DYE LASERS

05.01.2013Mehmet Mustafa KARABULUT

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TABLE OF CONTENTS1. Working Principles2. CW and Pulse Modes3. Applications4. Properties5. Recent Improvements

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1. Working PrinciplesLasing medium is organic dye mixed

with a liquid solvent

Liquid solvent is generally ethyl or methyl alcohol, glycerol, or water

Wider range of wavelengths compared with gasses and solid state mediums.

Suitable for tunable lasers and pulsed lasers.

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1. Working PrinciplesThe dye solution is usually circulated

at high speeds to avoid triplet absorption

A high energy source of light is used to 'pump' the liquid

A fast discharge flash lamp or an external laser is usually used for pumping purpose

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1. Working PrinciplesMirrors are needed to oscillate the

light produced by the dye’s fluorescence

The light 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.

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2. CW and Pulse ModesDye lasers can be operated pulsed or

cw

Pulsed laser action has been obtained from very many different dyes by using one of the following pumping schemes:◦Fast and intense flashlamps, with pulse duration usually less than 100 microseconds

◦Short light pulses from another laser.

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2. CW and Pulse ModesIn both cases, the short pulse

duration serves the purpose of producing laser action before an appreciable population has accumulated in the triplet state

And before the onset of refractive-index gradients in the liquid.

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2. CW and Pulse ModesFor flashlamp pumping, linear lamps

in an elliptical-cylinder pumping chamber have been used

The liquid containing the active medium flowing through a glass tube placed along the second focal line of the ellipse.

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2. CW and Pulse Modes

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2. CW and Pulse ModesFor pulsed laser pumping, nitrogen

lasers are used, its UV output beam being suitable for pumping many dyes that oscillate in the visible range.

To obtain more energy and higher average power, the more efficient excimer lasers (in particular KrF and XeF) are being increasingly used as UV pumps

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2. CW and Pulse ModesFor dyes with emission WL longer than

550-600 nm, Nd:YAG laser or the green 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%).

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2. CW and Pulse ModesFurthermore, dye degradation due to

the pump light is considerably reduced.

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2. CW and Pulse Modes

This is a transverse pump configuration.The direction of the pump beam is

orthogonal to the resonator axis

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2. CW and Pulse Modes

The laser pump beam is focused by the lens L, generally a combination of a spherical and cylindrical lens, to a fine line along the axis of the laser cavity.

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2. CW and Pulse Modes

The length of the line focus is made equal to that of the dye

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2. CW and Pulse Modes

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

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2. CW and Pulse Modes

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

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2. CW and Pulse Modes

Tuning is achieved by rotating the mirror labeled as mirror 2.

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2. CW and Pulse ModesFor continuous laser pumping, Ar +

lasers (and sometimes also Kr+ lasers) are often used.

To achieve a much lower threshold, as required for cw pumping, the near-longitudinal pumping configuration is used.

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2. CW and Pulse Modes

The liquid dye mediumis in the form of a thin jet stream ( 200 micro mm thickness) freely flowing in a plane orthogonal to the plane of the figure and inclined at Brewster’s angle relative to the dye-laser beam direction

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2. CW and Pulse Modes

The laser beam is linearly polarized with its electric field in the plane of the figure.

For laser tuning, a birefringent filter may be inserted within the laser cavity.

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2. CW and Pulse Modes

The laser beam is linearly polarized with its electric field in the plane of the figure.

For laser tuning, a birefringent filter may be inserted within the laser cavity.

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2. CW and Pulse ModesFor femtosecond pulse generation a

colliding pulse mode locked (CPM) laser configuration is generally used

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3. ApplicationsBy virtue of their wavelength tunability, wide

spectral coverage, and the possibility of generating femtosecond laser pulses, organic dye lasers have found an important role in many fields:

Medicine: Treatment of diabetic retinopathy or treatment of several dermatological diseases

Spectroscopy: Narrow band, down to single mode, tunable source of radiation for high-resolution frequency-domain spectroscopy, or as femtosecond-pulse generators for high resolution time-domain spectroscopy

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3. ApplicationsAstronomy (as laser guide stars)

Atomic vapor laser isotope separation

Manufacturing

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4. PropertiesLaser dyes usually belong to one of

the following classes: 1. Polymethine dyes, which provide

laser oscillation in the red or near infrared .0.7–1.5 m/.

2. Xanthene dyes, whose laser operation is in the visible.

3. Coumarin dyes, which oscillate in the blue-green region (400–500 nm).

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5. Recent ImprovementsDye lasers are not widely used lasers.

Therefore there is no improvements actually.