The Cairn OptoScan Monochromator has both an entrance and an exit slit, each with independently adjustable widths.

  • The exit slit width defines the bandwidth only if the input beam size is zero. The maximum exit slit width allows for a 30 nm bandwidth. 

  • In reality, the input light beam has a nonzero size, and its width is limited by the entrance slit width. 

  • The maximum entrance slit width is matched to the maximum exit slit width, ensuring any central wavelength ray within the accepted beam passes through.

    - Since the exit slit width allows a 30 nm spread, the entrance slit width is also limited to 30 nm. 


Key Considerations:

  • Fig. 1 (below) illustrates how passband shapes change as slit widths are adjusted. The Full Width at Half Maximum (FWHM) remains 30 nm, but the spectral profile varies. 

  • For light-limited fluorescence imaging, there is no practical benefit to setting different widths for the entrance and exit slits, as the improved spectral profile does not compensate for reduced intensity. 

  • If the application is not light-limited, a smaller entrance slit may be useful for tighter bandpass characteristics.


Software control:

- The OptoScan software allows users to set the center wavelength and adjust the slit widths.

- Some software versions include a "bandwidth" parameter, automatically setting both slit widths simultaneously—this option is recommended when available. 

Fig. 1:

Fig1 Illustrating Passband Shapes Changing as Adjusted

The OptoScan is optimized for narrow bandwidths, so we recommend arc lamps with high point intensity for the best performance.

We offer two 75W lamps, both with high point intensity, making them suitable for monochromators:

  • Ushio 75W lamp:

    - Ultra-stable, ultra-bright

    - Long-life (1500 hours)

    - Recommended for demanding applications 

  • Osram 75W lamp:

    - Less expensive alternative 

    - Shorter life (400 hours)

    - Still provides good monochromator performance


Recommendation:

Always keep a backup lamp in the lab in addition to the one in use.

These lamps are normally held in stock and available through our sales team.

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