1. Photon Physics ‘08/’09 Thijs Besseling
Dye Lasers
Photon Physics ‘08/’09
Thijs Besseling

2. Dye Laser Introduction
Organic dye dissolved in liquid as gain medium
High density gain medium
Large quantum yield
Broad emission and gain spectrum:
tunable laser output
short pulse output
- Solid and vapor dye lasers also exist
Strong absorption in ultraviolet and visible spectrum
Molecule structure: shielded form surrounding solvent: decay primarily radiative (non collisional) so very high quantum yield: ratio of radiating excited molecules to total numer of excited molecule

3. Energy levels
Singlet and triplet state, rotational & vibrational levels
Shifted excited state S1
Similar to four level laser
Intersystem crossing
Energy states comparable to atom electronic configuration
Because of rotations and vibrations: different sub levels: broadening of the spectrum
Shift in the excited state: emission has lower energy thus higher larger wave lengths

4. Absorption and emission
Ground state absorption: reduced gain at shorter wavelengths
Triplet absorption: “Flowing the dye”
Although the emission and absorption spectra are shited, because they are so broad, there is overlap:
Ground state absorption
Spontaneous emission spectrum: fluorescence spectrum
Sigma ul: Stimulated emission cross section
Triplet absorption: not inherent to the system, can be minimized or eliminated

5. Laser pumped pulsed tunable dye laser
Pumped by a Neodymium YAG laser
Freqnecy tuning by use of etalon (Fabry Perrot cavity), and rotatable grating
Or pumped by flaslamp: electric glow discharge lamp that produces extremely intense, incoherent, full-spectrum white light for very short durations
Provides tunable ultra narrow-frequency pulsed laser output
Pumped by Nd:YAG laser or by flashlamp

6. Continuous wave tunable dye laser
Three mirror cavity with thin flowing dye region: jet stream
Emission linewidth of less than 1 kHz
Mode locked dye laser: pulses as short as 6 fs
Dye flows in thin cuvette: jet stream to overcome triple state absorption
To focus the light on this thin region, it is pumped under the brewster angle
Standing wave cavity

7. Characteristics Laser wavelengths 320-1200 nm Gain bandwidth 25-30nm
Small signal gain coefficient 500/m
Single pass gain
Output power up to 109 W/pulse, up to 2 W (cw)
Most dyes are very toxic, often carcinogenic and many are corrosive
Solvent are often highly toxic and extremely flammable
- Large range, large bandwidth, high gain, ‘user unfriendly’

8. Applications Research experiments with Important for spectroscopy
Narrow-band tunable laser emission
Ultra fast optical pulses
Important for spectroscopy
Medicine
Dermatology
Reduced need by development of tunable solid-state lasers

9. Recent experiment
Micro fabricated liquid dye lasers: opto-fluidics technology
Trying to achieve complete “lab-on-a-chip” systems
Liquid dye laser on a micro-chip. Liquid not only as gain medium but also manipulated to tune the optical properties of the laser.
The small size reduced safety risk and handling problems.
Experiment: absorbance measurements -> concentration of fluids

10. Thank you!