405nm Bandpass Filters

405 nm bandpass filters are designed to transmit a selected violet wavelength band centered near 405 nm while reducing unwanted out-of-band light.

Applications:
- 405 nm violet laser diode source cleanup
- 405 nm LED illumination and inspection
- DAPI/Hoechst/Brilliant Violet/Pacific Blue-type fluorescence excitation
- 405 nm resin, photopolymer, adhesive, and violet exposure systems
- Detector-side violet signal isolation before cameras, photodiodes, PMTs, or spectrometers

Bandwidth options:
- 1 nm, 8 nm, and 10 nm FWHM for narrow 405 nm laser-line selection
- 20 nm and 30 nm FWHM for balanced LED cleanup, excitation control, and usable violet signal
- 40 nm, 50 nm, and 55 nm FWHM for higher violet output in illumination or exposure systems

Select the bandwidth based on the light source, target material or sample, detector sensitivity, blocking range, and required signal level.

405 nm violet laser diode

Use CWL 405 nm with 1–10 nm FWHM for 405 nm violet laser diode line selection, source cleanup, or detector-side isolation of a 405 nm laser signal.

405 nm violet laser diodes, including InGaN-based diode sources, are narrow-line sources compared with LEDs and lamps. For laser-line filtering, the key specs are CWL near 405 nm, FWHM such as 1 nm, 8 nm, or 10 nm, high transmission at 405 nm, and OD blocking across the unwanted wavelength range.

405 nm LED or LED array

Use CWL 405 nm with 10–30 nm FWHM for most 405 nm LED systems that need a practical balance between violet output cleanup and usable signal.

405 nm LEDs have broader emission than laser diodes, so 10 nm, 20 nm, or 30 nm FWHM options are often practical for illumination, fluorescence excitation, inspection, and exposure systems. Use 40–55 nm FWHM when the setup needs more violet-region output and can accept broader wavelength selection.

Broadband UV-visible source

Use CWL 405 nm with 20–50 nm FWHM to select a practical violet band from xenon, mercury-xenon, halogen, or other broadband UV-visible sources.

For broadband illumination, the filter extracts a 405 nm-centered band from a wider spectrum. Use 20–30 nm FWHM when the setup needs a more defined violet band. Use 40–55 nm FWHM when higher transmitted signal is more important for illumination, imaging, or detection.

DAPI / Hoechst / Brilliant Violet / Pacific Blue-type fluorescence excitation

Use CWL 405 nm with 20–50 nm FWHM for violet excitation channels such as DAPI/Hoechst-type nuclear stains or Brilliant Violet/Pacific Blue-type fluorescence channels.

For fluorescence microscopes, flow cytometers, or fluorescence detection systems, the 405 nm filter is usually placed on the excitation side before the sample. Match the excitation filter with the light source, dichroic mirror, and emission filter set. The emission-side filter should be centered at the actual emission band, not automatically at 405 nm.

405 nm resin, photopolymer, and violet exposure systems

Use CWL 405 nm with 20–50 nm FWHM or wider for 405 nm resin exposure, photopolymer systems, UV/violet adhesives, coatings, or exposure setups.

For exposure applications, the filter defines the violet irradiation band delivered to the material. Select the FWHM based on the source spectrum, required irradiance, material sensitivity near 405 nm, and out-of-band blocking requirement.

Detector-side 405 nm signal isolation

etector-side 405 nm signal isolation
Use CWL 405 nm with 1–20 nm FWHM before a silicon photodiode, CMOS/CCD camera, PMT, or UV-visible spectrometer when the target signal is near 405 nm.

For detector-side filtering, the filter should pass the 405 nm signal while reducing unwanted background outside the target band. Use 1–10 nm FWHM when stronger wavelength isolation is needed. Use 20 nm FWHM or wider when signal throughput is more important.

US Patent 9,746,412 - Flow cytometer

Context: This patent describes a flow cytometry system that uses multiple lasers, including a violet (405 nm) laser, to analyze particles or cells flowing through a viewing zone.

Usage of Filter: The bandpass filter (specifically a 405/10 nm or 405/20 nm bandpass) is used in the detection path for the Violet Side Scatter (V-SSC) channel.

Function: It isolates the specific 405 nm light that is scattered by the cell at a 90-degree angle, while blocking any fluorescence emission (which occurs at longer wavelengths like 450 nm or 525 nm).

Result: This achieves precise measurement of the cell's internal complexity (granularity) without interference from the fluorescence signals, which is critical for distinguishing between different types of white blood cells.

US Patent 10,935,485 - Fluorescence imaging flow cytometry with enhanced image resolution

Context: This system uses a laser (often 405 nm) to illuminate a sample and generate fluorescence images to determine the chemical or physical properties of cells.

Usage of Filter: A 405 nm bandpass filter is used in the excitation path (often referred to as a "laser clean-up filter").

Function: It is placed after the 405 nm laser source but before the sample. Its function is to transmit the 405 nm laser line while blocking any "spectral noise" or Amplified Spontaneous Emission (ASE) generated by the laser diode at longer wavelengths (e.g., 420–450 nm).

Result: This achieves a "pure" excitation beam. Without this filter, the stray noise from the laser would leak into the fluorescence detection channel (which often detects DAPI signals around 460 nm), causing a high background signal and ruining the image contrast.

US Patent 20240170925 - Method for active stabilization of an injection locked laser with an optical bandpass filter

Context: This patent describes a method to stabilize a high-power single-frequency laser system using "injection locking," where a master laser controls a slave laser.

Usage of Filter: A narrow optical bandpass filter (centered at the laser wavelength, e.g., 405 nm if using violet diodes) is used in the feedback/monitoring loop.

Function: The filter is placed before a photodetector to probe the spectral mode of the slave laser. It discriminates between the desired locked mode and unwanted modes.

Result: This achieves a simple, compact, and robust stabilization of the laser frequency without needing bulky diffraction gratings, enabling high-precision applications like laser cooling or spectroscopy.

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