Laser hole

Laser hole-burning experiments in the nanosecond time domain can reveal the picosecond time history of the relaxation times in an n-level system of the molecule if those relaxation times are fast (picosecond) compared to the duration of the laser saturating pulse (nanosecond). Under these circumstances, the levels of the system can be treated as photostationary states and the kinetic equations solved exphcitly for the rate constant between any two specified levels. This leisurely approach to picosecond phenomena is equally valid in the picosecond time domain. 

The second method is the laser hole-burning method. By firing the excimer laser at the parent molecular beam, the intensity of the parent molecules along the detector axis is reduced for a time equal to the pulse width (full width = 16 ns) of the laser. The reduction of the parent beam signal is due to the dissociation of the parent molecule induced by the absorption of a 193-nm photon. The laser burn hole recorded by the MCS gives an accurate measure of the velocity spread and the most probable speed (vq) of the parent molecular beam traveling from the photodissociation region to the ionizer. 

To obtain the Vq value for the parent molecular beam, the speed profile for the parent molecular beam obtained by the chopper wheel or the laser hole-burning method is fitted to an assumed number density distribution of the form f v) r exp[ —(r — Lo)V(Ai ) ], where Av is a measure of the width of the speed profile. 

Figure 3. Laser-hole-buming spectra for CSj in (a) a pure CSj beam Pq = 150Torr), (b) a CS2/Ne seeded beam (Pq = 517Torr), (c) a CSj/He seeded beam (Pq = 362 Torr), and (d) CSj/He seeded beam (upper spectrum) (Pq = 776 Torr) and laser hole-burning spectrum for ( 82)2 in CSj/He seeded beam (lower spectrum) (Po = 776 Torr). L = 84.5 cm. Taken from ref 70.

Figure 4. Upper spectrum SO2 beam pulse produced in a 20% SOj and 80% Ar seeded mixture. Lower spectrum laser hole-burning spectrum for SOj. Pq = 1465 Torr and L = 65.5 cm.

FIGURE 9.11 Fast Fourier analyses of the axial (z) and radial (x) components of the trajectory for a single ion stored at =0.785 (P =2/3) using five electrode configurations. (a,b). Model 0, ideal geometry trap (c,d), Model 1, End-cap holes (e,f), Model 2, 2x2 mm Laser holes (g,h), Model 5, 1x4 mm Fluorescence hole and (i,j), Model 8, 2x4 mm Fluorescence holes. 

We have since verified that there has been no noticeable loss of mass resolution or sensitivity for the Esquire 3000+ using a modified ring electrode that has 2x1.5 mm laser holes and a single 2 mm fluorescence hole. Mass calibration and tuning the phase between the drive frequency and the auxiliary AC were necessary to re-establish ion trap performance. Our experimental peak width (both with and without ring electrode holes) is about 0.3 Th for rhodamine 101, or about half that of the simulation. Possible reasons for this discrepancy include inaccuracies in the shapes of the model electrodes, insufficient cooling time in the model prior to ion ejection (only ca 2 ms was used to shorten the length of the simulation), or an incomplete description of the ion ejection waveform. 

According to these simulations, an 800 pm-diameter laser beam traveling through the laser holes along the y-axis will intersect ca 36% of the ion cloud. Put another way, an ion will spend about 36% of its time within the path of an 800 pm-diameter laser beam. This interpretation and, indeed, our construction of an ion cloud of 500,000 points from 50 ion trajectories, assumes that collisions provide sufficient randomization to negate the effects of starting conditions. These results indicate the photo-excitation of ions can be quite efficient. This situation contrasts with the fluorescence collection efficiency. As discussed in Section 9.7.3, fluorescence is radiated in all directions so only a small portion of the ions (ca 0.25% in our set-up) that are excited optically will emit fluorescence in the direction of the fluorescence collection hole. 

Laser hole-burning experiments 393 10. Nuclear magnetic resonance 395... 

MAGNETIC RESONANCE SPECTROSCOPY AND HYPERFINE INTERACTIONS 393 9.3. Laser hole-burning experiments... 

In contrast to the previous experiments with dilute rare-earth ions, quadrupole splittings in the ground ( F ) and excited ( Z>o) states of Eu " in the stoichiometric rare-earth compound EuPsOu were also determined by laser hole burning and optically detected... 

FIGURE 2Z22 Misregistration of laser hole to capture pad. 

Desmear laser holes and run through the electroless copper process. 

FIGURE 63.31 Small coverlay opening drilled by excimer laser. Hole diameter is 100 micrometer. (Source Shinozaki)... 

AI foil with laser hole Pd Arrays of nanoparticles with 5nm diameter Bera et al. (2003)... 

Osgood and co-workers at Columbia University (10)(21)(22) have investigated laser hole drilling in crystals of lll-V compounds simply... 

Figure 21.17 Schematic diagram showing the layered cross section of a GaAs semiconducting laser. Holes, excited electrons, and the laser beam are confined to the GaAs layer by the adjacent n- and p-type GaAlAs layers.

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