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As a primary category of edge filters (alongside longpass filters), they enable precise separation of UV (175–400nm), visible (400–700nm), and near-infrared (700–1200nm) wavelengths, supporting applications from prototyping (e.g., academic research) to high-volume industrial use (e.g., consumer electronics manufacturing). Our shortpass filters are engineered using advanced thin-film coating technology (ion-beam sputtering, IBS) to achieve steep transition edges (<10nm between 90% and 10% transmission), high short-wavelength transmission (>94% below cut-off), and deep long-wavelength blocking (OD 4.0+). Unlike conventional shortpass filters that suffer from "blue shift" (cut-off wavelength decrease) at non-normal incidence, our filters maintain <2nm cut-off shift at 15° incidence, ensuring consistent performance in diverse optical layouts. With substrate options including UV fused silica (for UV/visible) and N-BK7 (for visible/NIR), they cater to needs from UV lithography to consumer camera systems.
Cut-off Wavelengths: Available from 400nm to 1600nm, with 50% transmission points (cut-off, T50) at standard values like 450nm (blue/green separation), 600nm (yellow/red separation), and 740nm (visible/NIR separation). Custom cut-off wavelengths (e.g., 350nm for UV detection, 1000nm for short-wave IR blocking) are available to fit specialized applications—such as 500nm cut-off filters for green laser harmonic separation .
High Transmission: Ensures >94% transmission below the cut-off wavelength, with options for 300–1030nm (visible-focused) and 200–1650nm (UV-to-NIR) ranges. This high transmission is achieved through optimized thin-film designs: 40–60 layers of HfO₂/SiO₂ for visible wavelengths, and MgF₂/Al₂O₃ for UV wavelengths. For example, a 600nm cut-off filter transmits 400–595nm light with >95% efficiency, ideal for visible imaging systems .
Effective Blocking: Attenuates longer wavelengths with OD 4.0+ (OD 4 = 99.99% blocking), ensuring minimal interference from unwanted long wavelengths. For example, a 740nm cut-off filter blocks 745–1600nm NIR light with OD 4.5, making it suitable for visible cameras where NIR light would cause color distortion. Blocking can be customized to OD 6.0+ for high-sensitivity applications (e.g., low-light imaging) .
Dual Coatings: Front-surface edge transmission coatings (optimized for shortpass performance) paired with rear-surface anti-reflection (AR) coatings minimize losses. The AR coating reduces reflection to <0.5% per surface in the passband, improving overall throughput and reducing ghosting in imaging applications. For UV applications, we use UV-transparent AR coatings (e.g., MgF₂) to avoid UV absorption .
Surface Quality: Meets 20-10 or 10-5 scratch-dig standards (per MIL-PRF-13830B) to ensure image clarity. A 10-5 surface (10 scratch width, 5 scratch density) reduces light scatter in high-resolution microscopy, ensuring sharp images of biological samples stained with UV/visible dyes. Surface flatness is <λ/4 (λ=633nm) for precision optical systems (e.g., laser interferometers) .
Standard Sizes: 25mm diameter as standard, with ±0.1mm tolerance to fit standard optical mounts (e.g., Thorlabs SM1 threads). Custom sizes (12.5–100mm diameter, 20×20mm square) accommodate specialized systems—such as 100mm diameter filters for large-format projectors or 12.5mm filters for compact microscopes. Thickness options (1–3mm) balance mechanical stability and weight .
Angle Tolerance: Optimized for normal incidence (0°), with 0±2° angle of incidence specifications to minimize cut-off wavelength shift. At 2° incidence, the cut-off wavelength shifts by <1nm—negligible for most applications. For systems requiring non-normal incidence (e.g., 10°), we offer custom filters with pre-compensated cut-off wavelengths to maintain performance .
Spectral Analysis: Isolates UV/visible wavelengths from infrared background in spectroscopy. In UV-visible spectrophotometry, a 350nm cut-off filter blocks 355–1200nm light, ensuring only UV light (200–350nm) reaches the detector—critical for analyzing UV-absorbing compounds (e.g., nucleic acids, vitamins) .
Microscopy: Blocks NIR heat in fluorescence imaging to protect samples. In live-cell fluorescence microscopy, a 650nm cut-off filter blocks 655–1200nm NIR light (which generates heat that can damage cells) while transmitting 400–650nm visible light for imaging, extending cell viability during long-term experiments .
Lighting Systems: Shapes color temperature in projectors and stage lighting. LED projectors use 620nm cut-off filters to block 625–700nm red light, adjusting the color temperature from 5000K (cool white) to 3000K (warm white) to match ambient lighting. Stage lighting systems use 500nm cut-off filters to create blue/green lighting effects without red tint .
Laser Harmonics: Separates fundamental laser wavelengths from higher harmonics. Nd:YAG lasers generate 1064nm fundamental light and 532nm second harmonic light— a 600nm cut-off filter transmits 532nm light while blocking 1064nm light, enabling use of the second harmonic for green laser applications (e.g., laser pointers, display technology) .
UV Detection: Enhances ultraviolet sensors in environmental monitoring. Ozone detectors use 300nm cut-off filters to block 305–1200nm light, ensuring only 280–300nm UV light (absorbed by ozone) reaches the sensor—enabling accurate measurement of atmospheric ozone concentration (±0.01 ppm) .
Night Vision Cameras: Blocks long-wavelength noise for improved low-light sensitivity. Military night-vision goggles use 700nm cut-off filters to block 705–900nm NIR light (emitted by enemy night-vision devices) while transmitting 400–700nm visible light, reducing glare and improving target detection in low-light conditions .
Q: How is the cut-off wavelength defined?
A: The cut-off wavelength is where transmission drops to 50% of the peak value (T50), with steep transitions (<10nm) between the transmitted (shorter wavelengths, >90% transmission) and blocked (longer wavelengths, <10% transmission) regions. For example, a 600nm cut-off filter has >90% transmission at 595nm, 50% at 600nm, and <10% at 605nm. This steep transition ensures precise spectral separation—critical for applications like laser harmonic separation or color temperature control .
Q: What is OD 4.0 blocking?
A: OD 4.0 means only 0.01% of unwanted longer wavelengths transmit—equivalent to 99.99% blocking. This deep blocking is essential for eliminating interference from long wavelengths. For example, a 740nm cut-off filter with OD 4.0 blocks 99.99% of 745–1600nm NIR light, ensuring no NIR-induced color distortion in visible imaging. For high-sensitivity applications (e.g., low-light microscopy), we offer OD 6.0+ blocking (99.9999% blocking) to further reduce background noise .
Q: Can shortpass filters be used in laser systems?
A: Yes, they’re ideal for separating laser harmonics (e.g., transmitting 532nm second harmonic while blocking 1064nm fundamental in Nd:YAG lasers). Standard shortpass filters handle moderate laser power (up to 1W/cm² CW at 532nm) for applications like laser imaging. For high-power systems (e.g., 10W CW lasers, 1J/cm² pulsed lasers), inquire about our high-damage-threshold variants—these use thicker substrates (3–5mm UV fused silica) and enhanced coatings (e.g., TiO₂/SiO₂) to achieve LIDT up to 5J/cm² @ 1064nm, 10ns pulses, preventing coating degradation .
