Needs and facts

• Low-frequency Raman bands (lower than 50 cm^-1) exist in certain proteins. They are dependent upon the conformation of the protein molecule, but are relatively independent of the form of the sample, i.e., whether it is a film or a crystal.

• In amorphous glasses, most of the Raman spectra present a low frequency response called "boson peak". To study the liquid-glass transition by Raman spectroscopy it is necessary to have a very efficient Raman equipment (triple monochromator T64000 type from Horiba Jobin-Yvon) and expensive.

• Much minerals present low frequency vibration modes, i.e. sulfur between 0 and 250 cm^-1, or organic materials like L-Cystine between 0 and 800 cm^-1.

• Single-wall and multi-wall carbon nanotubes exhibit radial breathing mode (RBM) vibrations in the range 150–200 cm^-1 which are used to characterize diameter distribution and overall quality of nanotubes as well as influence of external factors.

• Quality of semiconductor multi-layered structures (superlattices) is assessed by observing folded acoustic (FA) modes in the range 0–100 cm^-1.

• The Relaxation modes in liquids, binary mixtures and solutions, in the range 0–400 cm^-1, help to determine their dynamic structure.

OptiGrate^TM's new filters enable breakthrough in advanced Raman instrumentation

Orlando, Fla.... (Sept. 27, 2010) - OptiGrate Corp., an Orlando-based high tech company, has launched a complete product line of new ultra-narrow notch and bandpass filters for Raman spectroscopy applications.

"This new filter technology will make a crucial impact on the Raman instrumentation world." says OptiGrate's CEO Dr. Alexei Glebov. "The filters enable measurements of ultra-low frequency Raman bands with "standard" instruments, while earlier, it was only possible with more complex, bulky, and obviously more expensive tools. This will largely facilitate an access to ultralow frequency Raman studies, which are vital for many applications in nanotechnology, pharma, semiconductor processing, and so on."

Hans-Jürgen Reich, director of the Raman division of HORIBA commented that "This is an exciting development in Raman spectroscopy and is an ideal illustration on how the technique is moving out from the research laboratory and into the analytical world. No longer confined to large research systems or complex and expensive instruments such as Far IR or TeraHertz spectrometers, the new ULF module opens up this field to the routine analyst – measurements in a few seconds or minutes are obtained with no fuss and without limitation. It has the potential to advance Raman spectroscopy in some very important applications like pharmaceutical development and semiconductor processing."

Installed on LabRam^TM HR spectrometer manufactured by Horiba Scientific Jobin-Yvon, the following performances are achieved :

   Conclusions

The module developed is designed for specific wavelengths. Currently, 785 nm, 633 nm, 532 nm and 488 nm have been tested.

Easy access to both Stokes and Anti-Stokes Raman signal is now enabled down to very low frequencies on a single stage multichannel spectrometer with the ULF module. The transmission window of volume Bragg grating (VBG) filters extends to above 2.5 microns, so the ULF accessory opens the possibility to make simultaneous measurement of low frequency Raman as well as photoluminescence signal.

Diode lasers require perfect filtering to avoid influence from the laser sidebands so Raman spectra excited at 785 nm below 20 cm^-1 were not achieved with the laser source available at the time. Additional work is in progress to provide a solution in the short term.

Users who have applications that require access to even louver Raman frequencies, multiple excitation wavelengths, or tunability of the excitation wavelength (for resonance studies for example) are still better fitted with the use of a Triple monochromator such as the HORIBA Jobin-Yvon T64000.

Application field is very large :

• Pharmaceutical polymorphs

• LA modes of polymer

• Semiconductor lattices and nanostructures

• Material : phase/structure

• Metal Halides

• Gases

• Carbon nanotubes

• Micro, nano-crystallites