Data for Multi-Watt cavity for 266 nm light in vacuum

Description

This dataset contains the data included in the manuscript "Multi-Watt cavity for 266 nm light in vacuum". It shows the performance of two investigated mirror sets in air and ultra-high vacuum. This includes power traces of locked cavities, the decay and recovery of the cavity spectrum dependent on the ambient pressure, and the change of the cavity spectrum with increasing decay.

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The data describe the performance of two sets (A and B) of mirrors in a contaminated vacuum environment, that is, in the presence of hydrocarbons originating from Viton rings and a rotary vane roughing pump. Both sets are plano-concave mirrors with a radius of curvature of r = 100 mm and a reflectivity of (99.75 +/- 0.25)% at 266 nm. They have been assembled into a cavity with a distance of 3.34 mm between the high-reflective mirror surfaces. The cavity length was adjusted using a ring piezo (Piezomechanik HPCh 150/10-5/3), which carries one of the cavity mirrors. The coupling efficiency and impedance matching are estimated from the reduction in the intensity of the reflected light when scanning over the cavity resonance. To track the cavity spectrum and to lock it to the incident beam, 10% of the transmitted light was guided by a beam splitter to the photo-detector (Thorlabs PDA10A2). The remainder of the power was detected with a power meter (Coherent Power Max) to estimate the intra-cavity power. The vacuum chamber featured a cold baffle (liquid nitrogen) and a turbo molecular pump. This allowed reducing the pressure to below 5E-10 mbar at room temperature. To clean the vacuum chamber, it was baked at UHV for one week. The cavity is stabilized via a side-of-fringe locking scheme to 50 − 75% of the peak intensity of the TEM00 mode. The overall power in the cavity was calculated from the reading of the power meter, the finesse of the cavity, and the power reduction due to the beam splitter. Pumping the cavity in vacuum below a certain pressure led to a degradation of the cavity spectrum. To observe this, the mode coupling was optimized at 10 mbar while scanning the cavity with 100 Hz over a frequency range of about 40 GHz. Then, the 266 nm laser was blocked and the cavity was evacuated to the target pressure. As soon as the beam dump was removed and the cavity is scanned again, its spectrum started to decay. This was followed by measuring the peak value of the TEM00 every second. The effect of the decay on the cavity spectrum is exemplarily shown in the folder "Mode profiles". After the decay, we measured the pressure-dependent recovery of the cavity spectrum. To do this, we blocked the incoming light, raised the pressure to the target value, and remove the beam block. Again, the behaviour of the cavity was followed by measuring the peak value of the TEM00 every second.

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