To address the issue that existing intensity noise theories cannot directly simulate the intensity noise of a single-frequency laser with multiple individually pumped identical gain media in a single laser cavity, this paper corrects the laser stimulated radiation rate, which characterizes the interaction strength between the activated atoms in the gain media and the photons in the laser cavity. Based on this, the intensity noise of single-frequency Nd∶YVO₄ lasers with gain media numbers of N=1, 2, 4, corresponding to output powers of 50, 101, 140 W, respectively, were simulated using both the equivalent stimulated radiation rate model and the equivalent atomic number model. These simulation results were compared with the actual measured intensity noise of the lasers. The findings showed that, compared to the equivalent atomic number model, the equivalent stimulated radiation rate model more accurately reflects the intensity noise characteristics of single-cavity lasers with multiple gain media.

While existing intensity noise theories accurately characterize the intensity noise of lasers with a single gain medium, they do not apply to lasers with multiple gain media within a single cavity. Therefore, we propose two models: the equivalent stimulated radiation rate model and the equivalent atomic number model, to modify key parameters in the existing intensity noise theory. For lasers with multiple gain media in a single cavity, the equivalent stimulated radiation rate model is expressed as the root of the sum of the squared stimulated radiation rates for each individually pumped gain medium. Meanwhile, the equivalent atomic number model represents the pump power as the sum of the injected pump powers into each gain medium and the doping length of the gain medium as the sum of the doping lengths of each gain medium. Using these two models, we simulated the intensity noise of lasers with gain media numbers of N=1, 2, 4, corresponding to output powers of 50, 101, 140 W in a single cavity. The simulation results were then compared with the actual measured intensity noise characteristics of the lasers. By comparison, it was determined which equivalent model better reflects the intensity noise of lasers with multiple identical gain media in a single cavity.

For the case where N=1, the intensity noise spectrum of the Nd∶YVO₄ laser with an output power of 50 W at 1064 nm was stimulated using the existing intensity noise theory. The simulation results, including the resonant relaxation oscillation (RRO) frequency of 921 kHz and the cutoff frequency of 5 MHz where the laser reaches the shot noise limit (SNL), were close to the measured values of 956 kHz and 5 MHz, respectively. For the case N=2, two models—equivalent stimulated radiation rate and equivalent atomic number—were used to simulate the intensity noise spectrum of the single-frequency 1064 nm laser with an output power of 101 W. The simulated RRO frequencies were 827 kHz and 1025 kHz, and the cutoff frequencies for reaching the SNL were 4.1 MHz and 5.4 MHz, respectively. The actual measured cutoff frequency for the 101 W laser reaching the SNL was 4.3 MHz, which closely matched the 4.1 MHz obtained using the equivalent radiation model. For the case where N=4, the simulated RRO frequency and cutoff frequency for the 140 W single-frequency laser using the equivalent radiation model were 600 kHz and 2.2 MHz, which were close to the actual measured values of 593 kHz and 2.1 MHz, respectively. However, the equivalent atomic number model produced simulated RRO and cutoff frequencies of 919 kHz and 4.5 MHz, which were 1.5 times and 2.1 times the actual measured values, respectively. Compared to the equivalent radiation model, the equivalent atomic number model tends to increase the radiation of the laser, which in turn enhances the laser’s intensity noise. The simulation results based on the equivalent radiation model, however, were closer to the actual measured values and more accurately reflect the intensity noise characteristics of the laser.

To characterize the intensity noise features of lasers with multiple individually pumped identical gain media in a single cavity, we propose two models: the equivalent radiation model and the equivalent atomic number model. Using these models, the intensity noise of single-frequency Nd∶YVO₄ lasers with output powers of 50, 101, 140 W, corresponding to gain media numbers of N=1, 2, 4, were simulated. By comparing the simulation results with actual measurements reported in the literature, it was found that using the equivalent atomic number model to simulate the intensity noise of lasers with multiple identical gain media in a single cavity increases the laser radiation, resulting in enhanced intensity noise. In contrast, the equivalent simulated radiation rate model more accurately characterizes the intensity noise of lasers with multiple identical gain media, as its simulated results were much closer to the measured values. Therefore, the equivalent radiation model can effectively characterize the intensity noise of lasers with multiple identical gain media in a single cavity. This paper serves as a valuable reference for the theoretical characterization of laser intensity noise in such systems.