Ti-sapphire laser system

The layout of the experimental set-up is shown in Figure 8-3. The laser source was a Ti sapphire laser system with chirped pulse amplification, which provided 140 fs pulses at 780 nm and 700 pJ energy at a repetition rate of 1 kHz. The excitation pulses at 390 nm were generated by the second harmonic of the fundamental beam in a 1-nun-thick LiB305 crystal. The pump beam was focused to a spot size of 80 pm and the excitation energy density was between 0.3 and 12 ntJ/crn2 per pulse. Pump-... 

The experiments were carried out in a high vacuum chamber where a beam of atomic potassium K (4s) intersects perpendicularly with the femtosecond laser pulses leading to photoionization. The released photoelectrons are detected employing a magnetic bottle time-of-flight electron spectrometer. The 785 nm, 30 fs FWHM laser pulses provided by an amplified 1 kHz Ti sapphire laser system are split into two beams using a Mach-Zehnder interferometer. In the first experiment the time delay r is varied in a range of 80 to 100 fs with 0.2 fs resolution at a... 

We performed transient absorption measurements on BP(OH>2 with a spectrometer based on two noncollinearly phase matched optical parametric amplifiers (NOPAs) pumped by an homebuilt regenerative Ti Sapphire laser system or a CPA 2001 (Clark-MXR) [1,7]. The tunable UV pump pulses are generated by frequency doubling the output of one of the NOPAs. The other NOPA provides the visible probe pulses. The cross correlation between pump and probe pulses has a typical width (FWHM) of 40 fs. The sample is a cyclohexane solution of BP(OH)2 pumped through a flow cell with a 120 pm thick channel. 

Experiments were performed using a commercial kilohertz femtosecond Ti Sapphire laser system (Spectra Physics) delivering laser pulses at 790 nm with a duration of 110 fs and an energy of 750 pj. The pump beam at 263 nm (third harmonic) was produced by frequency doubling and sum-frequency mixing in two BBO crystals. Then, the pump beam was focused on a 300 pm thick ethylene glycol jet in order to produce electrons by photoionisation of the... 

The solutions were photolyzed by 266 nm quanta of a Nd YAG laser (FWHM < 3ns, energies up to 15 mJ) equipped with an optical absorption detection setup and by 253 nm quanta of a 10 Hz Ti Sapphire laser system generating 250 fs pulses up to 2 mJ at 253 nm. Absorption measurements were performed by the pump-probe technique. 

In short, a Ti Sapphire laser system in combination with two four-pass OPAs were used to create the femtosecond pump and probe pulses at variable wavelengths. The wavelength of the pump laser was chosen to be 530 nm for all experiments presented in the following. For the probe laser we used the fundamental output at 800 nm as well as wavelengths between 300 and 400 nm. The light scattered from the oriented single crystal samples was analyzed by a monochromator equipped with a photomultiplier tube. A more detailed description of the experimental setup is given in ref. 1. 

Overview of our new Ti—sapphire laser system, producing amplified bandwidth-limited ver a wide range of the visible spectrum. 

AT DNA double strand oligomers with sodium counterions and a length of 20 base pairs were obtained from Biotherm, and were dissolved in water and dried on a CaF2 window at 293 K in an atmosphere of 52% relative humidity (saturated solution of NaHSC. IDO at 20° Celsius [60]). This results in DNA samples with approximately 4 to 6 water molecules per base pair [37] (sample thickness 6.5 pm). It has been reported that under these conditions AT DNA oligomers adopt the B -form [35], Femtosecond time-resolved IR pump-probe experiments were performed with two independently tunable femtosecond pulses generated by parametric conversion processes pumped by a regenerative Ti sapphire laser system (800 nm, repetition rate 1 kHz, pulse duration 100 fs) [61]. The central frequency of the pump pulse was varied from 1630 to 1760 cm-1 and the probe was centred around 1650 cm-1 or 3200... 

The femtosecond transient absorption studies were performed with 387 nm laser pulses (1 khz, 150 fs pulse width) from an amplified Ti Sapphire laser system (Model CPA 2101, Clark-MXR Inc). A NOPA optical parametric converter was used to generate ultrashort tunable visible pulses from the pump pulses. The apparatus is referred to as a two-beam setup, where the pump pulse is used as excitation source for transient species and the delay of the probe pulse is exactly controlled by an optical delay rail. As probe (white light continuum), a small fraction of pulses stemming from the CPA laser system was focused by a 50 mm lens into a 2-mm thick sapphire disc. A schematic representation of the setup is given below in Fig. 7.2. 2.0 mm quartz cuvettes were used for all measurements. 

Human skin cells (keratinocytes) were tested [5] in vitro for their ability to differentiate after exposure to 0.1-3 THz radiation generated by two different pulsed Ti Sapphire laser systems. The first generated THz by directing 20 ps laser pulses onto an electro-optic... 

In early investigations, transfer times of about 100 fs or less were observed for HBT in tetrachloroethylene [16], 2-(2 -hydroxyphenyl)benzoxazole (HBO) in cyclohexane [17], and for methyl salicylate (MS) [18] and OHBA [19] in gas phase. For a number of ESIPT molecules very fast transfer times were found, even at cryogenic temperatures [20]. To resolve the evolution of the transfer and to learn about the mechanism the experimental time resolution had to be improved to better than 50 fs. Such experiments were only possible with the advent of Ti sapphire laser systems and novel nonlinear sources for ultrashort tunable light pulses. Within the last ten years several experiments with extremely high time resolution have been performed. They revealed rich spectroscopic dynamics and resulted in a detailed picture of the ESIPT and the underlying mechanisms. Their comparative discussion is the central issue of this article. 

In the experiments described here, two separate techniques have been used for interferometric characterization of the shocked material s motion frequency domain interferometry (FDI) [69, 80-81] and ultrafast 2-d spatial interferometric microscopy [82-83]. Frequency domain interferometry was used predominantly in our early experiments designed to measure free surface velocity rise times [70-71]. The present workhorse in the chemical reaction studies presented below is ultrafast interferometric microscopy [82], This method can be schematically represented as in Figure 6. A portion of the 800 nm compressed spectrally-modified pulse from the seeded, chirped pulse amplified Ti sapphire laser system (Spectra Physics) was used to perform interferometry. The remainder of this compressed pulse drives the optical parametric amplifier used to generate tunable fs infrared pulses (see below). 

In contrast to dielectrics, only a few papers were concerned with femtosecond laser processing of polymers [18, 31, 32, 57-65]. In the present review, ablation of polymer films with a Ti sapphire laser system (150 fs, 800 nm) is discussed. The results are presented in the same order as in the previous chapter for the dielectrics dependence of modification threshold on bandgap, incubation phenomena, morphology after laser illumination. 

In the TRPL measurements performed at 2K the excitation was made by a Ti sapphire laser system, with spectrally narrow (< 1 meV) 2 ps pulses. The emitted light was dispersed by a subtractive double-grating monochromator and detected with a multi-channel plate photomultiplier in the photon-counting mode with a time resolution of 20 ps. 

A commercial chirped pulse amplification (CPA) Ti sapphire laser system (Spectra Physics, Spitfire), providing linearly polarized pulses with pulse duration of 120 fs and at a wavelength of = 800 nm, was used for irradiation. The laser pulse energy was measured by means of a pyroelectric detector (Ophir, PE-9). In the fs-irradiation set-up, the sample was placed at 36° of the normal incidence in the focal plane of a 15 cm lens resulting in an elliptical laser spot on the surface. The samples were irradiated at two laser fluences (2.6 and 5.6 J/cm ) with different number of pulses (1-50 pulses)... 

Research has also been devoted to cationic two-photon photopolymerization using conventional initiator systems such as isopropylthioxanthone (ITX)/diaryl iodonium salt, with ITX serving as the photo sensitizer [45, 46]. Mode-locked operated Ti sapphire laser systems emitting femtosecond light pulses at 600, 710, or 795 nm were employed in these studies. 

Terahertz radiation can be generated with the aid of certain polymer systems that are irradiated with 800 nm pulses (duration of less than 200 fs) emitted from a Ti sapphire laser system. A prerequisite for the generation of THz radiation is the... 

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