Numerical Method for Nonlinear Optical Spectroscopies: Ultrafast Ultrafast Spectroscopy

Understand

We outline a novel numerical method, called Ultrafast Ultrafast (UF$^2$), for calculating the $n^\text{th}$-order wavepackets required for calculating n-wave mixing signals.

• The method is simple to implement, and we demonstrate that it is computationally more efficient than other methods in a wide range of use cases.
• Resulting spectra are identical to those calculated using the standard response function formalism but with increased efficiency.
• The computational speed-ups of UF$^2$ come from (a) non-perturbative and costless propagation of the system time-evolution (b) numerical propagation only at times when perturbative optical pulses are non-zero and (c) use of the fast Fourier transform convolution algorithm for efficient numerical propagation.