Study of scintillators and their applications for HEP callorimeters

Team leader - Prof. Gintautas Tamulaitis

Phone: +370 615 57525, e-mail:

 

Current research activities?

  1. Study of fast nonlinear optical processes to be exploited in future radiation detectors with timing capacities of the order of 10 ps;
  2. Study of scintillators prospective for application in radiation detection with 10 ps timing by using different varieties of photoluminescence spectroscopy and pump and probe experiments in different configurations;
  3. Search for novel garnet-type materials and glass ceramics prospective as scintillators.

Field of interest within the Center?

  1. New links with CERN providing opportunities to become involved in CERN experiments, particularly CMS;
  2. Increased personal involvements of the group members in the activities at CERN;
  3. Access to additional funding to accelerate activities in the directions emerging as necessary at CERN;
  4. Enhanced attractiveness for students of the Faculty of physics and foreign PhD students and postdocs

Available resources (Instrumentation, irradiation facilities etc.)

Nonlinear optical techniques.

The setup exploits non-destructive and contactless light-induced transient grating (LITG) technique for evaluation of the diffusion coefficient (>0.1 cm2/s) and lifetime (>20 ps) of nonequilibrium carriers.

The investigation of the dominant recombination mechanism of photoexcited carriers is performed by measuring carrier lifetime dependence on photoexcitation level and/or sample temperature by using monochromatic pump and monochromatic or broad spectrum probe technique.

Main equipment

Experimental system consisting of Yb:KGW femtosecond laser (pulse duration ~200 fs, 6 W@30 kHz), two optical parametric amplifiers (OPA) continuously tunable in 650–2500 nm range (second harmonic is available), high-precision (step of 1 µm) long travel (600 mm) opto-mechanical delay stage together with imaging spectrometer coupled with NMOS linear sensor for photoluminescence and differential absorption spectra collection in a ultraviolet and visible range.

Two solid-state picosecond lasers (25 ps pulse duration for Nd:YAG and 8 ps for Nd:YLF) up to 100 mJ per pulse energy @1064nm. The second (532 nm), third (355 nm), fourth (266 nm), and fifth (213 nm) harmonics are available.

Two Nd:YAG nanosecond lasers (pulse duration of 2 and 10 ns) with a possibility to synchronize lasing with a picosecond laser pulse using electronic pulse delay generator; the setup useful for probing of long-lasting (up to 100 milliseconds) processes.

Time-correlated single photon counting setup for measuring spectrally integrated photoluminescence decay with sub-nanosecond (~200 ps) time resolution.

A closed-cycle helium cryostat (10-300K), a liquid nitrogen cryostat (78-800K), laser beam profilers and laser power meters are available.

Time-resolved photoluminescence spectroscopy

The time-resolved photoluminescence spectroscopy setup is used for luminescence measurements in UV-VIS spectral regions with picosecond time resolution. The PL spectra can be measured with delays from nanoseconds to seconds. The measurements can be performed in a wide temperature range (77-500 K) as well as a wide range of excitation power densities.

Main equipment

Excitation source:

Femtosecond laser (pulse duration 290 fs, power 6 W@100 kHz) together with optical parametric amplifier (310-1064 nm).

Luminescence registration system:

Spectrometer SP-300 coupled with streak camera (250-900 nm, time resolution 30 ps).

Accessories: Liquid nitrogen cryosystem (78-500 K).

Luminescence spectroscopy with spatial resolution

Multifunctional microscopy system WITec Alpha 300 operating in three different modes: scanning near-field optical microscope (SNOM), confocal, and atomic force microscope (AFM). The microscopic system is coupled with spectrometer equipped with a cooled CCD camera or photomultiplier.

The surface morphology and spatial distribution of luminescence parameters can be measured simultaneously using SNOM. The spatial resolution of luminescence is ~100 nm, and the spatial resolution of topography is ~200 nm.

The spatial distribution of luminescence parameters can be measured in confocal mode; the highest spatial resolution in visible is ~250 nm in-plane and ~800 nm perpendicularly to the sample surface.

The confocal and SNOM measurements can be performed in VIS-NIR spectral regions in a wide range of excitations (from kW/cm2 to MW/cm2).

Sample surface topography can be analyzed using AFM in contact mode with ~10 nm spatial resolution. The largest area of a single scan is 80×80 µm2.

Using marks on the sample surface, the images obtained in confocal spectroscopy and AFM measurements can be matched.

Main equipment

Excitation sources:

  1. CW He-Cd laser (442 nm);
  2. CW laser diodes emitting at 405 and 660 nm.

Luminescence registration systems:

  1. Spectrometer UTS-300 coupled with CCD camera (300-900 nm);
  2. Spectrometer SR-303 coupled with InGaAs CCD camera (800-2200 nm);
  3. Photomultiplier tube (185-850 nm);
  4. InGaAs detector module (1000-2050 nm).

Microscope objectives: 10× NA = 0.25; 50× NA = 0.55; 60× NA = 0.8; 100× NA = 0.9.

Luminescence spectroscopy setup

The luminescence spectroscopy setup is used for measurements in UV-VIS-NIR spectral regions under steady-state and quasi-steady-state excitation conditions (i.e. under excitation of 4-10-ns-long pulses exceeding the free carrier lifetime), or with the time resolution in nanosecond domain.

Two geometries can be used for excitation: front-surface for standard luminescence measurements, and edge-emission for the study of stimulated emission and optical gain, using variable stripe length technique.

The measurements can be performed in a wide temperature range from 8 to 300 K and under excitation intensities ranging over 9 orders of magnitude from mW/cm2 to MW/cm2.

A double monochromator with low level of scattered light, which is coupled with photomultiplier tube, is used for luminescence spectroscopy with high spectral resolution or for measuring luminescence spectra at resonant excitation within the spectral range of the measurement, while rapid routine measurements are performed using a CCD camera.

The time-resolved PL spectra with nanosecond time resolution are measured up to millisecond timescale using ICCD.

Main equipment

Excitation sources:

  1. CW He-Cd laser (325 nm);
  2. Nanosecond YAG:Nd laser and its harmonics (1064, 532, 355, 266, and 213 nm; pulse duration 4 ns; max pulse energy 250 mJ@1064 nm, 120 mJ@532 nm, 80 mJ@355 nm, 30 mJ@266 nm, 8 mJ@213 nm);
  3. Tunable wavelength laser (210-2300 nm; pulse duration 4 ns; max pulse energy: up to 5 mJ@210-420 nm, up to 30 mJ@420-2300 nm).

Luminescence registration systems:

  1. Double monochromator HRD-1 coupled with photomultiplier tube (160-930 nm);
  2. Spectrometer SR-500 coupled with ICCD (180-850 nm, time resolution 2 ns);
  3. Spectrometer SR-303 coupled with InGaAs CCD (800-2200 nm).

Accessories:

  1. Closed-cycle helium cryosystem (8-300 K);
  2. Laser power and energy meters;
  3. Fiber couplers to spectrometers.

Measurement of luminescence efficiency

An integrating sphere by SphereOptics is used for measuring external photoluminescence quantum efficiency. The interior surface of the sphere is covered with BaSO4 and is highly reflective in the range from 350 to 1000 nm. Monochromized xenon lamp light is used for photoluminescence excitation, the sphere is coupled with a Hamamatsu spectrometer for light registration.