Impact of non-stationary events on low frequency homodyne detection

We present an experimental investigation into non-stationary events that occur in a homodyne detection system. The importance of non-stationary events is that it is a possible mechanism preventing shot-noise-limited homodyne detection at low frequencies, a necessary condition that needs to be routinely fulfilled in order to detect squeezed states at these frequencies. These non-stationary events are thought to arise due to airborne dust passing through the laser beam paths. We show that these non-stationary events which occur in our laboratory environment can be minimised by placing the experiment in an airtight enclosure. Isolation against non-stationary events achieved improvement of the colour of the noise spectrum by 3dB at 10Hz towards a flat shot noise spectrum and improvement in the noise distribution of the signal towards a Gaussian distribution.