Femtosecond pump-probe spectrometer
photos: kHz repetition rate
S. Savikhin’s lab
The kHz pump-probe spectrometer occupies two tables. One to the right houses Ti:Sapphire oscillator and laser amplifier, and one on the back houses OPA, white light generator and optical detection system with home-built ultra sensitive light detectors, imaging monochromator, femtosecond opto-mechanical delay line and spinning or steady sample holder. When needed, a sample can be housed in a low temperature He cryostat and kinetics studied at temperatures as low as 10° K. Table to the right houses MHz pump-probe spectrometer.
Former graduate
student, Nara Dashdorj, is aligning the spectrometer. His left hand rests on
the corner of a box that contains laser amplifier (faraday isolator, pulse
stretcher, amplifier and pulse compressor). OPA is assembled in an orange box
that can be seen behind
Another view to the laser amplifier part of the pump-probe spectrometer.
The infrared laser pulses have peak power ~10 GW and when focused into glass plate generate white light continuum. These are still ~100 fs long pulses, but unlike the laser output their spectrum stretches over whole visible and near infrared region. On this photo white light is refocused by a lens and its spectrum is spread on the sheet of white paper using diffraction grating.
When focused in air, these pulses can generate plasma – look at the small speckle right in front of the thick glass plate in the middle of that photo.
Click here to see a movie of plasma generated when using this beam to cut aluminum foil.
Fragment of a laser table that contains optics on the sample end of the system. The box at the far end contains OPA that generates spectrally tunable pump pulses, rest of the shown optics is used to produce white light continuum (probe pulses), modulate pump beam, control polarization via computer controlled liquid crystal polarization rotator, provide controlled delay between pulses and cross both beams in a sample. The analyzing imaging monochromator is not shown.
One of the ways to use this system to study photosynthesis in natural conditions. Never done it this way…