An ultrastable metrology laser for traceable length metrology in nanopositioning machines – Towards a 10−12 uncertainty level

In this contribution we propose the incorporation of a diode laser stabilized to an ultrastable cavity (ORS) as a metrology laser within the interferometric length measurement system of a nanopositioning and -measuring machine with a lateral measurement range of 200 mm. Based on a frequency instability analysis of the ORS against a GPS-referenced frequency comb we observed a frequency drift of 6.2 kHz(Δf/f = 1.3∙10 −11 ) during the course of one day and peak-to-peak variations below 81 kHz (Δf/f = 1.7∙10 −10 ) over observation times up to ten days. Within daily operation of the NPMM-200, the influence of cavity-related frequency changes practically falling below the current digital resolution limit of the interferometric measurement system (2.86∙10 −11 ) and can therefore be neglected, if a sufficient predetermination of the absolute frequency using an optical frequency comb has been applied. To guarantee an absolute tracking of the laser frequency within a non-stop service operation of the ORS at an uncertainty level of 1∙10 −12 , a suitable correction for the long-term frequency changes of the cavity with the help of the frequency comb has to be established.