Pulse-wave monitors

It is clear that a core-hole represents a very interesting example of an unstable state in the continuum. It is, however, also rather complicated [150]. A simpler system with similar characteristics is a doubly excited state in few-body systems, as helium. Here, it is possible [151-153] to simulate the whole sequence of events that take place when the interaction with a short light pulse first creates a wave packet in the continuum, including doubly excited states, and the metastable components subsequently decay on a timescale that is comparable to the characteristic time evolution of the electronic wave packet itself. On the experimental side, techniques for such studies are emerging. Mauritsson et al. [154] studied recently the time evolution of a bound wave packet in He, created by an ultra-short (350 as) pulse and monitored by an IR probe pulse, and Gilbertson et al. [155] demonstrated that they could monitor and control helium autoionization. Below, we describe how a simulation of a possible pump-probe experiment, targeting resonance states in helium, can be made. 

Non-invasive monitoring of blood pressure has become increasingly important in research. High-Definition Oscillometry (HDO) delivers not only accurate, reproducible and thus reliable blood pressure but also visualises the pulse waves on screen. This allows for on-screen feedback in real time on data validity but even more on additional parameters like systemic vascular resistance (SVR), stroke volume (SV), stroke volume variances (SVV), rhythm and dysrhythmia. Since complex information on drug effects are delivered within a short period of time, almost stress-free and visible in real time, it makes HDO a valuable technology in safety pharmacology and toxicology within a variety of fields like but not limited to cardiovascular, renal or metabolic research. 

We used a Thermo X7 ICPMS coupled to a New Wave Research 213 nm UV laser to determine the PGE and Au in the sulfides. Other chalcophile metals (Ag, As, Bi, Cd, Co, Cu, Fe, Ni, Pb, Re, Sb, Se, Sn, Te and Zn) were also monitored. Analytical conditions were beam size of 80 pm laser pulse rate of 10 Hz laser output power of 0.3 mJ/pulse to ablate the sulfide for 60s after a 20s gas blank was collected. Sulfide standards were used to... 

Chromite major and minor element composition was determined by microprobe. The IPGE contents of chromite were determined at UQAC by a LA-ICPMS (Thermo X7 ICP-MS coupled to a New Wave Research 213 nm UV laser, 80 pm spot diameter, 10 Hz pulse rate, 0.3 mJ/pulse power). In addition to the IPGE other elements were monitored to control the nature of ablated material and the presence of included phases. 

In the typical setup, excitation light is provided by a pulsed (e.g., nanosecond) laser (emitting in the visible range, e.g., at 532 nm, if Mb is investigated), while the probe is delivered by a continuous-wave (cw) laser. The two beams are spatially overlapped in the sample, and the temporal changes in the optical properties (such as optical absorption or frequency shift) that follow the passage of the pump pulse are registered by a detector with short response time (relative to time scale of the processes monitored), such as a fast photodiode. 

Using two pulsed tunable dye lasers, Na atoms in a beam are excited to an optically accessible ns or ml state as they pass between two parallel plates. Subsequent to laser excitation the atoms are exposed to millimeter wave radiation from a backward wave oscillator for 2-5 [is, after which a high voltage ramp is applied to the lower plate to ionize selectively the initial and final states of the microwave transition. For example, if state A is optically excited and the microwaves induce the transition to the higher lying state B, atoms in B will ionize earlier in the field ramp, as shown in Fig. 16.5. The A-B resonance is observed by monitoring the field ionization signal from state B at fB of Fig. 16.5 as the microwave frequency is swept. 

Relaxation methods can be classified as either transient or stationary (Bernasconi, 1986). The former include pressure and temperature jump (p-jump and t-jump, respectively), and electric field pulse. With these methods, the equilibrium is perturbed and the relaxation time is monitored using some physical measurement such as conductivity. Examples of stationary relaxation methods are ultrasonic and certain electric field methods. Here, the reaction system is perturbed using a sound wave, which creates temperature and pressure changes or an oscillating electric field. Chemical relaxation can then be determined by analyzing absorbed energy (acous-... 

Time-resolved spectroscopy is performed using a pump-probe method in which a short-pulsed laser is used to initiate a T-jump and a mid-IR probe laser is used to monitor the transient IR absorbance in the sample. A schematic of the entire instrument is shown in Fig. 17.4. For clarity, only key components are shown. In the description that follows, only those components will be described. A continuous-wave (CW) lead-salt (PbSe) diode laser (output power <1 mW) tuned to a specific vibrational mode of the RNA molecule probes the transient absorbance of the sample. The linewidth of the probe laser is quite narrow (<0.5 cm-1) and sets the spectral resolution of the time-resolved experiments. The divergent output of the diode laser is collected and collimated by a gold coated off-axis... 

To monitor fast events in time, firstly, a precise zero of time must be established. To that end, a femtosecond pulse is used to excite the system and initiate the dynamics. This pulse is called a pump pulse, and a nuclear wave packet is created as described... 

Femtosecond time-resolved methods involve a pump-probe configuration in which an ultrafast pump pulse initiates a reaction or, more generally, creates a nonstationary state or wave packet, the evolution of which is monitored as a function of time by means of a suitable probe pulse. Time-resolved or wave... 

Figure 2. A TRPES scheme for disentangling electronic from vibrational dynamics in excited polyatomic molecules. A zeroth-order electronic state a is prepared by a femtosecond pump pulse. Via a nonadiabatic process it converts to a vibrationally hot lower lying electronic state, p. The Koopmans-type ionization correlations suggest that these two states will ionize into different electronic continua a — a+ + e (f. ) and p — p+ + e ( 2)- When the wave packet has zeroth-order a character, any vibrational dynamics in the a state will be reflected in the structure of the Si photoelectron band. After the nonadiabatic process, the wave packet has zeroth-order p electronic character any vibrational dynamics in the state will be reflected in the 82 band. This allows for the simultaneous monitoring of both electronic and vibrational excited-state dynamics.

Figure 25. A femtosecond TRPES scheme for studying NO dimer photodissociation. A UV pump pulse creates the excited state (NO)j. Its subsequent evolution is monitored all the way from initial excitation to final product emission via a UV probe pulse, projecting the wave packet onto the ionization continuum The resulting photoelectron spectrum, reflecting vibrational and electronic changes during dissociation, is depicted in green. See color insert.

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