Active laser frequency stabilization using neutral praseodymium (Pr)

TL;DR

This paper demonstrates active laser frequency stabilization using neutral praseodymium's dense spectral lines, achieving MHz-level stability and enabling UV light generation for atomic excitation applications.

Contribution

It introduces a novel method for laser stabilization leveraging praseodymium's rich spectrum, with practical locking techniques and frequency quadrupling to produce stable UV light.

Findings

Laser frequency stabilized within 1.4 MHz

Elimination of >30 MHz/h frequency drift

Generation of stable UV light at 279.635 nm

Abstract

We present a new possibility for the active frequency stabilization of a laser using transitions in neutral praseodymium. Because of its five outer electrons, this element shows a high density of energy levels leading to an extremely line-rich excitation spectrum with more than 25000 known spectral lines ranging from the UV to the infrared. We demonstrate the active frequency stabilization of a diode laser on several praseodymium lines between 1105 and 1123 nm. The excitation signals were recorded in a hollow cathode lamp and observed via laser-induced fluorescence. These signals are strong enough to lock the diode laser onto most of the lines by using standard laser locking techniques. In this way, the frequency drifts of the unlocked laser of more than 30 MHz/h were eliminated and the laser frequency stabilized to within 1.4(1) MHz for averaging times >0.2 s. Frequency quadrupling the stabilized diode laser can produce frequency-stable UV-light in the range from 276 to 281 nm. In particular, using a strong hyperfine component of the praseodymium excitation line E = 16 502.616_7/2 cm^-1 -> E' = 25 442.742_9/2 cm^-1 at lambda = 1118.5397(4) nm makes it possible - after frequency quadruplication - to produce laser radiation at lambda/4 = 279.6349(1) nm, which can be used to excite the D2 line in Mg^+.