Letters, continued

Laser fusion energy holds promise for the energy crisis

As a long-time reader of Laser Focus World, I would like to especially congratulate you on the September issue about the energy crisis and what photonics and lasers can do (“ Photonics and the energy crisis,” September 2006, p. 69; www.laserfocusworld. com/articles/272166). You may have ignored laser-driven fusion energy because there seemed to be not much new. Please note that a contribution to the topic I submitted with George Miley appeared in your magazine 20 years ago, causing some attention (H. Hora and G.H. Miley, “New avenues to success in laser fusion,” Laser Focus 20 ( 2) 59 [1984]). You may be interested to know that the petawatt-pico-second laser pulses have now led to a unique alternative to mainstream research, possibly leading to a method of very-low-cost fusion-energy production. The research was published in December 2006 at the Australian Physics Congress in Brisbane and in the Journal de Physique IV 133, 219 (2006), “Plasma blocks from nonlinear force generated skin layer acceleration for ignition of a fusion flame in nearly uncompressed solid DT.”

 

Heinrich Hora, Emeritus Professor University of New South Wales Sydney 2052, Australia h.hora@unsw.edu.au

Earlier research demonstrated CRDS with LEDs

We read with interest your news report on the use of light-emitting diodes (LED) to perform cavity-ring-down spectroscopy (“LED approach may yield inexpensive field systems,” January, p. 41; www.laserfousworld. com/articles/282660) We believe that your readers would like to know that we first reported the use of an LED as part of a cavity-enhanced optical-absorption measurement more than

two years ago. Using a weak blue LED, we were able to detect nitrogen dioxide (NO₂), a criteria air pollutant, with a detection limit of approximately three parts per billion with 10 seconds integration. ¹ In this device, we chose to measure the phase shift, instead of the completely equivalent “ringdown time,” so as to minimize cost and maximize sensitivity.

With improvements in optical coupling, use of a brighter LED, and implementation of very-low-noise heterodyne detection techniques, we have been able to dispense with the use of a photomultiplier tube and photon-counting techniques altogether. The current version of the monitor has a detection limit of about 20 parts per trillion which is equivalent to an extinction coefficient of 0.02 mm^{– 1}. ² The monitor has also proven to exhibit great stability, showing baseline drift of less than 0.2 ppb NO₂ in 24 hours. Furthermore, the monitor has been designed to be cost-competi-tive with current technology capable of measuring ambient concentrations of NO₂ and is constructed within a standard 19 in. rack-mounted instrumentation box. We are also currently developing a version of the instrument for the measurement of particulate and aerosol concentrations.

 

Andrew Freedman

Paul L. Kebabian Center for Sensor Systems and Technology Aerodyne Research Billerica, MA af@aerodine.com

REFERENCES

1. P.L. Kebabian, S.C. Herndon, A. Freedman, “Detection of nitrogen dioxide by cavity attenuated phase shift spectroscopy,” Anal. Chem. 77, 724 (2005).

2. P.L. Kebabian, E.C. Wood, S.C. Herndon, and A. Freedman, “A practical alternative to chemi-luminescence-based detection of nitrogen dioxide: cavity attenuated phase shift spectroscopy,” Anal. Chem., submitted for publication.

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