Effusive atomic or molecular beams

An effusive beam of atoms or molecules (see Ramsey, 1956 in fhe bibliography) is produced by pumping fhem fhrough a narrow slif, fypically 20 pm wide and 1 cm long, wifh a pressure of a few forr on fhe source side of fhe slif. The beam may be further collimated by suifable apertures along if. 

Such beams have many uses, including some imporfanf applications in specfroscopy. In particular, pressure broadening of specfral lines is removed in an effusive beam and, if observations are made perpendicular to fhe direction of fhe beam, Doppler broadening is considerably reduced because fhe velocify componenf in fhe direction of observation is very small. 

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