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).