Doppler free laser spectroscopy

In the following I shall discuss a number of recent laser experiments on two-body systems namely, hydrogen, positron urn and muonic atoms (u He). In describing these experiments I will be introducing several applications of Doppler-free laser spectroscopy and of frequency-doubled tunable radiation. I will spend first a little time on the theory of the hydrogen atom, contrasting it with that of positronium and muonium. I will then make one or two remarks about frequency calibration of Doppler-free spectra and then consider in some detail laser experiments performed in Oxford and Stanford on hydrogen. 

Extremely high laser intensities can be achieved with the pulsed systems discussed in Sect. 8.7.2. Experiments using such systems are surveyed in Sect. 9.6. A further aspect of the extreme performance achievable with laser techniques is the ultra-narrow bandwidth achievable in CW single-mode laser systems as discussed in Sect. 8.5.1. In order to benefit from this, the Doppler broadening must be eliminated. The different techniques of Doppler-free laser spectroscopy arc discussed in Sect. 9.7. Finally, the ultimate resolution achievable by laser cooling and trapping techniques is discussed in Sect. 9.8. 

Meth DR LA LM MB MW QB RA method of measurement applied to obtain the reported values double resonance experiments (MODR and RFDR, compare 2.2.1) Doppler free laser spectroscopy Laser magnetic resonance molecular beam electric resonance or molecular beam resonance with laser detection microwave spectroscopy quantum beat spectroscopy radio astronomy... 

In the same period, it was understood that the trapping of atoms by laser light might give birth to what is now called particle-trapping spectroscopy (Letokhov 19756). This would be an important supplement to the Doppler-free laser spectroscopy techniques developed earlier, namely standing-wave absorption saturation spectroscopy... 

A comprehensive review of all the work in this field is certainly beyond the scope of this presentation. In the first part, we will only attempt to gain a simplified overview of the wide variety of different techniques of Doppler-free saturation spectroscopy which have been used to date. Next we will discuss some recent advances in the development of tunable cw sources, which can extend Doppler-free laser spectroscopy into the important ultraviolet spectral region. Finally, we will briefly discuss Doppler-free... 

We have limited our discussions to Doppler-free laser spectroscopy of gaseous sample, and even here we had to ignore many interesting topics. 

However, even our limited excursion may have shown that Doppler-free laser spectroscopy is still an exciting and lively field which continues to hold many interesting challenges and opportunities. 

Wieman, C. and Hansch, T.W. (1976). Doppler-free laser polarization spectroscopy, Phys. Rev. Lett., 36, 1170-1173. 

The experimental arrangement is shown in Fig. 2.48. The output of a tunable dye laser at X = 486 nm is frequency-doubled in a nonlinear crystal. While the fundamental wave at 486 nm is used for Doppler-free saturation spectroscopy [261] or polarization spectroscopy [278] of the Balmer transition 2Si/2- P /2 the second harmonics of the laser at X = 243 nm induce the Doppler-free two-photon transition 15 i/2 25 i/2. In the simple Bohr model [279], both transitions should be induced at the same frequency since in this model v(lS-2S) = 4v(2S-4P). The measured frequency difference Av = v(lS-2S) — 4v(2S-4P) yields the Lamb shift vlCI ) = Av — 8v] 2S) — Avfs(45 i/2 4Pi/2) <5vl(45 ). The Lamb shift (5vl(2/S) is known and Avfs(45i/2-4Pi/2) can be calculated within the Dirac theory. The frequency markers of the FPI allow the accurate determination of the hfs splitting of the 15 state and the isotope shift Avis( H- H) between the 1S-2S transitions of hydrogen and deuterium (Fig. 2.38). 

The low translational temperature achieved in supersonic beams allows the generation and observation of loosely bound van der Waals complexes and clusters (Sect. 4.3). The collision-free conditions in molecular beams after their expansion into a vacuum chamber facilitates saturation of absorbing levels, since no collisions refill a level depleted by optical pumping. This makes Doppler-free saturation spectroscopy feasible even at low cw laser intensities (Sect. 4.4). 

C. Delsart, J.C. KeUer, Doppler-free laser induced dichroism and birefringence, in Laser Spectroscopy of Atoms and Molecules, ed. by H. Walther. Topics Appl. Phys., vol. 2... 

M. Kabir, S. Kasabara, W. Demtroder, A. Doi, H. Kato, Doppler-free laser poleirization spectroscopy and optictil-optical double resonance polarization spectroscopy of a large molecule naphthalene. J. Chem. Phys. 119,3691 (2003)... 

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... 

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