  We present a subHz linewidth portable ultrastable laser with the mass and
volume of are 40kg and 400mm*280mm*450mm, respectively, that meets the
requirements of automatic frequency locking and road transportation. A dynamic
analytical model of the physical parts of ultrastable laser is established, and
the first order resonance frequency is determined by FEA and well agrees with
the experimentally measured result. To verify the transport performance of the
portable ultrastable laser, it is tested for 100 km actual road transportation
and 60 min continuous vibration, corresponding to 1700 km road transportation.
The success of the test demonstrated that the portable ultrastable laser was
very robust. Meanwhile, the portable ultrastable lasers shows that the median
of the linewidth distribution is approximately 0.78 Hz, and the fractional
frequency instability is less than 3E-15 at 1 to 10 s averaging time. This
value approaches the total noise of 2.0E-15 including thermal noise and
residual amplitude modulation. The robust suggested that the portable
ultrastable laser might be a good candidate such as optical frequency transfer
and metrological systems.
