Experimental Test of the Bell Inequalities

Laser Technology

The experiment requires four lasers in the UV spectral range. Specifically, we need the laser radiation at the wavelength listed in the table. Along with the wavelength, you also find the type of laser used as well as some details on the specs of the systems.

Laser necessary in this Experiment
Wavelength Usage Type Non-Linear Conv. Pulse Length Energy fund. Linewidth Remark
266 nm Excitation of Dimer Alexandrite Third-Harmonic 120 ns 1 mJ 8 MHz tunable, injection seeded
355 nm Dissociation of Dimer Ti:Sapphire Second-Harmonic 8 ns 1 mJ 100 MHz tunable. injection seeded
253.7 nm Spin Selection Ti:Sapphire Third-Harmonic 8 ns > 200 muJ < 100 MHz regenerative amplifier, timing critical
197.3 nm Photo-Ionization Ti:Sapphire Fourth-Harmonic 8 ns >60 muJ < 100 MHz regenerative amplifier, timing critical


The most stringent requirements have to be fulfilled by the Alexandrite and the Ti:Sapphire laser systems.

  • The Alexandrite laser is used to spectroscopically select only dimer within a very narrow velocity window. This increases the propability of finding both Hg atoms of one pair in the detectors. Therefore, the Alexandrite laser has to have a very narrow frequency distribution, which requires long pulses. We opted for the Alexandrite laser since it shows long laser pulses. We have successfully reduced the linewidth of our laser to < 8 MHz (see this paper).
  • A highly efficient spin analysis is necessary in order to close the loopholes associated with previous experiments. Simulations show that this is only possible if the two laser pulse arrive within a very narrow timing window, i.e. 2 nanoseconds with respect to each other. Therefore we decided to run a flashlamp pumped Ti:Sapphire laser simultaneously on two wavelengths. The exact timing is achieved using an optical delay line (see this paper or this one).


Prof. Dr. Thomas Walther

Laser und Quantenoptik
Institut für Angewandte Physik
Fachbereich 05 - Physik
Technische Universität Darmstadt
Schlossgartenstr. 7
D-64289 Darmstadt

+49 6151 16-20831 (Sekretariat)

+49 6151 16-20834




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