Femtosecond Spectroscopy of Ferroelectric Perovskites: Explanation of Anomalous Polariton Dynamics in Lithium Tantalate

1992 ◽  
Vol 293 ◽  
Author(s):  
Gary P. Wiederrecht ◽  
T. P. Dougherty ◽  
L. Dhar ◽  
K. A. Nelson
Keyword(s):  
Pulse Shaping ◽  
Stimulated Raman Scattering ◽  
Single Pulse ◽  
Lithium Tantalate ◽  
Pulse Excitation ◽  
Vibrational Modes ◽  
Temperature Dependent ◽  
Time Resolved ◽  
Optical Pulse Shaping ◽  
Impulsive Stimulated Raman Scattering

AbstractTime resolved impulsive stimulated Raman scattering (ISRS) is used to characterize the lowest frequency A1 phonon-polariton mode in lithium tantalate. The anomalously high and wavevector-dependent damping rates observed are explained in terms of coupling of the polariton to a weakly Raman-active relaxational mode and to two heavily damped vibrational modes. The dynamics of the relaxational mode are explored further through temperature dependent ISRS studies. Femtosecond optical pulse shaping is used for multiple pulse ISRS at temperatures lower than 120K where single pulse excitation led to photorefractive damage.

Dual Pump Femtosecond Laser Induced Plasma

2008 ◽  
Author(s):  
Meg Mahat ◽  
Tae Y. Choi ◽  
Nasrasadani Seifolah ◽  
Arup Neogi
Keyword(s):  
Emission Intensity ◽  
Short Pulse ◽  
Single Pulse ◽  
Atomic Emission ◽  
Dielectric Materials ◽  
Pulse Excitation ◽  
Time Resolved ◽  
Breakdown Spectroscopy ◽  
Short Pulse Laser ◽  
Ultra Short Pulse

Laser-induced breakdown spectroscopy (LIBS) can provide a noncontact way of inspecting a specimen including distinct signature of atomic composition of the sample. Ultra-short pulse laser enables characterization of any materials by utilizing the multiphoton process, which is a dominant carrier generation mechanism for dielectric materials. Additionally, femtosecond LIBS yields low background and better defined atomic lines than the nanosecond LIBS. We have performed a time-resolved emission intensity measurement for an iron oxide (Fe3O4, magnetite). The emission intensity has the peak value at 100 ps time delay, signifying that the succeeding pump beam is interacting with the plasma generated in the vicinity of the sample by the preceding beam. The dual pulses significantly enhance the atomic emission as compared to single pulse excitation and enables ultrafast time-resolved spectroscopy.

Effects of Post Calcination Treatment on Photoluminescence and Structural Properties of Scheelite-type LiEuW2O8 Nanocrystals Synthesized by Glycothermal Reaction

2006 ◽  
Vol 951 ◽  
Author(s):  
Ryo Kasuya ◽  
Tetsuhiko Isobe ◽  
Shinobu Yamao ◽  
Hocine Sfihi
Keyword(s):  
Phosphotungstic Acid ◽  
Transition Probability ◽  
Compositional Analysis ◽  
Single Pulse ◽  
Pulse Excitation ◽  
Vibrational Modes ◽  
Lithium Acetate ◽  
Convergent Beam ◽  
Calcination Treatment ◽  
The Eu

ABSTRACTThe scheelite-type LiEuW2O8 (LEW) nanoparticles of ∼50 nm in diameter were synthesized from lithium acetate, europium (III) acetate and phosphotungstic acid in 1,4-butylene glycol at 300°C for 2h by autoclave treatment. Post calcination treatment at 600°C for 2 h enhanced the photoluminescence at 465 nm due to the 4f - 4f transition excitation of Eu3+ by a factor of 24.4, and due to charge transfer (CT) excitation from either O2− or WO42− to Eu3+ by a factor of 5.8. Convergent beam electron diffractmetry and the compositional analysis revealed the non-stoichiometric structure of the scheelite-type LEW nanocrystals. Raman spectroscopy also detected the WO4 vibrational modes due to the tetragonal scheelite-type LEW. Solid-state 7Li single pulse excitation MAS NMR indicated the existence of at least three Li sites in the samples. We conclude that the following three factors are improved by calcination to increase the f-f transition probability of Eu3+: (i) a distribution of the Eu3+ – Eu3+ distance, (ii) the symmetry of Eu3+ polyhedra, (iii) the symmetry of tetrahedral WO4 units in the vicinity of Eu3+ polyhedra. Furthermore, oxygen is provided for non-stoichiometric LEW during calcination to enhance the CT probability.

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