Design of Spectrometer
P&P Optica’s systems are built to provide very well defined, spectrally separated photons. Additionally, the VPH Gratings produce no ghost effects, which mean that all photons of a particular wavelength are diffracted to only a single area of the detector. Ghost effects produced by other types of gratings often create confusion in spectral information, as a portion of photons of a particular wavelength is often diffracted to a detector area corresponding to a different wavelength. The transmission design also eliminates other scatter effects often seen in scanning or reflective systems. This prevents non-diffracted photons from reaching the detector to produce noise. Finally, P&P Optica designs transmission optics to produce as few aberrations as possible. This means that multiple wavelength photons are diffracted in the same way whether at the center or edge of the detector. This eliminates washing-out of sharp peaks and peak overlap on the entire detector.
P&P Optica has developed non-scanning, low noise, high throughput transmission spectrometers covering a spectral range from 250nm to 2500nm. Low aberration optics provide the spectrometer with a large field of view with the ability to image entrance slits up to 25mm long without degradation of spectral resolution.
P&P Optica instruments are capable of measuring both broadband and Raman spectra, and enable researchers to use multichannel or high throughput modes to detect signals previously undetectable by non-scanning, optical systems. This capability is crucial for the measurement of continuously changing systems such as the human body or sensitive samples which change under observation.
The P&P Optica spectrometer has no moving parts and acquires its entire signal simultaneously for all colours. This is of particular importance in quickly changing systems such as the human body, where changes can affect signals obtained during temporal scanning.
P&P Optica’s spectrometers use a two dimensional detector to gather spectroscopic data. The most significant benefit this produces is that more data can be collected about a sample simultaneously. This advantage can be exploited in two primary ways. The first is that multiple samples can be measured using the same system in simultaneous real time experiments. This technique is useful in hyperspectral imaging, where multiple spectra from different points on an image are required to build a hyperspectral cube, allowing researchers to visualize data in three dimensions. A three dimensional image is built from multiple spectral layers of two-dimensional data, a feat which is not possible with only a one dimensional detector.
The second is that the entire detector can be dedicated to one sample, allowing exceptionally low noise performance. This is achieved by averaging, or binning, across many rows of data. The amount of rows varies with the detector in use, but can range from the neighbourhood of 128 rows up to well over 1000 rows. The benefit of having hundreds of data samples compared to having only one, as a traditional, one-dimensional spectrometer does, should be readily apparent. This directly results in a lower signal to noise ratio – for example, with 128 rows binned, a full order of magnitude improvement of signal to noise ratio is attained. In measurements where low light conditions or minute chemical concentrations make reliable data collection impossible with one-dimensional detectors, P&P Optica’s next generation 2D arrays become the only available option.
P&P Optica's patented high performance spectrometers are designed to deliver significant performance enhancements over competing optical spectrometers available in the market today. The core differentiator between P&P Optica's spectrometers and others is in the use of high-efficiency, transmission-based Volume Phase Holographic (VPH) gratings. Unlike other diffraction gratings, broadband VPH gratings provide average absolute diffraction efficiency greater than 75%. Equivalent ruled and holographic gratings have an average efficiency of around 35% in a similar configuration. Furthermore, the transmission design reduces both optical aberrations and scatter, which are known to seriously impede the results obtained with reflection based optical spectrometers.
P&P Optica produces unique, high quality VPH Gratings that provide significantly better optical qualities than traditional gratings which allow for the construction of a single stage spectrometer, outperforming double or triple stage instruments with traditional diffraction gratings. On average a broadband relief grating diffracts only 40% of photons and the remaining 60% become “noise” in the system, whereas the P&P Optica gratings diffract over 75% of photons and only 25% become “noise”.
- Provides very high throughput; essentially the spectrometer is able to count individual photons collected from the sample.
- Achieve low scattered light level, so that a very small percentage of collected photons create noise in the system.
- Provide exceptional aberration correction allowing for application of large area detectors, thereby increasing collection ability.
- Allows simultaneous registration of complete spectrum, free of ghosts and spurious peaks, so that information gathered corresponds to the state of the sample at the particular time. Many high-end spectrometers acquire spectral information by scanning wavelengths over time which distorts spectral information of dynamic samples.
- Provides high signal to noise ratio (SNR) of over 100,000:1 permitting the detection of even very weak signals which are barely above background radiation and noise levels.