Collection: Raman Filter

In Raman spectroscopy, optical filters play a critical role in isolating the weak Raman signal from the intense Rayleigh scattering, leading to clearer and more accurate spectral results. Here's what you need to know about filters for Raman:

Key Functions:

• Laser Line Blocking: Block the intense laser line (excitation wavelength) at the source to prevent it from overwhelming the much weaker Raman signal. This is typically achieved with:
  • Notch filters: Highly effective at blocking a narrow band around the laser line while transmitting Raman signals.
  • Edge filters: Block all wavelengths shorter than a specific cutoff, including the laser line.

• Scattered Light Rejection: Remove unwanted scattered light from the environment or sample that can interfere with the Raman signal. This might involve:
  • Longpass filters: Block wavelengths shorter than a specific cutoff, allowing only longer Raman wavelengths to pass.
  • Bandpass filters: Transmit a specific range of wavelengths around the expected Raman shift region, focusing on the signal of interest.

Wavelength Selection:

• Laser Line Blocking: Choose a filter based on your laser excitation wavelength (e.g., 532nm, 785nm, 1064nm) with a narrow bandwidth to effectively block the line while minimizing Raman signal loss.

• Scattered Light Rejection: The choice depends on the specific application and sample. Longpass filters are often used for basic rejection, while bandpass filters offer more targeted selection based on the expected Raman shift.

Additional Features:

• Steepness: Affects the sharpness of the transition between passband and stopband. Steeper transitions provide better selectivity but might reduce transmitted intensity.

• Peak Transmission: Represents the percentage of light at the desired wavelengths that passes through the filter. Higher transmission allows stronger signals but might require balancing with steepness.

• Material and Construction: Different materials (e.g., glass, dichroic coatings) influence performance, durability, and cost. Consider environmental factors like temperature and humidity.