Thermal-Noise-Limited Transportable Ultra-stable laser

SummaryWe present the design and performance of rack-mounted transportable ultra-stable laser at 1542.44nm, which is built for non-laboratory environment. The fractional frequency instability reaches the thermal noise limit of the 5 cm cubic cavity of 2.1×10
^-15
at 1 s averaging time after 70 mHz/s linear drift removed, and the beatnote with commercial ultra-stable laser reveals a linewidth of 1.4 Hz.