Polarisation from laser

Fluorescence depolarisation by energy transfer (rather than rotational relaxation) between donor molecules of the same type can occur. Eisenthal [174] excited solutions of rhodamine 6G (9 mmol dm-3) in glycerol with 530 nm light from a frequency-doubled neodymium laser. The polarisation... 

Figure 9.22. Proton hyperfine pattern observed for the LMR transition F, N = 1, J = 3/2 F2, N" = 1, J" = 1/2, recorded using a laser line at 5 54.4 pm from CH2 F2. The numbers re fer to the value of the quantum number Mp in the lower state (M/ = —1/2 combined with Mi =+1/2 or — 1 /2). The spectrum is recorded in perpendicular polarisation (AMp = 1).

Figure 9.34. Laser magnetic resonance spectrum of CH in its a 4 state recorded in parallel polarisation (AMj = 0) with the 166.6 /un laser line of CH2F2. The rotational transition is N = 2 <—, and the quintet fine structure may be understood by reference to the energy level diagram in figure 9.33. The lines marked with an asterisk arise from an impurity species the doublet splittings of the CH lines are due to proton hyperfine interaction [69].

Figure 9.35. Laser magnetic resonance spectrum of CrH (A6E+) arising from the N = 3 - 2 rotational transition. The laser frequency was 1100.8067 GHz and the spectrum was recorded in it polarisation [70],...

An important development in microwave/optical double resonance, called microwave/optical polarisation spectroscopy, was described by Ernst and Torring [42], The principles of this technique are illustrated in figure 11.22. A linearly polarised probe beam from a tunable laser is sent through the gas sample and a nearly crossed linear polariser, before its final detection. Polarised microwave radiation resonant with a rotational transition in the gas sample is introduced via a microwave horn as shown, and resonant absorption results in a partial change in polarisation of... 

In 1960 s, CIDEP was less popular than CIDNP because CIDEP did need much faster measuring techniques than CIDNP. This is due to much faster relaxation times (usually less than 1 /r s) of polarised electron spins than those (usually a few second for protons) of nuclear spins. In 1968, Smaller et al. [2] observed a population inversion for the cyclopentyl radical with a 2-MHz ESR apparatus coupled with a 15 MeV electron beam with pulse duration of 0.5 -4.0 /z s. The response time of the system corresponded to a time constant of 1.6/z s. In 1970, Atkins et al. [3] obtained the photo-CIDEP for the ketyl radical from benzophenone in paraffin solvents with a 2-MHz ESR apparatus coupled with a 20-ns laser flash. Under favorable chemical conditions, Wong and Wan [4] demonstrated that the photo-CIDEP for some semiquinone radicals in alcohol solvents could be observed with a commercial ESR spectrometer having a 100-kHz modulation unit and a custom-designed rotating sector giving light pulses. 

Such measurements were first applied with considerable success to elastic scattering. Indeed one was able to discuss experiments which would determine all the theoretically calculable amplitudes (Bederson, 1970). For inelastic processes, such measurements necessitate the simultaneous application of spin selection techniques and the alignment and orientation measurements discussed in the previous chapter. The experiments have become feasible with the advancement of experimental techniques. The first successful differential electron impact excitation study with spin-polarised electrons and alignment and orientation measurements was performed by Goeke et al. (1983) for the e—Hg case. McClelland, Kelley and Celotta (1985, 1986) carried out a systematic study for superelastic scattering of polarised electrons from polarised laser-excited Na (3 P) atoms. This system is essentially a two-electron collision system in which spin exchange is the dominant spin-dependent interaction. It thus allows one to obtain... 

The existence of the fine-structure effect has been demonstrated for sodium (Hanne, Szmytkowski and van der Wiel, 1982 McClelland et ai, 1985 Nickich et al, 1990) using the time-reversed arrangement. A polarised electron beam is superelastically scattered from sodium atoms excited to 3 P /2 or 3 3/2 states by a single-frequency laser. McClelland et al. (1985) measured the spin asymmetry of polarised electrons that de-excite unpolarised atoms from the 3> P3/2 fine-structure state over the angular range —35° < 6 < 35°. As expected from reflection symmetry, the... 

Since the laser is highly linearly polarised with its E vector along the drift tube axes, the electrons are ejected initially towards or away from the electron detector. The ions are also ejected preferentially towards (Hf ) or away from (Hb) the ion detector. The design of the double drift tube is such that the forward and backward electrons and forward and backward ions arrive at their respective detectors with a TOP, t, given by Eq. (1) the instrumental constants, A and B, differ for electrons and ions. Hence the electron and ion TOP spectra are symmetric about their respective zero energy TOPs. 

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