I am using an Ocean Insight USB 2000+ spectrometer with a 74 DA collimator and an LS-1 Light-source with a 74-VIS collimator. I am not using any fibers. When I align my light-source and spec I loose wavelengths between 500nm and 650 nm but if they are position slightly skewed from one another I get the full spectrum my light-source is meant to output. Is this an indication my beam is not sufficiently homogenous? Would adding a fiber to my setup increase the homogeneity of my beam?
The focal length of the lens is not the same from UV to near infrared. It is therefore possible to collect more light with a slight offset for the shorter wavelengths. To make quantitative measurements of spectral intensity, it is very important to take into account this effect of the focal distance. Note that these components are designed for being used with fiber coupling which decrease the effect. For the relative calibration of a spectrometer, the protocole given by the manufacturer (that should be coming with the calibration curve) needs to be closely followed and the effect should then already be taken into account.
Those spectrometers designed to work with fibers. The same for this light source. The spectra shape depends on which reflection of one or another light source is entering to the spectrometer. The fiber would "mix" all entering light and its entrance aperture would be fixed relative to the inhomogeneities of the light beam, thus the measurements would be reproducible. The fixed position of the fiber output aperture is also important for the spectrometer wavelength calibration.
On my experience the producers of compact spectrometers: Ocean Optics, Avantes and StellarNet - provide often misleading information, however the protocole given by the manufacturer, for the relative calibration of the spectrometer, might help to understand the possible additional artifacts.
It sounds like a coupling issue and you are not optimized. The fiber as Andrei Pipa mentioned is designed to be used with the system and it could be that with the fiber you will have optimal coupling efficiency.
Call Ocean Optics support team; they will have the best answer.
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