Category: lasers

We have a “new” (used) Nd:YAG pulsed laser (labelled Nd:YAG B in the photo below) that can produce up to 600 mJ of 1064 nm light in 6 ns pulses which we frequency double to 532 nm to pump our Radiant Dyes Narrowscan laser.  The dye laser has a high-power, narrow bandwidth (5 GHz), near infra-red (730-750 nm) output.

As before, the 1064nm output of the “old” Nd:YAG (labelled as Nd:YAG A) is doubled to 532 nm and the sum-frequency of the first and second harmonic is used to generate 170 mJ of 355 nm light. This third harmonic pumps the Sirah Cobra-Stretch laser (another dye laser), which outputs broadband (85 GHz) 486 nm pulses that are then doubled to 243 nm (UV).

The 243 nm UV photons can resonantly excite ground-state Positronium into the 2P state; the excited atoms can then be driven to high-n Rydberg states with our infra-red laser (see Ref 1).

The laser systems (A and B) are completely independent, so we can easily fine-tune the timing of the two and optimise the two-step excitation process.

Refs:

[1] Selective Production of Rydberg-Stark States of Positronium. T. E. Wall, A. M. Alonso, B. S. Cooper, A. Deller, S. D. Hogan, and D. B. Cassidy, Phys. Rev. Lett. 114, 173001 (2015) DOI:10.1103/PhysRevLett.114.173001.

We have set up our newest laser: a pulsed dye laser that will provide intense UV radiation with wavelength around 365 nm. We will focus this radiation to a small spot, irradiating the Ps atoms and driving two-photon transitions to Rydberg states of Ps. By retro-reflecting the UV radiation we will drive Doppler-free transitions, which will allow us to interact with a large range of atoms, covering the very wide Doppler-profile of the hot Ps atoms.

The advantage of this scheme is that we can drive the transitions to Rydberg states with narrow band pulsed dye lasers, which should allow us sufficient resolution to address individual Rydberg-Stark states when irradiating the atoms in a uniform electric field. This selective population will allow us to prepare the atoms in states ideal for manipulation with inhomogeneous electric fields, such as focussing and Rydberg-Stark deceleration.

This photo shows the fluorescence of Coumarin 102 dye (dissolved in methanol) as a laser beam (445 nm, 1.3 W cw) passes through.

The end of the laser can be seen in the right-hand side of the photo. The image shows how the blue laser beam is invisible as it passes through the air, but its path becomes beautifully clear as it traverses the dye solution.

The laser drives electronic transitions in the dye, resulting in broad-band fluorescence. The beam is considerably attenuated as the dye is strongly absorbing at this wavelength, with almost all of the energy absorbed by the solution.

We will use this dye as the gain medium in our pulsed dye laser, pumping it at 355 nm to generate pulsed laser radiation at 486 nm, to drive the 1s -> 2p transition in positronium atoms.

2014 has started with the arrival of our pulsed laser system – a Surelite Nd:YAG laser which pumps a Sirah pulsed dye laser.

Ps Spectroscopy lab, January 2014. Optical table and pulsed dye laser now installed.

We will use this dye laser for driving electronic transitions in Ps, such as the 1s – 2p transition at 243 nm. The dye laser uses coumarin 102 as the gain medium, lasing at 486 nm, which is then doubled in BBO.