The setup generates ultrafast pulses (640–950 nm) using a laser and OPA with compression, splits them into four phase-stabilized beams via AOMs, and controls delays (τ, T,  t). A pulse shaper optimizes pulses before exciting a sample at ~5 K. Heterodyne detection with balanced photodetection and lock-in amplification enables sensitive measurement of coherent nonlinear optical responses, revealing excitonic dynamics in semiconductor nanostructures. 

We investigate coherent interactions between optical excitations in semiconductor nanostructures using ultrafast laser pulses. Our primary tool is two-dimensional Coherent Spectroscopy (2DCS), a powerful technique that provides detailed insights into the dynamics and coupling of excitonic states. By combining a custom-built experimental setup with advanced numerical simulations, we aim to study, manipulate, and engineer coherent phenomena in semiconductor systems. This integrated approach allows us to explore many-body effects, quantum coherence, and dephasing mechanisms with high temporal and spectral resolution, paving the way for applications in optoelectronics and quantum information science (QIS). 

The setup shown is a classic 4f pulse shaper utilizing a pair of diffraction gratings and plano-convex lenses. The input femtosecond pulse is first dispersed spatially by the first grating into its spectral components. These components are then collimated and focused by a plano-convex lens onto the Fourier plane, where spectral phase and amplitude can be modulated (e.g., via a spatial light modulator or mask). The second plano-convex lens and grating recombine the spectrally modulated components, producing a temporally shaped output pulse. This configuration allows precise manipulation of ultrafast pulses in both amplitude and phase domains, essential for coherent control and multidimensional spectroscopy experiments. 

4f optical setup for femtosecond pulse modulation 

The electric field of a transform-limited Gaussian pulse centered around zero time delay. This pulse exhibits a symmetric temporal profile, indicating that all frequency components are in phase — hence, there is no chirp. 

The chirped pulse represents a linearly chirped Gaussian pulse. The envelope remains Gaussian, but the instantaneous frequency varies with time — increasing monotonically from red to blue across the pulse duration. This linear chirp is evident from the changing frequency (color-coded) within the pulse, indicating a quadratic phase modulation in time.