clean and consistent, avoids unplanned downtime from a cracked or hazed window, and is priced as a routine consumable rather than a repair.
Genuine Raytools vs Generic Lens
Parameter
Genuine Raytools (this product)
Generic / Unbranded
Substrate
High-purity fused silica
Mixed-grade, often undocumented
AR Coating
Tuned for 1064-1080 nm
Inconsistent or missing on one face
Transmittance
99%+
Varies, often lower
Damage Threshold
Rated for production use
Burns and pits faster
Fitment
Exact drawer-slot fit
Tolerance mismatches common
Why Order This From Us
Genuine Raytools optics - not relabeled or mixed-source glass
In stock right now - dispatched in 1-3 business days
GST-registered supplier (GSTIN 24AFSFS3212F1Z2) with proper invoicing
Ahmedabad-based warehouse with pan-India courier reach
WhatsApp support to confirm fitment before you order
Bulk pricing for job-work shops and fabrication units
Frequently Asked Questions
It's the focusing-side protective window inside Raytools BM and BT series cutting heads. It shields the focusing lens from spatter, smoke and heat, and is designed to be replaced instead of the lens itself.
BM109, BM111, BM114S, BT210S, BT240S and BT240S-RC all use the 27.9 x 4.1 mm window on the focusing side.
Yes. The 24.9 x 1.5 mm window protects the collimation lens near the laser-input side. This 27.9 x 4.1 mm window protects the focusing lens near the nozzle side - they're not interchangeable.
Yes, this is a genuine Raytools fused-silica protective window, not a generic replacement.
It's in stock and dispatches within 1-3 business days, with courier delivery across India.
Yes, every order ships with a proper GST invoice for your records.
Look for pitting, burn marks, haze, or a drop in cut quality on thin sheet - any of these mean it's time to swap it out.
Yes, bulk pricing is available - message us on WhatsApp with your quantity for the best rate.
In stock, dispatched in 1-3 business days, with GST invoice and pan-India delivery. Message us on WhatsApp if you'd like fitment confirmed before ordering, or request a quote for bulk quantities.
