DYE LASERS

1. DYE LASERS 05.01.2013 Mehmet Mustafa KARABULUT

2. TABLE OF CONTENTS • WorkingPrinciples • CW andPulseModes • Applications • Properties • RecentImprovements

3. 1. WorkingPrinciples • Lasing medium is organicdye mixed with a liquidsolvent • Liquid solvent is generallyethyl or methyl alcohol, glycerol, or water • Wider range of wavelengthscomparedwithgassesandsolidstatemediums. • Suitable for tunable lasers and pulsed lasers.

4. 1. WorkingPrinciples • The dye solution is usually circulated at high speedsto avoid triplet absorption • A high energy source of light is usedto 'pump' the liquid • A fast discharge flashlamp or an external laser is usually used for pumpingpurpose

5. 1. WorkingPrinciples • Mirrors are needed to oscillate the light produced by the dye’s fluorescence • Thelight is amplified with each pass through the liquid. • A prism or diffraction grating is usually mounted in the beam path, to allow tuning of the beam.

6. 2. CW andPulseModes • Dye lasers can be operated pulsed orcw • Pulsed laser action has been obtained from very many different dyes by using one of thefollowing pumping schemes: • Fast and intense flashlamps, with pulse duration usually lessthan 100 microseconds • Short light pulses from another laser.

7. 2. CW andPulseModes • In both cases, the short pulse durationserves the purpose of producing laser action before an appreciable population has accumulatedin the triplet state • Andbefore the onset of refractive-index gradients in the liquid.

8. 2. CW andPulseModes • For flashlamp pumping, linear lamps in an elliptical-cylinder pumping chamber have been used • The liquid containing the activemediumflowingthrough a glasstube placed along the second focal line of the ellipse.

9. 2. CW andPulseModes

10. 2. CW andPulseModes • For pulsed laser pumping, nitrogen lasers are used, its UV output beam beingsuitable for pumping many dyes that oscillate in the visible range. • To obtain more energyand higher average power, the more efficientexcimer lasers (in particular KrF and XeF)are being increasingly used as UV pumps

11. 2. CW andPulseModes • For dyes with emission WL longerthan 550-600 nm, Nd:YAG laser or thegreen and yellow emissions of a copper vapor laser are being increasingly used. • For these visible pump lasers, the conversion efficiency from pump laser to dye laser output is rather higher(30-40%) than that obtained with UV laser pumping (10%).

12. 2. CW andPulseModes • Furthermore, dye degradation due to the pump light is considerably reduced.

13. 2. CW andPulseModes • This is a transverse pump configuration. • Thedirection of the pumpbeam is orthogonal to the resonator axis

14. 2. CW andPulseModes • The laser pump beamis focused by the lens L, generally a combination of a spherical and cylindrical lens, to a fineline along the axis of the laser cavity.

15. 2. CW andPulseModes • The length of the line focus is made equal to that of thedye

16. 2. CW andPulseModes • Transverse dimensions are generally less than 1mm. to tune the output wavelength within the wide emission bandwidth of a dye (30–50 nm)

17. 2. CW andPulseModes • To tune the output WL within the wide emission bandwidth of a dye (30–50 nm) diffraction grating is inserted in the laser cavity

18. 2. CW andPulseModes • Tuningis achieved by rotating the mirror labeled as mirror 2.

19. 2. CW andPulseModes • For continuous laser pumping, Ar + lasers (and sometimes also Kr+lasers) are oftenused. • To achieve a much lower threshold, as required for cw pumping, the near-longitudinalpumping configurationis used.

20. 2. CW andPulseModes • The liquid dyemediumisin the formof a thinjet stream ( 200 micrommthickness) freely flowing in a plane orthogonal to the plane of the figureand inclined at Brewster’s angle relative to the dye-laser beam direction

21. 2. CW andPulseModes • Thelaser beam is linearly polarized with its electric field in the plane of the figure. • For laser tuning, a birefringentfilter may be inserted within the laser cavity.

22. 2. CW andPulseModes • Thelaser beam is linearly polarized with its electric field in the plane of the figure. • For laser tuning, a birefringentfilter may be inserted within the laser cavity.

23. 2. CW andPulseModes • For femtosecond pulse generation acolliding pulse mode locked (CPM) laser configuration is generally used

24. 3. Applications • By virtue of their wavelength tunability, wide spectral coverage, and the possibilityof generating femtosecond laser pulses,organic dye lasers have found an important role inmany fields: • Medicine: Treatmentof diabeticretinopathy or treatment of several dermatological diseases • Spectroscopy: Narrow band, down to single mode, tunable source of radiation for high-resolution frequency-domain spectroscopy, or asfemtosecond-pulse generators for high resolution time-domainspectroscopy

25. 3. Applications • Astronomy (as laser guide stars) • Atomic vapor laser isotope separation • Manufacturing

26. 4. Properties • Laser dyes usually belong to one of the following classes: • Polymethinedyes, which provide laser oscillation in the red or near infrared .0.7–1.5m/. • Xanthenedyes, whose laser operation is in the visible. • Coumarin dyes, whichoscillate in the blue-green region (400–500 nm).

27. 5. RecentImprovements • Dyelasersare not widelyusedlasers. • Thereforethere is no improvementsactually.