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By Leslie Wright
After building the Nitrogen Laser, I decided to build a dye laser attachment for it. In its simplest form, it can be nothing more than a small glass cell, and a cylinder lens! Provided of course that you have a modestly powered nitrogen laser.
The mirrors can even be left out, as often dyes will lase superradiantly! Using at least a high reflector will more than double the output at one end, and decrease divergence somewhat. The tiny emission area, and short cavity length, lead to a high divergence as lasers go, but it is nothing that cant be cured with a simple collimating lens.
Above is a picture of one of my dye lasers running superradiantly. The dye used is Rhodamine 6G, in methanol. The HR is present to boost the output power, and no OC or collimating lens is present. Note the high divergence of the output.
The choice and placement of mirrors or diffraction gratings (if you want to tune it) is important in this laser. Initially, I just had an aluminium coated HR mirror, physically pressed against one end of the cuvette, and when the laser was pushed to even a modest power it promptly blew off the aluminium coating!
There are two schemes to avoid this, either you place the mirrors far enough away, that the damage threshold of the coatings is not exceeded (and they would have to have a high radius of curvature), or you build small beam expanders between the cell and its mirrors. (this scheme is commonly used for diffraction gratings, since most of them are flat!) Most commercial designs I have seen have a highly curved OC with a beam expander arrangement between the cell and the rear diffraction grating.
Initially my cuvettes were home made, using bits of glass and either epoxy, or silicone sealant to glue them together, they were very prone to leaking, and difficult to clean so eventually I paid the 70 UK pounds for a brand new one!
A picture of my old home made cuvettes.
There is however a cheaper way, since fluorimeter cells show up on the surplus market from time to time. Normally however, these are frosted on all but two of the windows, but it is not a difficult task to polish those up, and save a fortune! See this page.
All of the glass surfaces in the cuvettes are reflective surfaces, and will create satellite beams, and contribute to poor beam quality, if they are allowed to re-enter the gain region. This is easily remedied by tilting the cell towards the HR at a slight angle, and using beam dumps to stop the reflections from escaping into the lab.
Many fluorescent dyes will lase in this cavity. I have used Rhodamine 6G (573-618nm Green-Yellow ) , Rhodamine B (599-650 Green-Red), Sodium Fluorescein (535-565nm Green-Yellow), Bromo-Flourescein (~530nm-690nm, Green to Red), Coumarin 47 (436-486nm , Blue), Nile blue (683-751nm, Red-Infra red) (expensive!)
The above quoted wavelengths are a guide! and can vary depending on type of solvent, the viscosity of the solvent, pump wavelength, dye concentration etc !
The following data came from a PDF file provided by the Lambdachrome website, before it was merged with another company.
Some of the dyes, are Carcinogenic, and most are toxic. Always use gloves, when handling dyes and solvents. DMSO will greatly enhance the skins ability to absorb a dye. It is good practice to treat all chemicals as toxic, whether they are or not.
|The following values for
are my own.
A Coumarin dye in the cavity (old Lab)
A simple binocular lens serves as the collimator!
The beam from thecoumarin dye, with glycerine based fog in the beam.
Rhodamine 6G in the cavity
And again with the fog!
Below is a view of the output (collimated) from the large polished cuvette. The dye used is Rhaodamine 6G.
Although the output is collimated, no corrective optics are used, so the spot appears as a magnified image of the emission point of the cuvette, and appears quite teardrop shaped. The yellow vertical line (although not clear in the photograph) is an image of the glass wall of the cuvette (facing the pump beam).
A profile of the beam. This is about as perfect as you can reasonably achieve, without corrective optics.