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 CH
3
OH waveguide lasers working at 4.25 THz (70.5 μm) and at 2.52 THz (118 μm). The two-sample standard deviation
\sigma_{y}(\tau)
is measured on the beat note generated by a point contact metal-insulator-metal diode. A fractional value of about
2 \cdot 10^{-12}
and
4 \cdot 10^{-12}
is reached over a 50 ms time interval, for the 70.5 μm and 118 μm line, respectively, of the free-running laser.