Abstract
Profiles of the 422·7 nm calcium line emitted by an electronically modulated hollow cathode lamp (50 % duty cycle, 20 mA square wave current) are measured as a function of modulation frequency. The optical system provides for resolution in time (60 μs) wavelength (3 × 10 −4 nm) and space (0.5 mm). Self-reversal and the line width increase with radial distance from the center of the cathode bore, increase with time during the pulse and decrease with increasing modulation frequency (up to 6400 Hz). Up to 1600 Hz, electronic modulation yields narrower and more intense lines than d.c. operation combined with optical chopping, In an appendix it is shown that the apparent line profile observed with the aid of a lock-in amplifier may change with the phase adjustment of the amplifier.
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