The key to determining the quality of a dichroic mirror lies in its comprehensive performance of optical properties, manufacturing processes, and environmental adaptability. High quality dichroic mirrors should have precise spectral response, high reflection/transmission efficiency, excellent surface quality, and long-term stability, especially in precision optical systems where any small deviation may affect overall performance.
1、 Key Quality Assessment Indicators
Spectral performance: reflectivity and transmittance
High quality dichroic mirrors should achieve high reflectivity (>95%) and high transmittance (>90%) within the target wavelength range, while having extremely low transmission or reflection in non target bands.
For example, a DM505 lens used for fluorescence microscopy should have high reflectivity in the 400-450nm wavelength range and high transparency in the 500-700nm wavelength range, with a steep transition band to avoid signal crosstalk.
The measured data needs to be validated using a spectrophotometer (such as PerkinElmer Lambda1050+).
Wavelength Range and Cut off Characteristics
Clearly calibrate the working band (such as visible light 380-780nm or specific laser lines such as 532nm) and ensure stable performance within this range.
The "cut-off" of short wave or long wave lenses should be sharp, that is, the transition interval from high reflectivity to high transparency should be as narrow as possible to improve spectral accuracy.
Incident angle sensitivity (angle tolerance)
Most dichroic mirrors are designed for use at a 45 ° incident angle, where high-quality products perform best and remain stable even when changing within a range of ± 5 °.
Products with strong angle dependence may cause optical path deviation or efficiency reduction, affecting system alignment.
Surface Quality and Defect Control
The surface roughness should be ≤ 0.5nm (Ra), and the scratch/pitting grade should comply with the 20/10 standard (ISO10110-8).
Medical or research grade lenses require higher surface cleanliness to avoid scattering and signal attenuation.
Film adhesion and environmental stability
The film layer needs to be tested using the cross cut method (ASTM D3359 Class 4B) to ensure that it does not peel off.
After 500 cycles of temperature cycling (-40 ℃~+85 ℃), the performance degradation is ≤ 0.3%, reflecting its durability.
Under humid and hot conditions (such as 85% RH, 85 ℃), it can still maintain stable performance and comply with the ISO9211-4 standard.
Base material and damage threshold
Fused silica or K9 glass substrate is preferred. The former has low thermal expansion coefficient and is suitable for high-power laser applications.
High quality lenses have a damage threshold of>5J/cm ² under 1064nm laser, making them suitable for ultrafast laser systems.
