This device is designed for monitoring the beam pointing stability and the beam collimation in HALCYONE and HELIOS spectrometers. In both transient absorption and fluorescence upconversion experiments there are two beams focused in the same spot. One of these beams is sent through a variable optical delay stage, which changes the optical path length for this beam by as much as 2 meters. This makes the alignment of an optical delay stage a critical requirement for obtaining reliable data. Most commonly the wavelength of the beam sent through the delay stage is around 800 nm. This wavelength is difficult to see by eye, which poses additional difficulties for the delay stage alignment. A silicon sensor in a camera on the other hand can detect light around 800 nm very well and therefore produces a clear image of a beam profile.
There are two main parameters you can control with this alignment tool to insure adequate performance of your optical delay stage:
Beam Collimation: If the beam going through the delay stage is not well collimated, the size of the focus will change as the optical path length changes. This will affect the overlap between the two beams and result in erroneous data. With our alignment tool a user can carefully monitor the beam profile and make the necessary adjustments to the beam collimating optics (if applicable).
Beam Pointing: If the delay stage is not properly aligned, the beam pointing will change as the stage is translated from one end of the track to the other. This will in turn affect the spatial overlap of the two beams and result in inaccurate data. Beam pointing is the most frequently checked parameter. We recommend verifying the delay stage alignment every day.
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