Challenges and considerations in Raman

Although Raman spectroscopy has many advantages, sometimes it still needs to overcome some practical challenges. These issues occur on all Raman instruments. The solutions we provide can help you fully utilize the ideal performance of Raman systems.

Here are some practical solutions and suggestions.
1. The Raman effect is relatively weak

Renishaw's Raman system adopts efficient optical design and ultra sensitive detectors.
2. Strong fluorescence background will mask Raman spectral bands

When using a multi laser system, you can switch to a different excitation wavelength. For example, switching from visible light to near-infrared laser (such as 785 nm) can typically reduce fluorescence intensity, thereby helping to generate spectra with clear Raman bands.

3. Many samples have uneven surfaces

In the past, Raman imaging of non-uniform samples was very difficult. Now, with the help of LiveTrack real-time focusing tracking technology, Renishaw micro Raman spectrometer can automatically maintain focus while collecting data. You can easily study how chemical composition and structure change with surface morphology.

4. Glass containers and microscope cover slides can mask the Raman spectral bands of the sample

a. Replace the glass microscope cover slip with a stainless steel cover slip.

b. For biological cells, mirror polished stainless steel, CaF2 or MgF2 microscope coverslips can be used.

c. Replace the standard glass container with quartz, which produces a lower back bottom than the standard glass at a wavelength of 785 nm.

5. Containers and substrates can also affect spectra

You can control the degree of confocal microscopy Raman spectrometer and Raman analyzer. Combining high numerical aperture (N.A.) microscope objectives with highly confocal instrument settings can significantly reduce sampling volume. This helps eliminate any unwanted backing data from the substrate or container material.

When analyzing block samples in transparent containers, you can use a low numerical aperture lens to focus on the container. This is another method to enhance the Raman signal of the target substance and minimize the interference of the container on the spectrum.

6. High laser power can damage the sample

We use laser to generate Raman scattering. The Raman signal is directly proportional to the laser power, so the higher the power, the stronger the signal is usually.

However, all samples have a laser power density threshold, and once exceeded, it may cause structural or chemical changes in the sample. Our solution is as follows:

a. Design of high-throughput spectrometer; You can generate strong Raman signals with very low laser power.

b. The laser power is controlled by software and can be repeated. This way, you can be sure that your sample will not change.

c. Use line focusing mode to disperse the incident laser power over a larger sample area. This solution can be achieved using a micro Raman spectrometer, RA802 drug analyzer, and RA816 biological analyzer.

7. Software automatically removes cosmic rays

Cosmic rays are high-energy particles that come from outside the Earth's atmosphere. If cosmic rays affect the detector during data acquisition, high-intensity peaks will appear in the spectrum. Large area Raman images typically contain thousands of cosmic ray artifacts.

 Software can fully automatically remove cosmic rays from large-area Raman images containing up to 50 million spectra. Then we can automatically run the data analysis workflow to generate reliable results.

Spatial resolution of Raman images

The following factors determine the spatial resolution of a micro Raman spectrometer:

• Laser spot size
This is a function of the numerical aperture (NA) of the objective lens and the wavelength of the laser. In short, a higher numerical aperture and shorter wavelength will result in a smaller spot size.

The spacing between spectral collection points on the sample (sampling)

This is the function of the sample stage. Renishaw's MS30 high-speed grating ruler feedback platform has a large stroke range and small step sizes as low as 50 nm. These step sizes are smaller than the minimum laser spot size limited by diffraction.

Magnification factor of optical components and CCD pixel size in spectrometer

It is ultimately limited by the inherent waveform nature of light, reaching a level slightly smaller than micrometers.