LIQUID SPECTROSCOPY
Spectra of some substances and light sources

 
Experimental configution.

The spectrograph is an Alpy 600 model linked to a multimode 50 microns optical fiber. The resulting resolution power is R = 300.

The relative substance absorbance (A) is given by the equation:
Wavelength are in Ansgtoms

Some light source (measured on a commun white screen - the daylight is the reference)

Note: LED lamps are the future of urban lighting !? It is equivalent to a permanent exposition to a white computer screen....
It is not a very excellent new for your eyes and astronomical electronic detectors.

The red vertical line in the plots indicate hydrogen Halpha line position. The argon lamp (Filly model) is used for spectral calibration.

Application to optical filter transmission measure
The setup is similar (50 microns fiber, Alpy 600 spectral resolution reduced to R = 300),
but the optical beam is collimated at filter level for supress spectral shift effect (caused rays tilt in an interference filter)

Optical transmission measure of two standard Halpha hydrogen filters. The central wavelength of each filter is significantly shifted with respect to the theoretical Halpha wavelength (red vertical line). This is a common problem, unfortunately! For the filter #1, the measured FWHM is 11 nm (specified to 13 nm), but the central wavelength transmission is at 654.0 nm (Halpha line wavelength is 656.3 nm).

The problem is more critical for filter #1, because in a converging beam of rays, the central wavelength is more blue-shifted.