Accurate measurements of the ion velocity distribution function (IVDF), the ion temperature, and the ion drift velocity by laser-induced fluorescence (LIF) are only possible if the accurate laser wavelength during the wavelength scan is known, yet an absolute calibration is not easily achievable because of the non-linear characteristics of the piezo-electric actuator in a diode laser, the small mode-hop free tuning region, and uncertainty of the wavemeter. The LIF system for the Diversified Plasma Simulator (DiPS), which is a simulator for the divertor and space plasmas, is calibrated both by absolute calibration of the wavemeter and by launching diode lasers in opposite directions. In addition, the first result on the measurement of the ion temperature and the flow velocity is given.