#  Nonlinear Optics 

 



The high peak electric fields of ultrafast laser pulses offer a powerful means to probe optical nonlinearities in quantum materials, revealing unique insights into material symmetries, electronic wavefunctions, and states inaccessible to linear optical probes. Our group specializes in generating and detecting intense, frequency-tunable laser pulses spanning the visible, infrared, and far-infrared spectrum (2 eV to the THz regime).

Using difference frequency generation (DFG) between femtosecond near-infrared pulses produced by two synchronized three-stage optical parametric amplifiers (OPAs), we generate mid-infrared pulses ranging from 5 to 60 THz. To ensure phase coherence, the OPAs are seeded with the same white-light continuum, maintaining carrier-envelope phase stability of the generated pulses. Through chirped-pulse DFG, we produce picosecond, Fourier transform-limited pulses with narrow bandwidth, enabling high spectral resolution for precise investigations of resonant responses in quantum materials.

   ![OPA photo](/sites/g/files/omnuum1256/files/styles/hwp_1_1__720x720_scale/public/2024-12/IMG_0311%20%281%29.jpg?itok=Mlqs-cSo) 

 

Fig. 1: *Non-collinear optical parametric amplifier (NOPA) and optical parametric amplifier (OPA) stages in the Astrella Ti:Sapphire laser table.*For lower-energy excitations, we generate intense THz pulses via optical rectification (OR) in organic crystals such as DAST, DSTMS, BNA, and OH1. These pulses, along with those in the mid-infrared, are critical for resonantly driving optically active modes and manipulating complex condensed matter systems under strong light excitation. Furthermore, their high intensity and tunability make them ideally suited for advanced spectroscopic techniques, such as second and third harmonic generation, providing deeper insights into nonlinear material properties

   ![lab_spectra](/sites/g/files/omnuum1256/files/styles/hwp_1_1__720x720_scale/public/2025-08/PtW_Harvard_Mitrano_lab_wavelengths_Final.png?itok=poV5U0X9) 

 

Fig. 2: *Range of tunable femtosecond pulses generated in the Mitrano Lab. WL - white light; Ti:Sa – Ti:sapphire; OPA SIG - optical parametric amplifier (OPA) signal; OPA IDL – OPA idler; MIR DFG – mid-infrared difference frequency generation; FIR DFG – far-infrared difference frequency generation.*