808nm Bandpass Filter

An 808nm bandpass filter allows only light centered around the 808nm wavelength to pass through while significantly reducing the transmission of other wavelengths.

  • Application 1: In infrared spectroscopy, it helps isolate the 808nm wavelength to accurately analyze the absorption characteristics of samples containing specific chemical bonds that interact with this wavelength.
  • Application 2: For 808nm - pumped solid - state lasers, the filter ensures that only the 808nm pump light reaches the laser medium, optimizing the laser's pumping efficiency and output performance.
  • Application 3: In bio - imaging, when using 808nm - emitting fluorescent probes, the filter enables the clear visualization of the probes by filtering out background light and only allowing the 808nm fluorescent signal to be detected.

808nm Filter Selection Guide: Configuration Analysis Based on Typical Applications

I. Filter Selection for Laser Pumping Systems

In the pumping optical path of solid-state lasers (such as Nd:YAG, Nd:YVO₄), 808nm filters must meet the following core configurations:

1. Central Wavelength & Bandwidth:

  • Strictly lock the central wavelength at 808±2nm with a half-bandwidth controlled within 5-10nm.
  • Narrow bandwidth design prevents efficiency degradation caused by pump source wavelength drift (e.g., Nd:YAG crystal absorption efficiency decreases by 30% when the 808nm pump source drifts to 810nm).

2. Transmittance & Cut-off Characteristics:

  • Achieve peak transmittance >95% in the 808nm band, with a cut-off depth >OD6 (transmittance <0.0001%) for the 1064nm laser output wavelength.
  • High transmittance ensures efficient pump light injection, while deep cut-off design prevents 1064nm laser feedback from damaging the pump source.

3. Laser Damage Threshold:

  • For high-power pumping scenarios (continuous wave power >20W), the damage threshold should be ≥0.5J/cm² (10ns pulse, 532nm).
  • Dielectric film filters using ion-assisted coating technology can withstand 5 times higher energy density than ordinary absorptive filters.

4. Material & Environmental Adaptability:

  • Prefer UV-grade fused silica or BK7 glass substrates with low thermal expansion coefficients (<5×10⁻⁷/℃).
  • Maintain wavelength stability within -20℃ to 80℃ operating temperature, with wavelength drift <±0.5nm.

Selection Rationale

  1. Precise Wavelength Matching: The pump absorption peak of solid-state laser crystals concentrates at 808nm, and narrowband design enhances pumping efficiency by over 25%.
  2. Laser Isolation Requirement: Unfiltered 1064nm laser may cause self-oscillation, leading to output power fluctuations exceeding 15%. Deep cut-off design suppresses feedback light below safe thresholds.
  3. Power Tolerance: When pump power exceeds 10W, ordinary filter coatings are prone to thermal stress delamination. High-damage-threshold design ensures over 2,000 hours of continuous operation without failure.

II. Filter Selection for Laser Hair Removal Devices

In 808nm semiconductor laser hair removal systems, filters must meet the following configuration requirements:

1. Bandpass Characteristics:

  • Adopt 808±30nm wide-bandpass design to effectively filter 400-780nm visible light and 850-1100nm near-infrared stray light.
  • 60nm bandwidth covers the typical wavelength drift range (±15nm) of semiconductor lasers.

2. Transmittance & Uniformity:

  • Achieve transmittance >90% in the 808nm band with in-plane uniformity error <±3%.
  • Uniformity ensures laser fluence variation <5%, preventing local overheating that may cause ≥Grade II skin burns.

3. Anti-contamination & Durability:

  • Coat with hard TiO₂/SiO₂ multilayer films passing 5B-level cross-cut test, resistant to 500+ alcohol wipes without coating delamination.
  • Ion-sputtering coating technology increases film adhesion by 3 times, adapting to high-frequency disinfection in clinical environments.

4. Dimension & Mounting:

  • Standard size: 12-25mm diameter circular filter with frosted edges to reduce stray light reflection (<0.1%).
  • Stress-free ring mounting to avoid mechanical stress-induced wavelength shift (<±0.3nm).

Selection Rationale

  1. Optical Interference Suppression: Blocking visible light eliminates interference with CCD imaging, improving hair follicle positioning accuracy to ±0.2mm.
  2. Energy Uniformity Requirement: Fluence variation >10% reduces hair removal efficiency by 20%. High-uniformity design ensures over 95% hair follicle destruction rate.
  3. Clinical Environment Adaptation: Medical-grade hard-coat filters last 3 times longer than ordinary soft-coat filters, reducing equipment maintenance costs by 40%.

III. Selection Decision Tree & Key Parameter List

Core Parameters for Laser Pumping Systems

  • Central Wavelength: 808±2nm, wavelength drift <±0.5nm (-20℃ to 80℃)
  • Cut-off Depth (1064nm): OD6-OD8, reflectance >99.9999%
  • Damage Threshold (10ns pulse): 0.5-5J/cm², requiring >1.5x pump source peak energy density

Core Parameters for Laser Hair Removal Devices

  • Bandpass Range: 808±30nm, bandwidth variation <±5nm (mass production)
  • Uniformity Error: <±3%, in-plane transmittance standard deviation <1%
  • Anti-contamination Rating: 5B-level (cross-cut test), 500+ alcohol wipes without coating failure

Decision Recommendations

For Laser Pumping Scenarios

  • Prioritize dielectric film filters to meet deep cut-off and high-damage-threshold requirements in high-power applications.
  • For multi-wavelength systems (e.g., with 980nm monitoring light), customize dual-bandpass designs with isolation >OD5.

For Laser Hair Removal Scenarios

  • Use ion-assisted coated wide-bandpass filters to balance transmittance and uniformity.
  • Adjust central wavelength to 810-820nm for Fitzpatrick skin types Ⅳ-Ⅵ, enhancing melanin absorption efficiency by 15%.

By following these configurations, filters can systematically solve issues of wavelength matching, energy control, and environmental adaptability in laser systems, ensuring reliable performance and stability.

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