2D-Electronic Spectroscopy (2DES) is able to extend the capabilities of pump-probe spectroscopy, allowing to monitor the time evolution of the couplings among different electronic transitions and investigate phenomena as spectral diffusion and line broadening. We have implemented a 2DES spectrometer in a pseudo-pump-probe configuration, employing two phase locked broadband pump pulses and an independent probe pulse with high temporal resolution. The two pump-pulses are generated using an original scheme, based on phase gratings.

Our setup is based on a regenerative amplifier (Coherent Legend-Elite USP). A part of the output pulse is directed to a home-built non-collinear optical parametric amplifier (NOPA). NOPA generates chirped pulses centered roughly around 600-610 nm with an asymmetric shape, possessing 60 nm FHWM. The pulses are compressed by means of a couple of chirped mirrors such as to reach a good compensation at the sample region, obtaining a final pulse duration around 12 fs.

After chirped mirror correction, the BS1 broadband 50% beam-splitter generates pump (reflected portion) and probe (transmitted one) pulses. We then introduce our new experimental scheme, capable of generating two collinear pump pulses (E1 and E2) with very good phase difference stability, allowing to get purely absorptive 2D spectra in the pseudo-pump-probe geometry. After reflection from BS1, the pump portion is focused by the spherical mirror SM4 on the phase grating PM, generating two identical replicas (E1 and E2). The two replicas are then collimated by a spherical mirror (SM3). Mirror M12 is then used to retroreflect the two beams back on the PM phase grating at a slightly different height. The mask in front of M12 ensures that only E1 and E2 are retroreflected. Once E1 and E2 are focused back on PM, a fraction of each beam is refracted on the zeroth order of the grating, generating two collinear pulses. Two couples of fused silica wedge windows (DLw1 and DLw2) are introduced in the optical path between SM3 and M12 and the mutual lateral shift is used to finely adjust and scan the coherence delay t1 between E1 and E2. After PM, E1 and E2 are re-collimated by SM4. Finally, they are separated from the incoming beam by M13, at a slightly different height. E1 and E2 are then directed towards the DL2 translation stage to adjust the population delay T. The two beams are then overlapped with the probe and focused on the sample by SM5. Reference beam generated by BS2, passes through the sample but it is not overlapped with pump and probe beams. Finally probe and reference are collected after the sample by SM6 (located at 2f with respect to the sample position), focused at the entrance of a monochromator system, frequency dispersed and imaged on two separated array detectors .