A hardware and a computative technique for tunable laser spectroscopy was developed for simultaneous measurement of Gaussian and Lorentian components of line broadening by fitting Voigt line profile. The technique was tested in measurements of pressure broadening coefficient for 811.5 nm Ar absorption line in a 40 MHz discharge in the pressure range 15-75 Torr with the help of tunable diode laser with a short external resonator. The obtained values for this coefficients reduced to 300 K are: ξ<sub>Ar-Ar</sub> = (2.85±0.1)×10<sup>-10</sup> s<sup>-1</sup>cm<sup>3</sup> for broadening in the parent gas and ξ<sub>Ar-He</sub> = (3.3±0.1)×10<sup>-10</sup> s<sup>-1</sup>cm<sup>3</sup> for broadening in helium. A good agreement with published results is observed. Measured Ar(1s<sub>5</sub>) number density amounted to 10<sup>-11</sup>cm<sup>-3</sup> for the discharge power density ~10 W cm<sup>-3</sup>.