Quasi CW photoinduced absorption
Quasi steady state PIA measurments are used to map out the one photon allowed long lived excited states of materials. Using a 405 nm CW diode laser which is electrically modulated with the square wave reference output of a two phase lock-in amplifier, the absorption spectrum of the sample is measured with and without excitation. The lock-in amplifier then measures the differential signal between these states yielding the absorption spectrum of the excited state. This signal is normalised to the ground absorption of the sample and data are presented in the form differential transmission. A positive signal, indicating induced absorption (of the transient excitd state), and negative signal indicating either emission or induced transparency, usually ground state bleaching. This method is used as the first step for time resloved measurements.
Nanosecond photoinduced absorption
To measure the kinetics of the excited states formed by optical excitation, we use different systems dependent on the lifetime of the excited state species. For longer lived transients we use nanosecond excitation and record the decay of the induced spectra using a digital oscilloscope. We have aquired a new ESKPLA NL204TH Nd:YAG giving 1.5 mJ per pulse at 355 nm and 500 Hz rep rate and high shot to shot stability. Pulse width around 5 ns. We cover the UV-VIS with a dedicated fast Si photodiode and the VIS-NIR with a custom fast GaAs detector. For better signal to noise in the nanosecond time window we use a Fanium 400 SC Continuum laser, for very long time measurements we use a stabalised W lamp.
Fanium Continuum laser foreground
Second Phosphorescence spectrometer
With such heavy demand on our current phosphorescence and delay fluorescence system, we have built a second system using a 1ns gated intensified CCD camera and using the ESKPLA NL204TH Nd:YAG as the excitation source.
Bentham dual light source, Xe and W (300nm to 2.5μm)
Femto Si and GaAs fast high band width detectors
ESKPLA NL204TH Nd:YAG
Stanford computer optics 4Quick gated intensified CCD camera (1 ns) Jobin Yvon Triax 190 spectrograph
Powertran 405 nm 60 mW diode laser 20MHz modulation
Perkin Elmer 7512 digital lock-in amplifier
HP 1GHz digital osciloscope
Leybold 10K displex cryostat and Lakesure 352 controller