This thesis presents a new hybrid sensor based on in-situ Laser Induced Incandescence (LII) device allowing fast response and high frequency soot measurements in a production engine. The whole setup consists of a pulsed laser system, a fast optical detector and a special, compact designed in-situ optical LII probe, which makes it possible to change the measurement location. This work proposes a calibration method to allow relating the LII readings to soot emission. To this end, the first principle approaches are first analyzed, and then a hybrid sensor is derived by data-based methods. This hybrid sensor combines information related to both the engine working conditions and the readings of the LII. Its calibration is done using only steady state values, but its performance is assessed by comparisons with the AVL Opacimeter under both steady states and transient conditions (the FTP cycle and NEDC cycle). In order to validate the dynamics of the hybrid sensor, a fast reference would be needed. Attempts to use an in cylinder 2C spectroscopy did not provide conclusive answers. However, it is known that in-cylinder pressure data can be used for modeling of engine related quantities, in particular for NOx emission. In this case a virtual soot sensor, based on piecewise principal components analysis (PCA), was designed. Although its absolute precision is limited, it provides a delay-free estimation from a given cylinder. The lagged time from combustion to LII system or Opacimeter can be easily displayed. The comparison between the model and LII measurement confirms the earlier response of hybrid sensor systems. With the help of the virtual sensor, the transient delay time of a hybrid sensor can also be calculated. Finally, a conclusion and an outlook of this work are summarized. They will aid to the further research on the evolution process of soot during LII, the measurement of transient soot and even the soot from selective cylinders.