Ultrafast laser system capable of performing 2D, vis pump-vis probe, vis pump-midIR probe spectroscopies. Our ultrafast instrumentation is based on a Ti:sapphire laser system that produces 800 nm (2.5 mJ/pulse, 1 kHz rep. rate) pulses after amplification. These amplified pulses are used to pump two optical parametric amplifiers (OPAs). One OPA is used to generate mid-infrared (IR) pulses via difference frequency generation (DFG) that serve as the probe beam in the vis pump/mid-IR probe experiments. The other OPA is used to generate tunable visible pump pulses using either sum frequency generation (SFG) or second harmonic generation (SHG). The instrument is capable to performing 2D IR and visible pump/mid-IR probe ultrafast spectroscopes. For pump-probe experiments, we can measure from ~200 fs to 8 ns, allowing us to track a large number of potentail photophysical process (electron transfer, charge transfer, energy transfer, etc). The timescale of the ultrafast system overlaps temporally with the timescale of our nanosecond instruments. Therefore, we can follow a transient signal without gaps in the timescale of the experiment. Above the laser table is an air handler that stabilizes the room temperature for optimal laser operation. Additionally, dry air is supplied to the entire laser system which is contained in a sealed environment.

Ultrafast laser system capable of performing 2D, vis pump-vis probe, vis pump-midIR probe spectroscopies.

---

Nanosecond Mid-IR Transient Absorption Instrument

Our nanosecond mid-IR system was recently built (2014) for probing free and trapped charges in thin-films. The nanosecond timescale is important due to bimolecular recombination and trapping occurring on this timescale. The system has the capability of tracking polaron and free carrier species from a few nanoseconds to several milliseconds. Such an instrument cannot be commercially purchased, and it represents the only known instrument capable of performing such measurements with a dispersive geometry. The instrument features a uniquely designed IR lamp source that serves as the probe. Additionally, the system requires little to no alignment between scans and can perform measurements in transmissive or reflective sample geometries. The pump beam can be one of several lasers positioned around the instrument depending on the wavelength and pulse duration needed. Pump wavelength ranges from vis-NIR. Fast digital acquisition allows us to instantaneously collect the entire time spectrum (ns-ms) in a signal laser shot. The probe wavelength range is 500 to 4000 wavenumbers (2500-20,000 nm). The broad range allows overlap with our NIR transient system, allowing for board transient features to be followed. The entire instrument was designed by the group’s students and represents one of our technique development projects.

Nanosecond Vis-NIR Transient Absorption/Photoluminescence Instrument

The nanosecond vis-NIR system was built concurrently with the ns-MIR system (2016). The nanosecond timescale is important due bimolecular recombination and trapping occurring on this timescale and serves as a complementary technique to our mid-IR capabilities. Being able to view ground state bleaches (GSB) and excited state absorption (ESA) allows us to correlate free carrier kinetics on the mid-IR timescale to changes in the electric state of the material we are investigating. The instrument features feedback stabilized tungsten halogen lamp source as the probe. Additionally, the system requires little to no alignment between scans and can perform measurements in transmissive or reflective sample geometries. The pump beam can be one of several lasers positioned around the instrument depending on the wavelength and pulse duration needed. Pump wavelength ranges from vis-NIR. Fast digital acquisition allows us to instantaneously collect the entire time spectrum (ns-ms) in a signal laser shot. The probe wavelength range is 300 to 2600 nm, which is with our detectionrange. The broad range allows overlap with our mid-IR transient system, allowing for board transient features to be followed in time. The entire instrument was designed by the group’s students and represents one of our technique development projects.
The instrument can also be used to measure photoluminescence of solutions and thin-films which provide valuable information regarding the emissive states of solar cell materials.

 

---

Our Lasers

Besides our ultrafast laser, we have a several other pulsed laser sources used in various instruments.

(Left) YAG laser provides 532 nm (6ns) pulses to the transient vis-NIR and Mid-IR systems. It is also used as the pump laser for our homebuilt dye lasers. The YAG can simultaneously pump multiple instruments/dye lasers.

(Middle) Nitrogen laser (337 nm) features 800 ps pulses at 1.5 mJ/pulse with a variable rep rate (5-20 Hz). It is used as a pump for a commerical dye laser, or it can directly pump our ns mid-IR or vis-NIR systems.

(Right) Dye laser  to provide tunablity to our YAG laser. The tunable range is 550-1064nm.

      

---

Steady State Spectroscopies 
Our lab features a number of steady state techniques to complement our time-resolved capabilities. These include the ability to perform temperature dependent UV-vis-NIR and mid-IR (FTIR) steady state measurements. We can measure both liquid and solid samples using a wide range of techniques (e.g. ATR, powder diffraction, variable angle, etc). Being able to record steady state spectra for all our samples is important not just for characterization, but also for normalizing transient signals.

Cooling capabilities
The need to perform temperature dependent studies requires sealed cryostat sample holders and appropriate sensors and controlling electronics with liquid nitrogen or helium transfer lines. Multiple cryostats allow for high throughput experiments to be performed. We have designed our instruments so that sample holders can be swapped between instruments, allowing us to perform spectroscopies across timescales so samples are never exposed to air.

---