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.

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).

LSI Dye Laser

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

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.

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

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.

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

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;

Fluorescence under 365nm UV

Spectral curve of yellow highlighter ink in distilled water illuminated with 365nm ultraviolet light. Spectral range ~ 500 - 580nm (80nm).

Fluorescence under 365nm UV

Spectral curve of yellow highlighter ink in distilled water illuminated with 365nm ultraviolet light. Peak emission of 526.5nm. Spectral range ~ 500 - 580nm (80nm).

Spectral Curves For Dye Illuminated With 405nm Laser Light. Peak Emission 528.8nm:

Fluorescence under 405nm Laser

Spectral curve of yellow highlighter ink in distilled water illuminated with 405nm laser light. Spectral range ~ 512 - 580nm (68nm). An interesting observation is the slight narrowing of the spectral range and steepening of curve at the shorter wavelengths.

Fluorescence under 405nm Laser

Spectral curve of yellow highlighter ink in distilled water illuminated with 405nm laser light. Spectral range ~ 512 - 580nm (68nm). Peak emission of 528.8nm.

Spectral Curves For Dye Cell Pumped With Nitrogen Laser At 337nm, Without Resonator:

Laser Output, Without Resonator

Spectral curve of yellow highlighter ink in distilled water, observed laser output with two distinct peaks.

Laser Output, Without Resonator

Spectral curve of yellow highlighter ink in distilled water. Observed emission of Peak 1 at 520.9nm.

Laser Output, Without Resonator

Spectral curve of yellow highlighter ink in distilled water, Observed emission of Peak 2 at 523.6nm.

Spectral Curves For Dye Cell Pumped With Nitrogen Laser At 337nm, with cuvette installed In LSI Dye Laser Resonator:

Laser Output with Cuvette installed in LSI Dye Laser Resonator

Spectral curve of yellow highlighter ink in distilled water.

Laser Output with Cuvette installed in LSI Dye Laser Resonator

Spectral curve of yellow highlighter ink in distilled water, Peak Laser emission at 521.2nm.

- Flavio Spedalieri -
Written: 27th July 2021

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