A processing system comprising a processing chamber (200, 900, 1000, 1100, 1200) having a substrate holder (201, 901, 1001, 1101, 1201) for holding at least one substrate (202, 902, 1002, 1102, 1202) and a process region, the processing system configured to monitor and/or control a modification process occurring on the substrate, the processing system further comprising: at least one illuminating optical component (221, 921, 1021, 1121) within the processing chamber and configured to receive at least one generated light signal comprising at least one element-specific spectral linewidth corresponding to at least one atomic element, and direct at least one probing beam through the process region without intersecting the substrate, in response thereto; at least one corresponding receiving optical component (222, 922, 1022, 1122, 1222) within the processing chamber and configured to receive said at least one probing beam after it has passed through the process region and output at least one resultant light signal in response thereto, the at least one resultant light signal being reflective of an amount of atomic absorption by said at least one atomic element in the process region, in response to said at least one element-specific spectral linewidth of the generated light signal; an optical processing module (210, 1210) comprising: a light emission sub-module configured to output the at least one generated light signal, which is received by said at least one illuminating optical component; and an optical detection sub-module (212, 1212) configured to receive said at least one resultant light signal from the at least one receiving optical component; a processor (227, 230) coupled to at least the optical detection submodule and configured to determine, based on said at least one resultant light signal, an amount of said at least one atomic element in the process region, the at least one resultant light signal is reflective of a combined amount of atomic absorption and spontaneous atomic emission; and characterized in that the processor (227, 230) is configured to compensate for a spontaneous atomic emission component of the resultant light signal, when determining the amount of the at least one atomic element in the process region. at least one illuminating optical component (221, 921, 1021, 1121) within the processing chamber and configured to receive at least one generated light signal comprising at least one element-specific spectral linewidth corresponding to at least one atomic element, and direct at least one probing beam through the process region without intersecting the substrate, in response thereto; at least one corresponding receiving optical component (222, 922, 1022, 1122, 1222) within the processing chamber and configured to receive said at least one probing beam after it has passed through the process region and output at least one resultant light signal in response thereto, the at least one resultant light signal being reflective of an amount of atomic absorption by said at least one atomic element in the process region, in response to said at least one element-specific spectral linewidth of the generated light signal; an optical processing module (210, 1210) comprising: a light emission sub-module configured to output the at least one generated light signal, which is received by said at least one illuminating optical component; and an optical detection sub-module (212, 1212) configured to receive said at least one resultant light signal from the at least one receiving optical component; a light emission sub-module configured to output the at least one generated light signal, which is received by said at least one illuminating optical component; and an optical detection sub-module (212, 1212) configured to receive said at least one resultant light signal from the at least one receiving optical component; a processor (227, 230) coupled to at least the optical detection submodule and configured to determine, based on said at least one resultant light signal, an amount of said at least one atomic element in the process region, the at least one resultant light signal is reflective of a combined amount of atomic absorption and spontaneous atomic emission; and characterized in that the processor (227, 230) is configured to compensate for a spontaneous atomic emission component of the resultant light signal, when determining the amount of the at least one atomic element in the process region.