BH-S20 Shortpass Filter
Ultra-sharp blue edge for narrow-band transmission and precision excitation filtering.
- Passband: 406 – 425 nm, 90.1 – 91.5 % T (± 0.7 % ripple)
- Cut-off (T50): ≈ 432 nm
- Edge steepness: ~18 nm (90 → 10 % transition)
- Blocking: < 0.98 % T above 450 nm (OD ≥ 2)
- AOI: 0° (normal incidence); custom angles available
- Construction: Ion-assisted hard-oxide; 5 – 450 mm shapes, 0.21 – 3.8 mm thick
- Custom options: Edge tuning, ripple smoothing, 45° AOI, rapid prototypes
Learn more
BH-S20 Hybrid delivers Passband 406 – 425 nm, 90.1 – 91.5 % T (± 0.7 % ripple), Cut-off (T50) ≈ 432 nm, and Edge steepness ~18 nm (90 → 10 % transition).
The hard-oxide coating is built for repeated handling, heat, and cleaning.
Best suited for:
Narrow-band excitation filtering, high-precision fluorescence, laser systems, UV-visible spectroscopy.
Description
The BH-S20, designated Cold Blue (C-B435), provides a steep shortpass cut-off at 432.2 nm. The passband spans 385 to 429 nm with average transmission around 88 %, peaking at 91.5 % near 423 nm. Blocking is deep and broad: transmission drops below 1 % by 446 nm and averages just 0.3 % from 446 to 742 nm, suppressing the entire visible spectrum from blue through deep-red. A faint rise appears above 742 nm but stays below 5 % at 780 nm. This is one of the shortest-cut-off filters in the KUPO line-up, isolating only the deep violet window.
Key Advantages
- 432 nm ultra-short cut-off – Among the shortest cut-offs available, passing only deep violet and near-UV while blocking everything from blue through NIR.
- OD 2.5+ broadband blocking – Average transmission just 0.3 % from 446–742 nm delivers OD 2.5 or better across 300 nm of bandwidth.
- 91.5 % peak in violet passband – High throughput in the 385–429 nm window preserves UV-A and violet excitation energy.
- Hard-oxide durability – Ion-assisted sputtered coating survives high-power UV sources, humidity, and aggressive cleaning.
- Custom formats – Round, square, or free-form blanks from 5 mm to 450 mm, thickness 0.21–3.8 mm, on Borofloat, soda-lime, Schott D263 T, or Corning Eagle XG glass.
Typical Applications
- UV-A/violet excitation isolation – Passes 405–430 nm excitation lines for DAPI and Hoechst stains while blocking all visible emission wavelengths.
- Forensic UV imaging – Isolates the deep-violet illumination window for latent evidence detection with no visible light contamination.
- Photolithography – Confines broadband UV source output to the near-UV/violet band, preventing longer-wavelength exposure of photoresists.
- Laser clean-up for 405 nm diodes – Removes ASE and sideband emission from 405 nm laser diodes, delivering a spectrally pure beam for optical data storage or bioanalysis.
- Sterilization monitoring – Isolates UV-A energy for germicidal effectiveness measurements while blocking visible indicator light.
Need a deep-violet shortpass in a custom format? KUPO Optics delivers prototypes in days and scales to volume – contact us with your specs.
FAQ
BH-S20 FAQ
What is BH-S20 and what is it used for?
BH-S20 is a 435 nm Shortpass Filter (Cold Blue Grade). The BH-S20, designated Cold Blue (C-B435), provides a steep shortpass cut-off at 432.2 nm. The passband spans 385 to 429 nm with average transmission around 88 %, peaking at 91.5 % near 423 nm. Common uses include UV-A/violet excitation isolation, Forensic UV imaging, Photolithography, and Laser clean-up for 405 nm diodes.
What are the key optical specs of BH-S20?
Key published specs for BH-S20 include Passband: 406 – 425 nm, 90.1 – 91.5 % T (± 0.7 % ripple); Cut-off (T50): ≈ 432 nm; Edge steepness: ~18 nm (90 → 10 % transition); Blocking: < 0.98 % T above 450 nm (OD ≥ 2); AOI: 0° (normal incidence); custom angles available.
What applications is BH-S20 best suited for?
BH-S20 is commonly used for UV-A/violet excitation isolation, Forensic UV imaging, Photolithography, and Laser clean-up for 405 nm diodes. UV-A/violet excitation isolation - Passes 405-430 nm excitation lines for DAPI and Hoechst stains while blocking all visible emission wavelengths.
Can BH-S20 be customized for size, substrate, or coating requirements?
KUPO lists the construction for BH-S20 as Ion-assisted hard-oxide; 5 – 450 mm shapes, 0.21 – 3.8 mm thick. Published custom options include Edge tuning, ripple smoothing, 45° AOI, rapid prototypes. Custom formats - Round, square, or free-form blanks from 5 mm to 450 mm, thickness 0.21-3.8 mm, on Borofloat, soda-lime, Schott D263 T, or Corning Eagle XG glass.
What should I know about angle of incidence and durability for BH-S20?
The published angle of incidence for BH-S20 is 0° (normal incidence); custom angles available. The hard-oxide coating is built for repeated handling, heat, and cleaning.
