  POLAR is a compact wide field space-borne detector dedicated for precise
measurements of the linear polarization of hard X-rays emitted by transient
sources in the energy range from 50 keV to 500 keV. It consists of 1600 plastic
scintillator bars grouped in 25 detector modules that are used as gamma-ray
detection material. Its energy range sensitivity is optimized for detection of
the prompt emission photons from the gamma-ray bursts. Measurements of the GRB
polarization provide unique information on emission mechanisms as well as on
composition and structure of the GRB jets. The POLAR instrument was developed
by international collaboration of Switzerland, China and Poland. It was
launched in space on-board the China Space Laboratory TG-2 on September 15th,
2016. Based on the ground calibration data, several high voltage and threshold
settings were calculated and verified in order to obtain various energy ranges
and optimized signal to background conditions for different measurement
purposes. In this paper we present optimization procedure details and current
test results.
