pilot laser ？

LIMO expands the product portfolio of compact and fully- equipped diode lasers at 1470 nm
       
At the beginning of this year, LIMO introduced the, in comparison to other products in the market,   particularly compact diode laser at a wavelength of 1470 nm. Due to the positive feedback about this new product, the wavelength 1470 nm will be included into the standard product portfolio. The output power of these fibre-coupled standard devices is measured at 12 W and 25 W, respectively. In addition, customized types with output power > 100 W are available as well.

This product line is suited for medical solutions concerning modern surgery. A high absorption in water at this special wavelength enables a user-friendly operation in surgical applications. The size of the potential-free housing has been minimized: The result is nevertheless a fully-equipped product in a compact size. Protection window, fiber-contact switch, monitor diode and pilot laser are already integrated.

Another possible, important application is pumping of Er:YAG lasers.

请教一下，pilot laser是什么东东？