Collection: 845nm Bandpass Filter

845nm Filter Selection Guide: Application-Specific Configuration and Rationale

1. Machine Vision and Industrial Inspection Scenarios

Application Context

In industrial automation and security monitoring, the 845nm wavelength is commonly used for near-infrared (NIR) light signal transmission or target recognition. For example, some machine vision systems employ dual-light sources at 850nm and 940nm simultaneously, where the 940nm light may interfere with the 845nm signal. In such cases, the filter must precisely isolate the 845nm band to eliminate interference from other wavelengths.

Filter Configuration Requirements

1.1 Central Wavelength and Bandwidth

• The central wavelength must be strictly locked at 845nm ±5nm to match the light source characteristics.
• The full-width at half-maximum (FWHM) bandwidth is recommended to be 60nm, balancing signal strength and anti-interference capability. Excessively wide bandwidth may introduce stray light, while overly narrow bandwidth reduces light flux.

1.2 Transmittance and Blocking Depth

• Peak transmittance should be ≥90% to ensure sufficient signal intensity passes through.
• The blocking depth must achieve OD≥6 in the visible spectrum (300–827nm) and near 940nm to effectively suppress ambient light and 940nm light source interference.

1.3 Material and Coating Technology

• Adopt interference coating technology (e.g., ion beam evaporation) to ensure wavelength positioning accuracy and temperature stability.
• Select optical glass substrates (e.g., BK7) to balance mechanical strength and optical uniformity.

Selection Logic and Problem Solving

• Why Narrow Bandwidth and High Blocking?

845nm light sources often coexist with other NIR wavelengths (e.g., 940nm). A narrow-band design prevents crosstalk between adjacent bands. For instance, in night-time monitoring, 940nm light may be misidentified as a valid signal, but a filter with high blocking depth can attenuate it to less than 0.0001%, significantly improving the signal-to-noise ratio.

• Importance of High Transmittance

In industrial inspection, the reflectivity of target objects to 845nm light may be low. High transmittance compensates for signal loss, ensuring the sensitivity of the detection system.

2. Biomedical Fluorescence Imaging Scenarios

Application Context

In small-animal in vivo imaging or radionuclide labeling studies, the 845nm wavelength is used for fluorescence signal detection. For example, medical radionuclide-labeled fluorescent materials (e.g., EuMOF) emit fluorescence in the 500–845nm range, requiring filters to extract signals within this band.

Filter Configuration Requirements

2.1 Spectral Range and Bandwidth

• The passband should cover 500–845nm with a central wavelength of 845nm, and a recommended bandwidth of 40–60nm to adapt to the broad-spectrum characteristics of fluorescence signals.
• For higher resolution (e.g., distinguishing adjacent fluorescence peaks), narrow-band filters with bandwidth ≤20nm can be selected, though light flux must be balanced.

2.2 Transmittance and Blocking Characteristics

• Transmittance ≥90% ensures effective capture of weak fluorescence signals.
• The blocking depth must reach OD≥4 in the visible spectrum (e.g., 400–700nm) and long-wave infrared (900–1100nm) to suppress autofluorescence from biological tissues and ambient infrared interference.

2.3 Angular Dependence and Surface Quality

• Wavelength drift caused by angular deviation must be controlled (e.g., wavelength shift <5nm at incident angles ≤10°) to avoid imaging distortion.
• Surface quality should meet MIL-spec 40/20 to minimize scattering and stray light.

Selection Logic and Problem Solving

• Balancing Broadband and NarrowbandFluorescence signals typically have wide emission spectra (e.g., 500–845nm). Excessively narrow bandwidth may lose part of the signal, but in multi-color fluorescence imaging, narrow-band filters are necessary to separate signals from different markers (e.g., distinguishing 845nm and 750nm fluorescence to avoid overlap).
• Necessity of Blocking DepthBiological tissues exhibit autofluorescence in the visible range (400–700nm), while long-wave infrared (e.g., 940nm) may originate from equipment light sources or environmental radiation. High blocking depth reduces these interferences below the detection threshold, enhancing imaging contrast.

3. Photothermal Effect Research Scenarios (Extended Application)

Application Context

In laser photothermal effect experiments, 845nm lasers are used to induce localized temperature increases in cells or materials. For example, patch-clamp techniques combined with 845nm lasers can study the effects of temperature changes on ion channel kinetics.

Filter Configuration Requirements

3.1 Wavelength Purity and Bandwidth

• The central wavelength must precisely match the laser source (845nm ±2nm) with a bandwidth ≤20nm to concentrate laser energy on the target wavelength.
• If the laser has wavelength drift (e.g., ±5nm), filters with bandwidth ≥10nm should be selected to accommodate source fluctuations.

3.2 High Transmittance and Low Absorption

• Transmittance ≥95% minimizes energy loss in the filter, avoiding inaccuracies in photothermal effect measurements.
• Substrates should use low-absorption glass (e.g., fused silica) to prevent filter overheating under high-power laser irradiation.

3.3 Laser Damage Resistance

• Filters must pass laser damage threshold tests (e.g., 1064nm, 10ns pulse, damage threshold >5J/cm²) to ensure stability under high-power lasers.

Selection Logic and Problem Solving

• Synergy of Narrowband and High Transmittance

Photothermal effects rely on efficient laser energy transfer. Narrow-band filters eliminate energy interference from other wavelengths, while high transmittance maximizes laser energy delivery to the sample. For example, a 10% energy absorption by the filter in cell experiments could cause temperature measurement errors exceeding 10%.

• Importance of Damage Resistance Design

High-power lasers (e.g., continuous wave >1W) may damage filter coatings or crack substrates. Selecting laser-resistant coating processes (e.g., ion beam sputtering) and materials (e.g., sapphire) is critical for reliability.

4. Selection Decision Tree

4.1 Define Core Requirements

• For multi-light source interference rejection (e.g., machine vision): Prioritize narrow-band (60nm) filters with high blocking (OD≥6).
• For weak fluorescence signal detection (e.g., biomedical imaging): Balance bandwidth (40–60nm) and transmittance (≥90%).
• For laser experiments: Ensure wavelength accuracy (±2nm) and laser damage resistance.

4.2 Parameter Priority Ranking

• Machine vision: Blocking depth > Bandwidth > Transmittance
• Biomedical imaging: Transmittance > Bandwidth > Blocking depth
• Laser experiments: Wavelength accuracy > Damage resistance > Transmittance

4.3 Verify Compatibility

• Match with light source spectrum: Confirm the overlap between the light source's central wavelength and the filter's passband.
• Match with detector response: Silicon detectors have high response at 845nm, while InGaAs detectors cover a broader range.

By following this configuration logic, users can accurately select 845nm filters for specific applications, addressing core issues such as signal interference, insufficient sensitivity, or laser energy loss.