The amplified spontaneous emission (ASE) noise has been extensively studied
and employed to build quantum random number generators (QRNGs). While the
previous relative works mainly focus on the realization and verification of the
QRNG system, the comprehensive physical model and randomness quantification for
the general detection of the ASE noise are still incomplete, which is essential
for the quantitative security analysis. In this paper, a systematical physical
model for the emission, detection and acquisition of the ASE noise with added
electronic noise is developed and verified, based on which the numerical
simulations are performed under various setups and the simulation results all
significantly fit well with the corresponding experimental data. Then, a
randomness quantification method and the corresponding experimentally
verifiable approach are proposed and validated, which quantifies the randomness
purely resulted from the quantum process and improves the security analysis for
the QRNG based on the detection of the ASE noise. The physical model and the
randomness quantification method proposed in this paper are of significant
feasibility and applicable for the QRNG system with randomness originating from
the detection of the photon number with arbitrary distributions