Examination of external cavity diode lasers’ stability by demonstrating optical beat notes through optical heterodyne experiments

The main goal of our optical heterodyne experiments is to examine the stability of our own in house-built external cavity diode lasers (ECDL) under different locking methods. In any laser system, it is of a great use to be able to identify and remove noise sources and narrow the linewidth.
Our in-house-built ECDLs' wavelength is mainly determined but has small variations due to different factors directly affecting it.
In optical heterodyne measurements, two ECDL send beams of around 780nm wavelength each and the beams are mixed to produce a beat-note with a frequency in the radio frequency(rf) range by which measurements of the frequency noise-spectrum can be taken.
Experimentally, the two single frequency output beams from the two ECDL are aligned so that they interact with each other at a non-polarizing beam splitter cube(NPBS) and then emerge into a photodetector. The amplified beat signal goes directly into the rf spectrum analyzer,which is used for the measurement of the rf beat of the two lasers. The spectrum is analyzed by measuring the line width of the spectra, which is directly related to the noise of the laser itself.
The noise of the lasers is examined for several locking schemes including side lock, peak lock, mechanical lock and current control.