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Laser facilities for laser spectroscopy of solid include "Spectra-Physics" femtosecond laser system and two "Continuum Leopard" picosecond YAG laser systems. These systems are used for transmission/reflection pump-probe optical measurements, Z-scan, Transient Grating / Four-Wave-Mixing and for Angle-Resolved Ultrafast Light Scattering measurements.
One of the two "Spectra-Physics" laser systems was recently installed in PI's lab. It consists of interconnected femtosecond and Q-switched pulsed lasers, Ti:Sapphire regenerative amplifier and computer-controlled parametric optical amplifier widely tunable in ultraviolet (UV), visible (VIS) and infrared (IR) regions. The "Spectra-Physics" laser system generates laser pulses of <35 fs duration, 7 mJ/pulse energy at 1 kHz repetition rate with unmatched pulse-to-pulse stability and provides entirely computer-controlled spectral tuning within 290-2600 nm spectral range by "TOPAS Prime" Optical Parametric Amplifier.
"TOPAS Prime" is the extension of the "Spitfire Ace" regenerative amplifier of "Spectra-Physics" system, with entirely computer-controlled spectral tuning of amplified femtosecond laser pulses. The laser system with these parameters provides substantially new research capabilities for our group to observe material dynamics at ~35 fs temporal resolution with high spectral selectivity. This system enables detailed studies of electronic dynamics and coherent lattice motion, and couplings between different degrees of freedom. The laser system generates unprecedentedly short and high-peak intensity light pulses, which is critical to conduct nondestructive experiments with clear separation between electronic and phonon dynamics of solid.
The laser system with these parameters provides exceptional research capabilities for the Lysenko's group in the area of modern ultrafast spectroscopy to observe material dynamics at sub-35 fs temporal resolution with high spectral selectivity. This enables detailed studies of coherent lattice motion, quasiparticle dynamics in superconductors, spin and electronic dynamics and coupling between these degrees of freedom. The laser system generates unprecedentedly short and high-peak intensity electromagnetic pulses, which is critical to conduct nondestructive experiments with a clear separation between electronic and phonon dynamics of solid.
Ti:Sapphire Spectra-Physics femtosecond laser system consists of "Tsunami" mode-locked Ti:sapphire laser, regenerative amplifier, parametric oscillator and autocorrelator. Mode locked pulses from Ti:Sapphire 80 MHz laser oscillator are amplified by regenerative amplifier at repetition rate 50-1000 Hz and compressed down to 130 femtosecond duration with the central wavelength λ=800 nm. The computer controlled optomechanical delay line with time resolution up to 10 femtoseconds per step has been built up on the motorized translation stage (Aerotech.Inc.).
A second "Continuum" picosecond YAG laser system is 30 ps YAG laser with similar characteristics.
This system is designed for high-resolution angular measurements of far-field light scattering within a full hemisphere, with femtosecond temporal resolution, and for sample temperatures down to a few kelvins. This newly built in our lab tr-ARHELS instrument provides substantially new information, inaccessible before, about the dynamics of stochastic surfaces on the mesoscale at low temperatures. The scatterometer uses large-scale aspherical reflective optics and modern data acquisition electronics for statistical photometric imaging of multi-scale nonequilibrium processes in materials and supports several switchable geometries. This equipment monitors a spatial distribution of scattered light with angular and temporal resolution within a hemisphere. Collinear pump and probe laser pulses are overlapped on the sample surface at normal incidence. The time delay between probe and pump pulses is controlled by an optomechanical delay line. Scattered light is collected by an elliptical metallic mirror as a function of the time delay between pump and probe pulses or as a function of sample temperature. Integrated light scattering intensity over hemisphere can be also measured by an amplified silicon detector conjugated with the gated data processor. Tr-ARHELS instrument is fully computer-controlled and operates with external ultrafast or continuous wave laser sources. It was built with the possibility to apply polarization and spectral analysis of scattered light, to realize cross-polarization ultrafast diffraction conoscopy measurements, and other experimental geometries to monitor 3D light scattering.
Tr-ARHELS Instrument Specifications:
JANIS cryostat cold finger base temperature (at the tip of the cryocooler, sample holder): 6.2 K
Diameter of the elliptical mirror: 500 mm
Angular range of measured light scattering indicatrix : Full Hemisphere. θ=5°-90°; φ=4°-356°.
Angular resolution <0.05° (Camera-1: SBIG STX-16803); <0.2° (Camera-2: Chronos-1.4)
Polarization analysis of scattered light: Cross-polarization conoscopy measurements
Optical delay line: Aerotech® PRO165LM linear motorized stage. Machine Resolution: 0.000005 mm (5 nm)
Nominal travel: 800 mm (5.3 ns maximum time delay)
A/D Converter: 16 bit
Setup Control: Wireless remote computer control
JANIS cryostat positioning (sample alignment): Wireless remote control of McAllister rotary and XYZ manipulators
Operation software: Originally written C#, C++ software for MS Windows 8, 10
Data analysis software: Originally written IgorPRO & C++, and C# software. For better performance, it requires the installation of a multiprocessor NVIDIA "Tesla K80" card for High-Performance Computing.
Z-Scan. A new optical Z-scan setup was recently built and programmed. This setup is designed to measure the real and imaginary part of the third-order nonlinear susceptibility χ(3). The setup works as a part of femtosecond and picosecond laser system.
Spectrophotometers for absorption measurements. Hitachi U-2001 automatic spectrophotometer, which permits absorption/transmission measurements, covering the wavelength range 300-1000 nm; Varian Cary-50 spectrophotometer equipped with house-built sample heater, which can be used to measure sample transmittance in the UV-visible range.
• Specialized "FluoroMax-2" luminescence spectrometer.
• Two "Triax" (Horiba-Jobin-Yvon) spectrometers. They are installed for ultrafast and CW reflection and transmission measurements and photoluminescence.
• High-resolution SPEX 1403 Ramanlog double Raman spectrometer.
This house-built equipment is designed for angle-resolved measurements of light reflection and scattering with 0.001° angular resolution. It was built and fully programmed for different types of measurement, including optical time-resolved pump-probe geometries.
Optical Cryostats
Four optical closed-cycle He cryostats with special sample mount and optical windows for spectroscopic measurements have temperature controller for precise temperature control from 3K, 7K or 10K up to 300K. The cryostats are installed for low temperature nonlinear optical measurements in most experiments.
