High Throughput OEM Spectrometer for Raman Spectroscopy

Dr. Michael Foster, Director at IS-Instruments Ltd, talks to AZoM about high throughput OEM spectrometer for Raman spectroscopy.

Why is the new high throughput/etendue spectrometer ideal for Raman spectroscopy?

There are two main advantages. The first is that Raman signals are typically very weak and thus any method of improving the capture is desirable. Having a higher throughput/etendue spectrometer allows more Raman photons to be collected and hence can improve the sensitivity of the instrument.

Raman spectroscopy is an ideal technique for many quality control and assurance applications. This is particularly true in the pharmaceutical industry, where it can provide fast, precise identification of the chemical composition of a given material.  However, most Raman systems can only sample small areas (<< 1 mm diameter) of a given target, such as a pharmaceutical tablet, due to their limited etendue.

In order to acquire a truly accurate reading the whole sample must be measured, which requires the spectrometer to make measurements of a diffuse source that could be at least 1 – 5 mm in diameter.  The increased etendue offered by IS-Instruments HES spectrometer allows measurements to be made of these diffuse samples in a cost effective package.

How does this low cost device compare to conventional systems currently on the market?

The conventional systems in the marketplace consist of either cheap, small, portable spectrometers or expensive, large, lab-based systems.

Our aim was to produce a system that would be targeted for on-line measurements with most of the capability of the lab-based systems but at a price point comparable with the portable systems. Thus we have a performance advantage over the portable systems and a significant price advantage over the lab-based systems, making this an ideal choice for Quality Assurance type applications.

When coupled with our ability to measure larger areas of target samples the HES spectrometer has several clear advantages over the conventional systems currently on the market.

This makes the system particular suited to Transmission and stand-off raman applications.

How does this system work?

Our system can be thought of as a variant of a Fourier Transform spectrometer, but instead of forming the fringes in the time domain, they are formed in the spatial domain. This allows them to be formed in a system that requires no moving parts and hence improve reliability and lower costs while maintaining an excellent level of performance.

This device can be integrated with large receiving optics. Can you elaborate on the type of optics involved in order to be used as an OEM device?

The system was designed to be fibre coupled for ease of use and enable the OEM functionality. The large etendue allows the instrument to be coupled to large core optical fibres, up to 1.5 mm core diameters have been demonstrated. Using such large core fibres allows the system to be easily integrated into a variety of configurations of receiving optics, from simple lens arrangements to large aperture fast telescopes.

It also makes the spectrometer easy to align with external optical systems. We are also happy to adapt the system for integration with free-space optics if this is of interest to potential customers.

What would you describe as the main end-user requirements for this device?

As with any spectrometer our customers are predominately interested in the spectra resolution, the spectral range, and the sensitivity of the devices we can offer. Due to the large etendue offered by our device, there is also often a requirement for the maximum size of a target that can be sampled.  

Our systems are available with a choice of detectors matched to the specific end-user requirements. The standard model has a resolution of ~ 4.7 cm^-1 but this can be adjusted if required for more detailed measurements. Our engineers are experienced in tailoring the final solution to the customers’ ultimate requirements.

Is there a recent case study to demonstrate the application of this system in the field and how does this help tell you more about the performance of this equipment?

Yes a good example is presented on our website. This short technical note describes tests conducted using the spectrometer to make Raman measurements from a distance of 2.4 m of samples in a pressurised gas pipeline. The system was able to identify tiny samples of Xylene in less than 10 minutes. The tests show the sensitivity of the system and its suitability for applications in the field.

This is an excellent demonstration how the technology can be tailored to a specific applications in a cost effective manner.

What are the common problems that can occur with Spectrometers and how have you worked to design your OEM spectrometer to ensure these errors do not occur?

There are several issues that affect spectrometers, although no one problem could be considered common to all.  Mechanical effects, such as flexure or thermal stresses, can affect all spectrometers. Over time this may result in a spectrometer drifting, causing issues with correct identification of spectral lines or sensitivity and requiring at least recalibration.

Obviously any system is prone to these effects, but our spectrometer has been designed to offer a good compromise between the high performance of systems that require frequent maintenance and the stability of lower performance, portable spectrometers.

Our system provides very high performance but has no moving parts. This results in an inherently more stable configuration, like the portable spectrometers, but with performance closer to the lab-based set-ups.

In the unlikely event that a problem does occur, a simple recalibration procedure is provided that can be performed using standard lab contents.

Another problem we have always found with spectrometers is that the user interface is often unwieldy and non-intuitive. We have tried to design our user interface with the user in mind and make the operation as intuitive as possible. This is shown below and is simple to navigate with various options to process the data, identify the spectral peaks and adjust the display as easily as possible.

Figure 1. IS-Instruments user interface display.

Do problems such as flexure, wavelength calibration problems, and telluric matching affect the signal-to-noise ratio with your spectrometer?

As mentioned above the instrument has no moving parts and is inherently stable and thus does not have to be calibrated before every measurement. However, in the unlikely event that a problem does occur, a simple recalibration procedure is provided that can be performed using standard lab contents.

What will be the major development efforts to help evolve this device and expand its field of application?

We at IS-Instruments are continuing to work on new advances in the spectrometer design specifically trying to improve its internal transmission. As new detector technology becomes available, new models of the instrument will be produced (including possible photon counting systems using EMCCDs). We are also developing new and innovative methods of capturing the Raman photons with application use in mind. We will be putting a range of new spectrometer products and accessories on the market in the next 6 – 12 months.    

Where can we find further information?

Further information can be found at our website, or by contacting myself at [email protected].

About Michael Foster

Dr Michael Foster completed his PhD in 1999 in the study of cometary atmospheres. Due to his interest in instrumentation he then moved in to the field of LIDAR and remote sensing. He has worked in this area for the last eleven years, playing a key role in a number of space LIDAR projects including designing filtering solutions for EarthCARE, ADM (Aeolus) and the Ascope missions.

Dr Foster is recognised as one of the leading experts in the UK in LIDAR instrumentation and has worked with a number of research groups over the last ten years, developing a variety of concepts. These include UCL, Imperial College London, the University of Leicester, Open University and University of Southampton.

In 2010 with Dr Jonathan Storey Michael set up IS-Instruments to develop new solutions to industrial problems using optical instrumentation. In particular this included the development of a new high throughput spectrometer that can be used in the industrial environment.