H.F. Tiedje

Generation of 1.5 µJ single-cycle terahertz pulses by optical rectification from a large aperture ZnTe crystal

We demonstrate the generation muJ-level, single-cycle terahertz pulses by optical rectification from a large-aperture ZnTe single crystal wafer. Energies up to 1.5 muJ per pulse and a spectral range extending to 3 THz were obtained using a 100 Hz Ti:sapphire laser source and a 75-mmdiameter, 0.5-mm-thick, (110) ZnTe crystal, corresponding to an average power of 150 muW and an energy conversion efficiency of 3.1 x 10(-5). We also demonstrate real-time imaging of the focused terahertz beam using a pyroelectric infrared camera.

Generation of Intense Terahertz Radiation via Optical Methods

The development of new sources in the terahertz (THz) spectral region has attracted much attention over the past 20 years. In particular, the last three years have seen a surge of new laser-based techniques for generating intense, few-cycle THz pulses in the microjoule energy range, thus paving the way to the study of the nonlinear optical properties of various materials at THz frequencies. Simultaneously, innovative solutions for broad-band THz detection were found, allowing one to sense matter in the THz range with an unprecedented time resolution. In this paper, we will attempt to give a review of the properties and characteristics of the recently developed intense THz sources, with a particular eye on their potential application in ultrafast THz nonlinear spectroscopy.

Characterization of Fluorescence Lifetime of Photofrin and Delta-Aminolevulinic Acid Induced Protoporphyrin IX in Living Cells Using Single- and Two-Photon Excitation

Photodynamic therapy (PDT) is an effective treatment option for various types of invasive tumors. The efficacy of PDT treatment depends strongly on selective cell uptake and selective excitation of the tumor. The characterization of fluorescence lifetimes of photosensitizers localized inside living cells may provide the basis for further investigation of in vivo PDT dosage measurements using time-domain spectroscopy and imaging. In this communication, we investigated the fluorescence lifetime of localized Photofrin and delta-aminolevulinic acid (ALA) induced protoporphyrin IX (PpIX) in living MAT-LyLu (MLL) rat prostate adenocarcinoma cells. The MLL cells were incubated with the photosensitizers, and then treated with light under well-oxygenated conditions using a two-photon fluorescence lifetime imaging microscope (FLIM). Fluorescence lifetime images of these cells were recorded with average lifetimes of 5.5 plusmn 1.2 ns for Photofrin and 6.3 plusmn 1.2 ns for ALA-induced PpIX. When localized in cells, the lifetimes of both photosensitizers were found to be significantly shorter than those measured in organic solutions. The result for PpIX is consistent with literature values, while the lifetime of Photofrin is shorter than what has been reported. These results suggest that time-domain methods measuring photosensitizer lifetime changes may be good candidates for in vivo PDT dosage monitoring.

Optical Scanning Techniques for Characterization of Terahertz Photoconductive Antenna Arrays

Optical scanning techniques for characterizing radiation properties of terahertz photoconductive antenna arrays are proposed, and as an example, a 14-element equally spaced array structure made on low-temperature grown GaAs is characterized using the proposed methods.

Optical scanning techniques for characterization of terahertz photoconductive antenna arrays

Optical scanning methods for characterizing radiation properties of THz photoconductive antenna arrays are proposed, and as an example, a fourteen element equally spaced array structure made on low temperature grown GaAs (LT-GaAs) is characterized using the proposed methods.

Generation of High-Power Terahertz Pulses at the Advanced Laser Light Source (ALLS)

We report on terahertz pulse generation by optical rectification in a large aperture ZnTe single-crystal wafer. Terahertz pulse energies up to 0.76 muJ are measured, the highest ever observed from an optical rectification source.

High-Power Terahertz Pulses at the Advanced Laser Light Source (ALLS) Laboratory

We report on terahertz pulse generation by optical rectification in a large aperture ZnTe single-crystal wafer. Terahertz pulse energies greater than 1 μJ are measured, the highest ever observed from a ZnTe optical rectification source.

Terahertz pump-probe spectroscopy in YBCO thin films

Terahertz (THz) radiation is ideal for probing many different materials and processes. Photons in the THz regime have energies on the order of an meV, which is an important energy scale for many electronic processes. In this paper we will describe the use of optical rectification of 50 fs IR pulses to generate THz pulses. Using this method, spectrally broad THz pulses with durations on the order of ps can be produced. This feature allows us to obtain time and frequency resolved information about the transmission of THz radiation during transient processes. A 50 fs IR pulse is used to optically excite a material and the relaxation as a function of time can be observed with the THz probe. We are developing a transient THz spectroscopy to study non-equilibrium processes in thin film superconducting YBa2Cu3O7-δ (YBCO). We use ultrafast optical pulses to excite the sample, breaking a fraction of the Cooper pairs responsible for the films superconductivity. This process produces highly energetic quasiparticles which thermalize and recombine on a picosecond timescale as the superconducting state recovers. Transient THz spectroscopy allows us to follow the evolution of this process with the required resolution, while simultaneously providing valuable spectroscopic information.

Semiconductor non-linear absorption coefficients measured by optical pump with THz probe

Summary form only given. An optical pump, THz probe method is used to determine nonlinear absorption coefficients at 800 nm and 1300 nm for the semiconductors GaAs, InP, ZnSe and ZnTe. Using InP as an example, first linearly absorbed 800 nm pump light is used to determine the THz extinction cross-section per electron-hole pair. This cross-section is used to compute the free carrier density vs. 1300 nm fluence from the THz transmittance data for photon 1300 nm pump. The two photon absorption coefficient for InP at 1300 nm can then be calculated.