Dye Lasers

Fluorescent Dyes
Dye Laser Output

Having completed and successfully running the TEA Nitrogen Laser, we can now make use of the 337nm UV pulses of laser light to pump various dyes and examine their performance as a dye Laser.

My first experience with Dye Lasers goes as far back as around 2000 when I had acquired an ex-medical Coherent 920 Argon/Dye Photocoagulator. This unit utilised the Coherent 599 Dye laser configuration.

LSI Dye Laser

In early 2021, I was lucky to secure an LSI model 337960 Nitrogen Laser with the 377121 Dye Laser Module. The Dye Laser unit arrived with the optional 1200 line/mm grating installed (the standard is a 2400 line/mm grating).

VSL-377 Laser

LSI Dye Laser

VSL-377 Laser

The following photo is of the internal configuration of the dye laser. Click on the image to view addition details.

Dye Laser Cavity

LSI Dye Laser Optics

The beam from the Nitrogen Laser (pump) enters the dye laser and is first collimated into a thin line onto the surface of a quartz cuvette which contain the dye in solution. The resonator is formed by the grating and the output coupler, in a Grazing Incidence configuration.

Dye Laser Experiments

I have acquired some small quantities of Laser grade dyes from Exciton via our local supplier, LastTek including including 7-Hydroxy-4-methylcoumarin (Coumarin 4, 456), 7-Diethylamino-4-methylcoumarin; (Coumarin 1, 47, 460) and Rhodamine 6G.

In gaining some experience with dye preparation, I prepared a small volume of Coumarin 1 and pumped the cuvette with the Nitrogen Laser. The estimated wavelength around 440nm.

N2 Pumping of Coumarin 1 Dye

N2 Pumping of Coumarin 1 Dye

In my next experiments, I prepared a volume of dye by suspending yellow highlighter dye in distilled water.

To my surprise, the first results achieved lasing threshold with the cuvette mounted in LSI Dye Laser cavity. My initial estimate of the wavelength (using an optical spectroscope and a 532nm laser as reference), was around 500-520nm. At the time I was not able to achieve lasing threshold without the resonator.

After having completed the High Voltage power supply, I conducted some further tests of the Nitrogen laser and found its output was significantly improved.

With the highlighter dye solution having been sitting for a week or so, I placed this in front of the Nitrogen Laser, and immediately achieved lasing threshold without the cavity. The Spark gap pressure was set to around 2 Bar pressure.

Measurment of Dye Laser Wavelength

On the 24th July, I calibrated and prepared the spectrometer (which takes time, and in a very dark room). The next afternoon, I undertook measurements with the Cuvette at threshold outside the resonator and then another test with the cuvette in the LSI Dye Laser resonator.

Dye Laser Spectroscopy

Dye Laser Spectroscopy

The following set of spectrograph images are results from the spectrometer measurements.

The series of mesurements include as a reference, illumination of the cuvette with 365nm 3 Watt UV LED and 405nm / 5mW Laser, which demonstrates the difference between spontaneous emission and Stimulated emission, where narrowing of the spectral line occurs.

Click on a Spectrograph to enlarge;

Spectral Curves For Dye Illuminated With 365nm UV LED. Peak Emission 526.5nm:

Yellow highlighter Dye illuminated with 365nm UV

- Flavio Spedalieri -
Written: 27th July 2021

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