Ultrafast pump probe spectroscopy uses an ultrashort laser pulse split into a stronger pump beam and weaker probe beam. The pump beam excites the sample, creating a non-equilibrium state. The probe beam monitors changes in optical properties like reflectivity and transmission with femtosecond temporal resolution. Measuring these changes as the probe delay varies yields information about electronic state relaxation. Pump wavelength can selectively excite specific material modes. Ultrafast spectroscopy of quantum materials can track decay pathways from excited states to the ground state, providing insights into competing phases.

1. Ultrafast Pump Probe

2. Ultra-Fast Pump Probing
• Pump probe spectroscopy an experimental technique used to study
ultrafast electronic dynamics of particles/materials.
• An ultrashort laser pulse is split into two portions
• a stronger beam (pump) is used to excite the sample, generating a non-equilibrium
state
• a weaker beam (probe) is used to monitor the pump-induced changes in the optical
constants (such as reflectivity or transmission) of the sample material
• With time delay of pulses, fractional changes in reflectivity and transmission less
than 1/10^6 can be time resolved on femtosecond time scale
• Temporal resolution is fundamentally limited only by the pulse duration of
pump and probe pulses

3. Measuring the changes in the optical constants as a function
of time delay between the arrival of pump and probe pulses
yields information about the relaxation of electronic states in
the sample.

4. Pump
wavelength can
be varied as well,
to selectively
excite specific
modes of the
material

5. Imaging of quantum systems
• Chemists and biologists have used light pulses with femtosecond durations
to witness phenomena ranging from photo dissociation to complex
pathways in photosynthesis.
• Lately, researchers are using ultrashort laser pulses to characterize
quantum materials:
• systems in which strong electron–electron and electron–lattice interactions lead to a
multiplicity of competing phases, such as antiferromagnetic and superconductivity
• Ultrafast spectroscopic techniques can provide new insights into quantum
materials by selectively exciting collective and single particle modes of such
phases and tracking in real time their subsequent decay pathways back to
the ground state

6. Imaging quantum systems
• Ultrafast spectroscopy of quantum materials
• Pump–probe measurements can be used to obtain information on
ultrafast phenomena in quantum materials.
• Temporal resolution is fundamentally limited only by the pulse
duration of pump and probe pulses

7. Imaging quantum systems
• Competing spin, orbital, and lattice
interactions create many degenerate
ground states, and thus complex
phase diagrams.
• In such complex systems with many
competing interactions, rapid
transformation of materials to
different phases are possible.
• Ultra fast pump probing is a method
to probe materials on ultra fine time
scales

8. Imaging superconductor phase transitions
• Phase transitions to superconducting states have a signature
∆𝑅 signal
• ∆𝑅 can be used to probe superconductivity transitions
• Absorption(from pump pulse) can promote electrons to high energy
levels
• This creates a high spike in broken cooper
pairs(quasiparticles)+phonons
• Thus ∆𝑅 signal is proportional to quasiparticle densities

9. BaKFeAs superconductor
Nuh Gedik-
Used Ti:Sapphire laser pulse to
excite
Studied Ultra fast Quasiparticle
recombination dynamics to
reveal structure of
superconducting energy gap
• Know how reflectivity varies
reflectivity
• Can see relation of thermal
decay of QPs and
recombination
• Can characterize structure
of superconducting energy
gap