Combining emission and absorption spectroscopy at rare earth spectral lines: plasma temperature measurements in ceramic metal halide lamps

The gas phase emitter effect of lanthanum within ceramic metal halide lamps and its dependence on the La vapor pressure and operating frequency

“…To ensure the power input into the arc, the lamp burner is additionally filled with 6 mg Hg, which generates an unsaturated background pressure of 2 MPa during lamp operation. 16 An adjustment of the color rendering and a generation of a gas phase emitter effect are accomplished by the addition of metal halide salts (e.g., LaI 3 and NaI) to the lamp filling. The investigated YAG-lamps are built for a nominal power input of 70 W. A sketch of the inner tube of a YAG-lamp is shown in Figure 1 and the filling properties of all investigated YAG-lamps are listed in Table I and evacuated outer bulb, which is provided with a standard lamp socket.…”

“…Radial plasma temperature distributions are measured by means of an optically thin atomic Hg double line at 576.96 nm and 579.07 nm postulating a Boltzmann population of excited states, the ideal gas law, and an additional knowledge of the constant Hg partial pressure. 8,13,16 Assuming LTE, the excitation temperature of Hg atoms corresponds to the temperature of any particle within the discharge. Radial La atom and ion density distribution are evaluated by emission spectroscopy at optically thin lines at 538.00 nm and 394.91 nm, respectively.…”

“…The undisturbed UHP backlight is determined by an interpolation of the course of UHP backlight between the wings of the absorption dip. 16 Thereby, the UHP backlight signal results from subtracting the spectral radiance emitted by the YAG-lamp from the radiance, which is measured when UHP-and YAG-lamp are operated simultaneously. Hence, the radial distribution of the line absorption coefficient is evaluated from an integration of the optical depth over frequency and a subsequent inverse Abel transformation of the lateral distribution of the integrated optical depth.…”

“…The error margin of the particle densities determined by absorption spectroscopy is in the order of 40%, but density variations are also given more accurately. 16 …”

“…Relevant cold spot temperatures of YAG-lamps seeded with DyI 3 and NaI or thulium iodide (TmI 3 ) and NaI and their relation to the electrode temperatures were determined in Ref. 16. The cold spot temperatures were obtained by comparing saturated Dy and Tm vapor pressures, which were calculated from thermodynamic data as a function of the cold spot temperature, with partial pressures of Dy and Tm, which were measured within the bulk plasma by a combination of emission and absorption spectroscopy.…”