Femtosecond Laser Spectroscopy

Femtosecond laser spectroscopy

Room 61

Our ultrafast laser labratories include a femtosecond laser system which allows us to investigate the dynamics of photoexcitations on a temporal scale from 250 fs up to 4 ns. This system is based around a

Coherent Mira-900f  Ti:Sapphire laser oscillator and RegA-9000  amplifier. This provides access to 250fs, 4 µJ, pulses of 100kHz repetition rate at 1.60eV which is used as a starting point in two of our primary experiments.

Pump-probe spectroscopy

Pump-probe spectroscopy involves the use of two temporally displaced ultrafast laser pulses; one to excite a sample termed ‘pump’, and other to probe the absorption of the photoexcitations generated by the pump. In this case both pump and probe pulses come from a Coherent OPA-900 which is used to produce a variety of outputs, including a second-harmonic beam at 3.2eV, a single wavelength output (1.72-2.79eV), a white-light supercontinuum (1.24-2.70eV) and an Idler output (0.94-2.4µm). The relative time delay between the two pulses is controlled by a mechanical delay stage. With this system we can directly investigate the dynamics of singlet excitons, charge-transfer and polaron states within a single experiment. Our system also can be used to measure the triplet yield of our polymers, and can be used in conjunction with a closed-cycle Helium cryostat to provide access to measurement temperatures down to 5K.

This system is used for 3 key experiments;

White light continuum pump-probe

Basic measurement of transient speciies formed after excitation 250 fs

Single wavelength femtosecond decay measurements

Using lock-in techniques to give the highest dynamic range decay measurements 200 fs

Degenerate wavelength femtosecond Ground State Recovery

Used to determine Inter system crossing rates, triplet exciton and polaron pair yields 250 fs

Femtosecond up-conversion

Details on our femtosecond up-conversion setup can be found at this link.

Coherent Mira 900F Ti:Sapphire Coherent Verdi X pump laser

Coherent Rega Ti:Sapphire amplifier Coherent 9650 OPA (400 to 2000 nm) Coherent/APE sync pumped OPO

Dual deep well Ocean Optics detectors Dual NIR Ocean Optics linear array detectors

Jobin Yvon Gemmini double additive monochromator Electron tubes Solar blind photon counting PMT

Stanford RF lock-in amplifier

Newport IMS 600 delay line Newport URM80 rotation stage Conoptics EO modulator system

Cryomech ST405 3K pulse tube cryostat

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