Home     Research     Facilities     People     Publications     OSA/Education     Jobs     UPRM Physics
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.
(a) 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.).
(b) One of the two "Continuum Leopard" YAG laser systems consists of 20 ps YAG laser and computer-controlled parametric oscillator. This laser generates pulses of 20 psec duration with wavelengths λ=1064 nm and λ=532 nm. The passive mode-locking is used in the lasing. Laser system produces exceptionally stable pulse trains at 10 Hz repetition rate. The parametric oscillator has computer-controlled tuning of wavelength.
A second "Continuum Leopard" YAG laser system is 30 ps YAG laser with similar characteristics.
These laser systems are used for several experimental methods currently equipped in the lab:
• Angle-resolved (3D) ultrafast light scattering technique;
• Time-resolved pump-probe Transient Grating/Four-Wave-Mixing;
• Time-resolved pump-probe transient reflection and transmission;
• Attenuated-total-internal-reflection technique for plasmon optics;
• Optical Z-scan;
• Luminescence and high-resolution optical spectroscopy;
• Low temperature optical and conductivity measurements techniques.
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.
Spectrophotometers for luminescence and Raman scattering measurements. Specialized "FluoroMax-2" spectrometer and "Triax" (Horiba-Jobin-Yvon) spectrometer are installed for luminescence measurements. High-resolution SPEX 1403 Ramanlog double spectrometer is aligned for Raman scattering measurements.
Optical Cryostat. JANIS cryocooler with optical cryostat has temperature controller for precise temperature control from 10 K to 300K. This cryocooler is used for low temperature nonlinear optical measurements.
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.
1. PLD system # 1. Used mainly to deposit oxide materials. Includes 4-target revolving turret with computer-controlled stepping motor for deposition of multilayers, two mass flow controllers, residual gas analyzer, and PID-controlled substrate heater capable of reaching 800°C in O2 atmosphere.
2. PLD system # 2. Dedicated for growth of nitride semiconductors. UHV main chamber with horizontally placed targets, load-lock chamber, low-energy atomic nitrogen beam source (RF N2 cracker, Mantis Deposition) for nitridation of growing films, residual gas analyzer, 4-pocket mini electron gun evaporation source (Oxford Applied Research), and PID-controlled sample heater reaching over 800°C in vacuum.
3. Sputtering system # 1: UHV chamber with a magnetron sputtering gun (Angstrom Sciences, Onix-2) powered by a pulsed-dc supply (Advanced Energy, Pinnacle Plus),.4. A smaller sputtering system houses two 2" target dc magnetron guns, substrate heater compatible with oxygen atmosphere and powered by a PID controller, gas line with two mass flow controllers (for control of gas mixtures in reactive sputtering), and a vibrating quartz microbalance to monitor film thickness. This system is mainly used as an ancillary for deposition of metallic films for electrical contacts and related fabrication.
X-ray Diffraction: High-resolution XRD system (Bruker-AXS D8 Discover). This is a 4-circle diffractometer specially configured for thin film studies. The x-ray beam line includes a parabolic multilayer x-ray mirror for increased intensity and collimation. A 4-reflection Ge crystal (2-crystal, channel-cut) monochromator can be included in the input beam line for best resolution. The goniometer is a Huber 1/4-circle Eulerian cradle, giving the system 7 independent degrees of freedom (6 sample, 1 detector). All motions are through computer-controlled steppers, allowing 0.0001° (0.36 arc-sec) resolution for θ and detector angles. Sample tilt and rotation can be controlled through -3°≤ χ ≤ 94° (with 0.001° resolution), and 360° (with 0.002° resolution), respectively. At the exit beam, a 2-reflection Ge 022 channel-cut crystal analyzer can be included. Also available is an attachment for grazing-incidence reflectometry measurements.
Electronic characterization of materials (4-point resistivity, Hall effect, etc.) can be performed in our laboratory at temperatures down to 10 K and applied magnetic fields over 1 T. The setup includes Keithley Instruments current source, nanovoltimeter, picoamperimeter, and Hall effect card and switch system, a water-cooled electromagnet with variable pole gap and 75 Amp power supply (GMW associates), a closed cycle He refrigerator (CTI), Displex cryostat (Advanced Research Systems), and cryogenic temperature controller (Lake Shore Cryotronics). This apparatus is completely computer-controlled under a house-developed LabView code. An LCR-meter allows measurements of dielectric permittivities in the frequency range from 10 Hz to 2 MHz (Quad Tech Model 7600). For measurement of piezoelectric properties of films we have a house-built electronically compensated interferometer capable of sub-Angstrom resolution.
Woollam 44-wavelength ellipsometer allows determinations of thickness and refractive index of thin films or multilayers.