Spectroscopy, in its broadest sense, is the term given to the investigation and measurement of spectra produced when a substance interacts with or emits electromagnetic radiation. All known matter absorbs or emits light and, depending on the frequency at which the interaction with light occurs, will emit a unique spectrum.
Image Credit: IS-Instruments, Ltd.
It is, therefore, an extremely useful tool both for studying molecules and for determining the composition of an unknown substance. Depending on the substance being measured, different wavelengths are used, and this can vary depending on the substance’s state (solid, liquid, gas) as well as the type of substance it is (biological, organic, inorganic, etc.).
Wavelength is, therefore, crucial in spectroscopy, and to achieve the best results, the right wavelength must be selected. Used in various industries and sectors, spectroscopy is also widely used in space science for studying spectral emission lines.
In fact, two of the founding directors have extensive experience in space science, having worked on projects with both the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA), respectively.
The team at IS-Instruments (ISI), back on Earth, specializes in the design and production of compact remote sensing equipment. This is particularly the case in Raman spectroscopy, where equipment is designed for use in nuclear decommissioning, biopharmaceuticals, pharmaceuticals, high-value manufacturing, and other sectors.
IS Instruments have a core range, which comprises a portfolio of High Etendue Spectrometers (HES) available with a choice of excitation wavelengths. In addition to these, IS Instruments has also developed ODIN, the name given to their latest compact deep UV Raman spectrometer, which offers fluorescence-free results.
Finally, IS Instruments is currently developing its gas phase Raman, which employs a hollow-core microstructured optical fiber as the sensing medium.
One question often posed to the team is, “How do you know which instrument and which wavelength to choose to deliver the best results?”
Choosing the best wavelength for optimal measurement outcomes is influenced by the specific sample being examined, as different wavelengths impact factors such as fluorescence, integration time, and resolution. Fluorescence is an absorption effect that can sometimes conceal finer details when measuring Raman scatter.
Typically, lower-powered excitation lasers require a longer integration time to produce higher-resolution spectra. To achieve spectra in a shorter time, longer wavelengths are used but can require a higher-powered laser, it must be noted that this can raise safety concerns, depending on the environment, and also increase the risk of sample damage.
The selection of shorter wavelengths can also damage samples and, in the process, change the results of the measurement.
1064 nm
Fewer molecules are absorbed in the near-infrared (NIR); therefore, a 1064 nm excitation wavelength offers superb fluorescence suppression.
When analyzing samples with a known high fluorescence background, Near-Infrared (NIR) is often utilized, yet it is important to note that NIR has the lowest scattering intensity compared to other wavelengths like 355, 532, and 785 nm.
Although 1064 nm excitation lasers are widely used to analyze highly fluorescing samples, it must be stated that they carry an increased risk of sample damage compared to the use of visible lasers. Often, this longer wavelength is used for measuring substances such as dyes, pigments, and edible oils.
785 nm
The most commonly used excitation wavelength is 785 nm. This wavelength offers a decent balance between fluorescence, spectral resolution, detector efficiency, and cost.
This wavelength produces a stronger Raman signal for over 90% of active Raman materials and carries a very low risk of damaging samples. Therefore, 785 nm is a good choice for measuring chemicals and organic materials.
532 nm
This shorter and higher-energy wavelength requires significantly less interaction time than at higher wavelengths and is, therefore, notably more efficient. Offering high sensitivity, 532 nm is the ideal choice for use in both metal oxides and inorganic materials which demonstrate low or no fluorescence.
This wavelength is most commonly used for gas phase measurements, including those for hydrogen, methane, carbon dioxide, and solvent vapors.
355 nm
Ideal for use in measuring complex biomolecules, 355 nm is also well-suited for chromophores and aromatics, which typically demonstrate high fluorescence and, therefore, cannot be effectively measured at longer wavelengths.
Invariably, these systems use high-powered gas-pumped or pseudo-pulsed lasers. They are also expensive to buy and maintain, owing to the requirement for gas purging or water-cooling. These instruments, therefore, tend to be available only at research facilities.
The deep UV Raman spectrometer from IS Instruments, ODIN, is a compact, ancillary-free instrument. ODIN is capable of unprecedented Raman characterization of complex biological material. It operates at 228.5 nm with a diode laser custom-made by Toptica and does not require a chiller unit.
ODIN, designed to fit on a desk, is notably more cost-effective compared to the instruments presently employed in academic settings. Its distinct configuration ensures maximum throughput while also reducing power density at the target, thereby minimizing the chance of sample degradation.
There are many applications to which ODIN is suited, including biomedical, security and defense, process manufacturing, and the identification of hazardous materials. ODIN has successfully measured Immunoglobulin G (IgG) in tests and identified arthritis in equine synovial fluid.
Source: IS-Instruments, Ltd.
| Wavelength (nm) |
Pros |
Cons |
| 355 |
Good for measuring biological samples in low concentration |
Sample damage. Cost. |
| 532 |
High scattering intensity, good for inorganic materials. |
High fluorescence can mask the minute spectral details. |
| 785 |
Produces a stronger Raman signal for over 90% of active Raman materials with manageable fluorescence. |
Problematic for highly fluorescing substances. |
| 1064 |
Low fluorescence. |
Low scattering intensity, potential for sample damage from powerful laser. Cost. |
IS Instruments’ gas phase instrument was developed by partners from both the Optoelectronic Research Centre at the University of Southampton, and Jacobs. The developers of the gas phase Raman instrument have been awarded a patent due to its revolutionary design.
The instrument operates at 532 nm and uses a hollow-core microstructured optical fiber to increase the path length. This increase opens up more opportunities for the gas(es) to interact with the laser to produce spectra.
Unlike gas chromatography, ISI's gas Raman can detect and determine gases without anticipatory column and detector selection. Furthermore, Aura is able to measure multiple gas species simultaneously and even identify homonuclear diatomic variations. It has additionally been used to monitor hydrogen blending within natural gas pipelines.
Today, ISI is pleased to offer a new service for one-off or ad hoc measurements. Customers can send their samples, and the team at ISI will select the optimum instrument and wavelength to achieve the best result. This removes the requirement for a customer to have in-house knowledge of instrument operation, while also reducing costs.
This information has been sourced, reviewed and adapted from materials provided by IS-Instruments, Ltd.
For more information on this source, please visit IS-Instruments, Ltd.