Laser wavelength of Raman spectrometer

Raman spectrometer is a powerful analytical tool widely used in chemistry, materials science, biomedicine and other fields. Choosing the right laser wavelength is one of the key factors to ensure the success of the experiment.

1. Excitation efficiency and signal intensity

The excitation efficiency directly affects the intensity of the Raman signal. The Raman scattering efficiency is inversely proportional to the fourth power of the wavelength. Therefore, lasers of different wavelengths exhibit different signal intensities when exciting samples:

• 532nm: Due to its shorter wavelength, the Raman signal intensity is larger, and it can produce up to 4.7 times that of 785nm and 16 times that of 1064nm. This makes the 532nm light source have obvious advantages in the analysis of samples with high signal intensity requirements, especially suitable for samples with weak Raman activity.
• 785nm: The excitation efficiency is moderate. Although the signal intensity is not as good as 532nm, it can still meet the detection needs of most samples and is suitable for routine analysis.
• 1064nm: The excitation efficiency is the lowest, and the signal intensity generated is only 6% of 532nm. It usually takes a long acquisition time to obtain sufficient signal levels, which is suitable for samples sensitive to fluorescence interference.

2. Fluorescence interference degree Fluorescence effect is an important interference factor in Raman spectroscopy analysis. Lasers of different wavelengths have different effects on fluorescence:

• 532nm: It has high energy and is easy to cause fluorescence effect in the sample, which may interfere with the Raman signal, so it is not suitable for samples with strong fluorescence.
• 785nm: It has achieved a good balance between excitation efficiency and fluorescence suppression, can effectively reduce fluorescence intensity, and is suitable for more than 90% of Raman active materials.
• 1064nm: Due to its low photon energy, the possibility of fluorescence generation is small, which is particularly suitable for the analysis of colored and dark materials.

3. Spectral range and resolution

Spectral range and resolution are important indicators for evaluating the performance of Raman spectrometers:

• 532nm: It can cover the spectral range of 65cm⁻¹ to 4000cm⁻¹, which is suitable for detecting functional groups in the high Raman shift region.
• 785nm: It provides good spectral resolution, can show more spectral details, and is suitable for structural analysis of most substances. 1064nm: Although the spectral resolution is slightly lower, it can still provide sufficient structural information while reducing fluorescence interference.

4. Applicable sample type

When choosing a laser wavelength, the sample type is an important consideration:

• 532nm: Commonly used in the study of carbon nanotubes, metal oxides, minerals and inorganic materials, suitable for Raman resonance experiments.
• 785nm: The most popular excitation wavelength at present, suitable for the analysis of most chemicals, organic materials and biological samples.
• 1064nm: Suitable for the detection of colored and dark materials and highly fluorescent samples, widely used in drug detection, food safety and other fields.

5. Instrument cost and maintenance

The cost and maintenance of the instrument are also factors that need to be considered when choosing a laser wavelength:

• 532nm: The cost of the laser and optical components is moderate, but due to its high energy, it may affect the sample and has high maintenance requirements.
• 785nm: The overall cost is low, the technology is mature, the market products are rich, and the maintenance cost is relatively low. It is a cost-effective choice.
• 1064nm: Although it has important value in high-end applications, the instrument is relatively expensive due to the high cost of components such as near-infrared detectors, and maintenance requires professional knowledge.