Set Coefficients of 4 level 2 electron system for desired pumping and lasing wavelenghts


I’m trying to create & analysis a photonic crystal laser in FDTD. a clear related example(QD laser) is in the kb. in that example a 4 level 2 electron material used for active medium of laser and pumped at 1430nm with proper CW source. I have 2 main problems when i create similar structure with different pumping(532nm) and lasing(566nm) wavelengths:

1-in 4 level 2 electron system desired lasing frequency not reached( despite carefully set the omega a and omega b coefficients), what is the correct coefficients for pump at 532nm and lase in 566nm?
2- I dont know how could i plot optical gain of a laser & acquire threshold energy in FDTD

thank you,


Hi Hazhir,

It is important to note that in the KB example of the quantum dot laser, the cavity supports resonant modes at the pump and lasing frequencies. This enhances the excitation of the quantum dot and optical pumping. If you want to consider different frequencies then you would have to make sure the cavity supports resonant modes at those frequencies, otherwise it is necessary to redesign the cavity.

For looking at the optical gain you could compare the field intensity from simulations with and without the quantum dot. The lasing threshold could be measured by sweeping over pump power to find the point where the slope of the time signal changes (gain is achieved when the amplitude of the fields increase exponentially); a similar approach was used in this KB example of a cavity with linear gain.


Hi Fgomez,
many thanks for your comprehensive reply, i should say that my cavity structure is different from that one in KB example and In accordance with mode source pumping, supports resonant modes at pump( with higher Q factor) and lasing(with fewer Q factor) wavelengths but the population inversion (as shown in attached figure) did not occurred. my big problem is, sweeping over pump power because my simulation run time is 3 hour( with 8 core CPU) and actually finding threshold with this approach is impossible


Hi Hazhir,

You are welcome! In the KB example they use some tricks to achieve the lasing threshold, such as making sure the beam source is on top of the quantum dot, which should be placed where the field intensity of the cavity mode is larger. They also increase the size of the QD to artificially increase the gain. Have you tried these? If you want you can also share your simulation file and I would be happy to take a look.