  The large-scale deep underwater Cherenkov neutrino telescopes like
Baikal-GVD, ANTARES or KM3NeT, require calibration and testing methods of their
optical modules. These methods usually include laser-based systems which allow
to check the telescope responses to the light and for real-time monitoring of
the optical parameters of water such as absorption and scattering lengths,
which show seasonal changes in natural reservoirs of water. We will present a
testing method of a laser calibration system and a set of dedicated tools
developed for Baikal- GVD, which includes a specially designed and built,
compact, portable, and reconfigurable scanning station. This station is adapted
to perform fast quality tests of the underwater laser sets just before their
deployment in the telescope structure, even on ice, without darkroom. The
testing procedure includes the energy stability test of the laser device, 3D
scan of the light emission from the diffuser and attenuation test of the
optical elements of the laser calibration system. The test bench consists
primarily of an automatic mechanical scanner with a movable Si detector, beam
splitter with a reference Si detector and, optionally, Q-switched diode-pumped
solid-state laser used for laboratory scans of the diffusers. The presented
test bench enables a three-dimensional scan of the light emission from
diffusers, which are designed to obtain the isotropic distribution of photons
around the point of emission. The results of the measurement can be easily
shown on a 3D plot immediately after the test and may be also implemented to a
dedicated program simulating photons propagation in water, which allows to
check the quality of the diffuser in the scale of the Baikal-GVD telescope
geometry.
