Saturation cell, Doppler-free

The optical schematic is shown in Fig. 2. The single frequency ring dye laser is typically tuned to the crossover lines of the Doppler-free saturation cell containing sodium vapor. A wideband electro-optic modulator (e.o.) similar to the ones made by Ertmer, et al, [3] and Devoe and Brewer [15] is used to generate sidebands at 856.2 MHz, which corresponds to one half of the frequency difference between 35, 2, F = 2 to 3Pj,2, F = 3 transition and the 3S j, F = 1 to 3Pi,i, F = 2 transitions in sodium. Approximately two-thirds of the laser... 

If the laser beam is split into two partial beams which pass into opposite directions through the LMR cell, Doppler-free saturation spectra can be realized (see Sect. 2.2). This allows one to resolve even complex spectra of radicals or neutral molecules. The narrow spectral width of the Lamb-dips facilitates the determination of collisional broadening and the measurement of molecular transition moments. 

Figure ( shows the 1S-2S two-photon spectrum with its two hyperfine components, recorded in this way. Shown below is a Doppler-free saturation spectrum of Tej, observed simultaneously with the cw dye laser at the fundamental wavelength. The tellurium spectrum appears shifted by 60 MHz towards lower frequencies, since a 120 MHz acousto-optic Bragg cell is employed as a chopper. The component i is thus found in nearly perfect coincidence with the hydrogen F 1- 1 resonance. The absolute frequency of the nearby Te2 component bj has recently been measured interferometrically to within 1) parts in 10 . Using this line as a reference and taking advantage of the auxiliary Te line ii, the frequency of the centroid of the two hyperfine components was measured to be f(1S-2S)... 

If the discharge cell has windows of optical quality, it can be placed inside the laser resonator to take advantage of the -fold laser intensity (Sect. 6.2.2). With such an intracavity arrangement. Doppler-free saturation spectroscopy can also be performed with the optogalvanic technique (Sect. 7.2 and [6.101]). An increased sensitivity can be achieved by optogalvanic spectroscopy in thermionic diodes under space-charge-limited conditions (Sect. 6.4.5). Here... 

It is also possible to observe Doppler-free saturation signals in cell experiments without detecting the intensities of the transmitted laser beams. 

Returning to the field of saturation spectroscopy we note, that it is also possible to observe Doppler-free saturation signals in cell experiments without detecting the intensities of the transmitted beams. Fluorescence, opto-galvanic and opto-acoustic detection can all be used. However, since the... 

The residual Doppler width from the finite collimation ratio e of the molecular beam can be completely eliminated when nonlinear Doppler-free techniques are applied. Since collisions can generally be neglected at the crossing point of the molecular and laser beam, the lower molecular level /> depleted by absorption of laser photons can be only refilled by diffusion of new, unpumped molecules into the interaction zone and by the small fraction of the fluorescence terminating on the initial level i). The saturation intensity h is therefore lower in molecular beams than in gas cells (Example 2.3). 

A very interesting application of Doppler-free two-photon spectroscopy was demonstrated by HANSCH et al. [10.78]. The frequency w of a nitrogen laser pumped dye laser at A = 486 nm was frequency doubled in a lithium formiate monohydrate crystal. The fundamental dye laser output was used to perform saturation spectroscopy of the Balmer 3 line in a hydrogen discharge cell (see Fig.10.55), while the frequency-doubled output at X = 243 nm simultaneously excited a two-photon transition IS - 2S in a second flow cell where H atoms are produced in a gas discharge. The two-photon transition was observed through the collision-induced 2P-1S fluorescence at X = 121.5 nm. Without the Lamb shift the frequency of the 1S-2S transition should be four... 

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