Spectroscopy Academy - Raman

Examine the roots of Raman Spectroscopy. Starting with energy levels, we walk through excitation, scattering and interferences.

Raman Basics

6:00 minutes

Go behind the scenes and discover the inner workings of Raman. Three standard Raman events are explained; Rayleigh Scatter, Stokes, and Anti-Stokes.

• Virtual state (1:20)
• Rayleigh scatter (1:45)
• Stokes photon (2:10)
• Molecule energy equation (3:10)
• Anti-Stokes photon (3:30)

Fluorescence

6:45 minutes

Understand fluorescence and learn how to avoid it’s interference with the Raman spectrum.

• Ground electronic state (1:00)
• Vibrational energy states (1:45)
• Absorption of electronic energy (2:25)
• Fluorescence emitted photon (3:00)
• Critical facts of fluorescence (3:50)
• Obtain a Raman spectrum in the presence of fluorescence (5:45)

Stokes and Anti-Stokes

8:35 minutes

Learn the reasons the Stokes side of the spectrum is most commonly used. You may think it is wise to use the anti-Stoke side of the spectrum to avoid fluorescence, but you never get something for nothing and the price you pay is intensity.

• Drawing out Stokes and Anti-Stokes (1:00)
• Plotting the spectrum (2:00)
• Rayleigh scatter (3:00)
• The Boltzmann Distribution (4:25)
• Anti-Stoke intensity (5:20)
• Why Stoke spectroscopy is most common (7:00)

A discussion of why we offer multiple lasers and how FT-Raman helps avoid fluorescence.

Multiple Lasers

8:00 minutes

Learn how to achieve a virtual state to avoid fluorescence and obtain an accurate Raman scatter. Find the balance in a laser to avoid fluorescence while still gaining efficiency.

• High energy lasers (1:15)
• Fluorescence photon (2:00)
• Obtaining a virtual state and avoiding fluorescence (2:20)
• Lasers offered (3:30)
• Laser efficiency trade-off (5:00)
• Interchangeable lasers differentiation (6:40)

FT-Raman

6:00 minutes

Learn how to avoid fluorescence and obtain an efficient Raman scatter.

• Raman module that fits in sample compartment (1:40)
• 2 traditional detectors used in Raman systems (3:30)
• Avoiding fluorescence (4:00)

Examine the fundamentals of Raman – including dipoles versus polarizabilities.

Polarizability Ellipsoids

7:00 minutes

Understand the theoretical basis of what causes a molecule to scatter light. Dive into an explanation using Benzene. Learn more about polarizability - the ability to cause a change within the electron cloud.

• Explanation using Benzene (0:45)
• Fundamental rule of IR (1:00)
• Polarizability (2:25)
• What is Alpha (4:00)
• What allows the molecule to express a Raman scatter signal? (4:50)
• Induced dipoles caused by polarizability change (5:30)

Learn how using a polarized laser and analyzer can tell you even more about the molecule.

Polarization

7:00 minutes

Learn about the ability of the Raman spectrometer to be sensitive to the polarization of the light and the polarization of the scatter. 

• What is polarization (0:30)
• Classic molecule example (1:00)
• Normal modes (1:30)
• T_D symmetry (2:30)
• I_VV & I_VH (3:00)
• Polarization sensitivity (3:55)
• Polarization for the alignment of molecules (5:40)
• Overview of polarization (6:20)

Referenced recorded webinar below.

Combining what we’ve learned so far, we can now build a Raman spectrometer!

Instrumentation

11:00 minutes

Let’s get down to the instrument and how we do Raman spectroscopy.

• The laser and it’s advantages (1:00)
• The sample (2:40)
• The polarizer (3:20)
• The Raman scatter - Rayleigh and Raman light (4:00)
• The lens (4:20)
• The analyzer – 2nd polarizing element (4:50)
• The filter to eliminate the Rayleigh light (5:20)
• The diffraction element to spread the light (5:45)
• The PMT & CCD detectors (6:40)
• Spectral resolution (7:50)
• Raman popularity (9:30)

Raman Detectors

8:10 minutes

Learn what type of detectors are used in the Raman spectrometer and how they are alike, how they differ, and how do you decide which detector to use.

• Historical detectors: Photographic plate & Photo Multiplier Tube (0:30)
• CCD: Charge Coupled Device (2:50)
• EMCCD: Electron Multiplier Charge Coupled Device (4:30)
• 600 or more spectra per second with the Thermo Scientific DXR3xi Imaging Microscope (6:00)
• Which detector is right for you (6:50)

Sampling Modes

5:15 minutes

See how we present the sample to the Raman Spectrometer.

• 90° sampling (0:25)
• 180° sampling (1:30)
• Raman advantage: little sample preparation (2:55)
• Thermo Scientific DXR3 SmartRaman (4:15)