Continuous laser spectroscopy

Laser spectroscopy of the 1S-2S transition has been performed by Mills and coworkers at Bell Laboratories (Chu, Mills and Hall, 1984 Fee et al, 1993a, b) following the first excitation of this transition by Chu and Mills (1982). Apart from various technicalities, the main difference between the 1984 and 1993 measurements was that in the latter a pulse created from a tuned 486 nm continuous-wave laser with a Fabry-Perot power build-up cavity, was used to excite the transition by two-photon Doppler-free absorption, followed by photoionization from the 2S level using an intense pulsed YAG laser doubled to 532 nm. Chu, Mills and Hall (1984), however, employed an intense pulsed 486 nm laser to photoionize the positronium directly by three-photon absorption from the ground state in tuning through the resonance. For reasons outlined by Fee et al. (1993b), it was hoped that the use of a continuous-wave laser to excite the transition would lead to a more accurate determination of the frequency interval than the value 1233 607 218.9 10.7 MHz obtained in the pulsed 486 nm laser experiment (after correction by Danzmann, Fee and Chu, 1989, and adjustment consequent on a recalibration of the Te2 reference line by McIntyre and Hansch, 1986). 

Continuous-Wave Intracavity Dye Laser Spectroscopy Dependence of Enhancement on Pumping Power... 

Harris Continuous-Ware Intracavity Dye Laser Spectroscopy... 

Continuous wave coherent Lyman-a radiation has recently become available [85] so that laser cooling or sensitive shelving spectroscopy of magnetically trapped hydrogen atoms is coming within reach. The ability to work with a small number of atoms is of particular interest for laser spectroscopy of antihydrogen, a goal pursued by the ATRAP and ATHENA collaborations at CERN [8]. 

As mentioned in the introduction, a major advantage that Fourier transform spectroscopy has over laser spectroscopy is that it is straightforward to record the entire spectrum of a species at once. Diode lasers in the infrared are not continuously tunable and have mode gaps which can only be filled by switching diodes. Many ultraviolet lasers are not continuously tunable either. Tunable difference frequency methods and diode lasers involve much longer scan times than are necessary with a Fourier transform device. For example, the Bomem DA3.002 can scan a bandwidth of 100 or more wavenumbers in the mid-IR at a resolution of 0.005 cm-1 in less than 3 minutes. A diode laser which scans in 20 MHz steps may require more than a day to scan the same spectral region. 

Obviously, at that time Ingvar was doing experimental physics and designing new instruments for his experiments. And he has continued to work as an experimentalist and supervise experimental work in atomic beam resonance spectroscopy, laser spectroscopy and environmentally oriented applications, but theoretical work has become an increasingly large part of his scientific activity. Indeed, so much so that in a selective list of his publications that I have obtained, only theoretical publications are mentioned Also, the nuclear physics has to a large extent given way to atomic physics in his research. 

For time-resolved laser spectroscopy, pulsed dye lasers are of particular relevance due to their continuously tunable wavelength. They can be pumped by flashlamps T 1 ps to 1 ms), by other pulsed lasers, for example, by copper-vapor lasers (T 50 ns), excimer lasers T 15 ns), nitrogen lasers T = 2-10 ns), or frequency-doubled Nd YAG lasers T = 5-15 ns). Because of the short relaxation times t/, Xk — 10 s), no spiking occurs and the situation of Fig. 6.1a is realized (Vol. 1, Sect. 5.7). The dye laser pulses have durations between 1 ns to 500 ps, depending... 

Laser Spectroscopy continues to develop and expand rapidly. Many new ideas and recent realizations of new techniques based on old ideas have contributed to the progress in this field since the last edition of this textbook appeared. In order to keep up with these developments it was therefore necessary to include at least some of these new techniques in the third edition. 

In the early days of tuneable diode laser spectroscopy, as is true for many modem-day applications, the experimental set-up of a TDLAS system was comprised of a gas cell as its centrepiece. This sampled the analyte across a closed volume allowing for the control of the internal and external parameters (e.g. ambient temperature, gas pressure in the cell, etc.). Then, flow-type systems were introduced later, in which the overall configuration was modified so that the gas could be continuously exchanged in a flow through the cell, normally assisted by a pump at the exit of the cell, as shown in Section 28.2. 

We hope that high-resolution laser spectroscopy of Rydberg states of two-electron systems, which has developed rapidly within the last three years and has contributed considerably to our knowledge of the electronic structure of such states, will continue to serve this purpose. 

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