What are Dye Lasers?
A dye laser is a type of laser that utilizes the organic dye as the active gain medium. Usually, the organic dye is a liquid solution. A dye is a colored substance that imparts (applies) its color to the material it is being applied. Most commonly used organic dyes are rhodamine (orange) that supports operation from 540-680 nm, stilbene (violet) that operates from 410-480 nm, fluorescein (green) that operates from 530–560 nm, coumarin (blue) that operates from 490–620 nm, umbelliferone (blue) that operates from 450–470 nm, tetracene, and malachite green.
Dye lasers are also classsifed into solid-state dye lasers (SSDL). In SSDL lasers, instead of a liquid solution of the dye, the gain medium is a laser dye-doped organic matrix such as poly (methyl methacrylate) (PMMA).
Dye lasers are used in astronomy (as laser guide stars), atomic vapor laser isotope separation, manufacturing, medicine, and spectroscopy applications.
Tunable dye laser
How does a dye laser work?
Energy level diagram dye laser
A dye is placed between two optically coated mirrors to form the optical cavity. When the incoming laser light focuses on the dye medium, the molecules of dye are excited into the singlet state. The singlet state is the state where the laser light is emitted by fluorescence emission. In fluorescence emission, the molecules emit the light immediately when a photon hits the dye. Now, the molecules change to their triplet state within a microsecond. In this state, the light is emitted by phosphorescence emission, and the molecules absorb the lasing wavelength, making the dye partially opaque. The light emitted from the fluorescence emission is amplified by the light pass through so many times because of the reflection between the mirrors. To allow wavelength tuning of the beam, a prism or diffraction grating is usually mounted in the beam path.
Because of the absorption in the triplet state, the high flash pump energy is needed to bring the dye past the threshold before absorption overcomes singlet emission. Hence the dye should be circulated at high speeds to keep the triplet molecules out of the beam path to operate at a small amount of input energy or reduce absorption.
Specifications of dye lasers
Wavelength: Represents the wavelength of laser light emitted from the dye laser. These lasers are available from deep UV range (50 to 100) to IR range. The wavelength is represented in a nanometer (nm).
Tunable: Represents the wavelength tune-ability of the Dye laser. These lasers are available both in tuneable and non-tuneable options. Mostly, used for tuneable purpose.
Fiber-coupled: The dye lasers are available both in fiber coupled or non-fiber coupled options.
Operation mode: Represents the operation mode. These lasers are available both in continuous wave (CW) and pulsed mode operation.
Laser color: Represents the laser colour. The dye lasers are available from deep UV to IR spectrum.
Mode: Represents the mode of operation of laser light. It can be single-mode or multi-mode.
Gain medium type: liquid/solid dye
Laser gain medium: Mostly, the organic dye rhodamine 6G is used.
Power: Represents the power output of the dye laser. It can deliver the average power range from 1 W to 2 KW range.
Pulse width: Represents the pulse duration of the dye laser working in pulsed mode of operation. The pulse width can be in femtoseconds (10−15 s), picoseconds (10−15 s) , or nanoseconds (10−9 s).
Pulse energy: Represents the energy per pulse of the dye laser working in pulsed mode of operation. Usually, it is in range of hundreds of Joules.
Polarization: Represents the polarization mode of light. The dye lasers can be horizontal/vertical polarized.
Repetition rate: Represents the number of emitted pulses per second from a dye pulsed laser .It is represented in Hz. For example, the repetition rate 10 Hz means that 10 pulses per second emitted from the pulse laser. Usually, the repetition rate of the dye laser can vary from the Hz to KHz range.
Beam diameter: Represents the beam diameter of the dye laser in mm .
Beam divergence: Represents the divergence of the laser beam. Usually, it is represented in milliradian (mrad).