Frequency instability measurements of the CH3OH optically pumped laser at 70.5 and 118 µm

This paper reports frequency instability measurements made on two optically pumped CH3OH waveguide lasers working at 4.25 THz (70.5 μm) and at 2.52 THz (118 μm). The two-sample standard deviationσy(τ)is measured on the beat note generated by a point contact metal-insulator-metal diode. A fractional value of about2 · 10⁻¹²and4 · 10⁻¹²is reached over a 50 ms time interval, for the 70.5 μm and 118 μm line, respectively, of the free-running laser.