Stark lasers

Laser Stark (or laser electronic resonance) spectroscopy... 

Figure 9.23 Laser Stark spectroscopy with the sample inside the cavity. G, grating S, Stark electrodes W, window M, mirror D, detector...

Figure 9.24 Laser Stark spectrum of FNO showing Lamb dips in the components of the line of the ij vibrational transition. (Reproduced, with permission, from Allegrini, M., Johns, J. W. C. and McKellar, A. R. W., J. Molec. Spectrosc., 73, 168, 1978)...

Figure 9.24 shows part of the laser Stark spectrum of the bent triatomic molecule FNO obtained with a CO infrared laser operating at 1837.430 cm All the transitions shown are Stark components of the rotational line of the Ig vibrational transition, where Vj is the N-F stretching vibration. The rotational symbolism is that for a symmetric rotor (to which FNO approximates) for which q implies that AA = 0, P implies that A/ = — 1 and the numbers indicate that K" = 7 and J" = 8 (see Section 6.2.4.2). In an electric field each J level is split into (J + 1) components (see Section 5.2.3), each specified by its value of Mj. The selection mle when the radiation is polarized perpendicular to the field (as here) is AMj = 1. Eight of the resulting Stark components are shown. 

Laser Doppler anemometry data showing the axial velocity along the centerline of a 380 mm long closed chamber during the formation of acetylene/air tulip flames of different equivalence ratios. The velocity is measured 265 mm from the ignition thus, the tulip shape is already formed before the flame reaches the measurement point. This work shows the behavior similar to the results described in Figure 5.3.9. (Adapted from Starke, R. and Roth, R, Combust. Flame, 66,249,1986.)... 

Melnikov, A. V., Radu, I., Bovensiepen, U., Krupin, O., Starke, K., Matthias, F. and Wolf M. (2003) Coherent optical phonons and parametrically coupled magnons induced by femtosecond laser excitation of the Gd(OOOl) surface. Phys. Rev. Lett., 91, 227403. 

Yttrium aluminum borate, YAlj (603)4 (abbreviated to YAB), is a nonlinear crystal that is very attractive for laser applications when doped with rare earth ions (Jaque et al, 2003). Figure 7.9 shows the low-temperature emission spectrum of Sm + ions in this crystal. The use of the Dieke diagram (see Figure 6.1) allows to assign this spectrum to the " Gs/2 Hg/2 transitions. The polarization character of these emission bands, which can be clearly appreciated in Figure 7.9, is related to the D3 local symmetry of the Y + lattice ions, in which the Sm + ions are incorporated. The purpose of this example is to use group theory in order to determine the Stark energy-level structure responsible for this spectrum. 

In solid state lasers the fluorescence lines are broadened 26) by statistical Stark fields of the thermal vibrating crystal lattice and furthermore by optical inhomogenities of the crystal. The corresponding laser lines are accordinglyjlarge at multimode operation 22)... 

Instead of tuning the laser line, one can also shift the absorption lines across the laser line by Zeeman or Stark effects. This is especially advantageous in the far-infrared region where the tuning range of laser lines is restricted. 

A combination of both methods was realized by Uehara et al. 85,88) They investigated the Stark spectrum of polyatomic molecules in strong electric fields by probing the different Stark components with the Zeeman-tuned laser line. Since the molecular constants of the vibrational ground state are often known from microwave investiga-... 

Fig. 3. Stark modulation spectrum of HDCO around 2850.62 cm", obtained with a Zeeman-tuned Xe laser line at 3.50 fim. The Stark field is perpendicular to the optical field and increases from the bottom towards the top of the figure resulting in an increasing splitting of the Stark levels therefore more and more components are separated. (From Uehara, K.T., Shimizu, T., Shimoda, K., ref. 85))...

The autput of a mode-locked ruby laser 729) producing a train of pulses of 5 psec duration with a maximum peak power of 5 GW was focused into a cell pressurized with the sample gas. Pulse-energy conversion efficiencies into the Raman lines of up to 70 % have been obtained. The induced rotational lines are broadened this could be due to a strong optical Stark effect 730)... 

As a first example for the application of this technique, we mention the investigation of Stark splitting in molecules studied with a CO2 laser by Brewer etal. The authors shifted the vibration-rotation levels of by an external electric field. With increa-... 

Li, J. H., Guiltinan, M. J., and Thompson, D. B. 2006. The use of laser differential interference contrast microscopy for the characterization of starch granule ring structure. Starch-Starke 58 1-5. 

The modification of the electronic potentials due to the interaction with the electric field of the laser pulse has another important aspect pertaining to molecules as the nuclear motion can be significantly altered in light-induced potentials. Experimental examples for modifying the course of reactions of neutral molecules after an initial excitation via altering the potential surfaces can be found in Refs 56, 57, where the amount of initial excitation on the molecular potential can be set via Rabi-type oscillations [58]. Nonresonant interaction with an excited vibrational wavepacket can in addition change the population of the vibrational states [59]. Note that this nonresonant Stark control acts on the timescale of the intensity envelope of an ultrashort laser pulse [60]. 

Figure 6.9 Generic five-state system for ultrafast efficient switching. The resonant two-state system of Figure 6.6 is extended by three target states for selective excitation. While the intermediate target state 4) is in exact two-photon resonance with the laser pulse, both outer target states 3) and 5) lie well outside the bandwidth of the two-photon spectrum. Therefore, these states are energetically inaccessible under weak-field excitation. Intense femtosecond laser pulses, however, utilize the resonant AC Stark effect to modify the energy landscape. As a result, new excitation pathways open up, enabling efficient population transfer to the outer target states as well.

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