Rhodamine - 6g (or) Xanthene Dye Laser

RHODAMINE ‒ 6G (OR) XANTHENE DYE LASER

Characteristics of Rhodamine - 6G Dye laser

Type: Dye Laser

Active medium: Organic Dyes such as Rhodamine‒6G (or) Xanthene dissolved in solvents like Water (or) Alcohol.

Active Centre: Rhodamine‒6G (or) Xanthene dye.

Pumping method: Optical Pumping

Pumping Source: Flash lamp (or) another laser like N₂ laser (or) argon‒ion laser

Optical Resonator: Resonant cavity consisting of diffraction grating at one end and a partially reflective mirror on the other end.

Power output: 5.6 to 6.5 watts. (Upto 320mW on tuning)

Output Wavelength: Yellow to Red region (upto 500Å on tuning)

Nature of Output: Both Pulsed and Continuous waves.

Principle

Organic dye such as Rhodamine‒6G (or) Xanthene dye dissolved in solvents like water or alcohol is placed in the Dye cell. The pumping source excites these Dye molecules to excited state. After achieving population inversion, these molecules emit photons of the same wavelength, leading to laser action.

Construction

Liquid solution of Rhodamine‒6G (or) Xanthene organic dye dissolved in a solvent such as water or alcohol is placed in the Dye cell as shown in Fig 10.20.

Strong light source such as flash lamp (or) lasers like N₂ laser (or) Argon‒ ion laser act as a pumping source to excite the Xanthene molecules.

A tuning plate is used for better tuning of laser wavelength and hence these lasers are also called as Tunable Lasers.

For better tuning, one of the mirrors of the resonant cavity is replaced by diffraction grating. Thus, in dye lasers the optical resonator consists of diffraction grating at one end and the partially reflective mirror at the other end.

Working

Strong light source like Flash lamp (or) argon‒ion laser (Blue‒Green Laser) is switched ON.

This light passes through the Rhodamine‒6G (or) Xanthene organic dye molecules kept inside the Dye cell and excite these molecules to the excited state.

The excited dye molecules spontaneously emit photons, and some of these photons stimulate other excited molecules to emit photons of the same wavelength, which leads to laser action.

These photons are reflected back and forth between the diffraction grating and the partially reflecting mirror i.e., through the optical resonator and thus amplified.

Now, with the help of tuning plate and by rotating the diffraction grating at different angles, we can produce laser of different wavelength even upto 500Å and due to this reason, dye lasers are also called tunable lasers.

For tunable Lasers, the angle of diffraction (θ) must satisfy the following condition, viz.,

 2d sineθ = nλ (n = 1, 2, 3, ...)

Where

d is the grating spacing.

and λ is the wavelength of radiation.

Thus the amplified laser from the dye cell & optical resonator is emitted through the partial mirror and the wavelength of the emitted light falls in the yellow‒red region.

Here, we can observe that, when the light of wavelength in Blue‒Green region is passed through the Dye laser, it emits the laser light in Yellow‒Red region.

NOTE: Dye lasers operate without the intervening of metastable state.

Advantages

(i) Dye lasers possess wide range of tunable wavelengths and hence it is used for various applications.

(ii) These lasers will achieve very high power output in both pulsed and continuous wave modes.

(iii) The dye lasers will have high repetition rates and will allow efficient cooling.

Disadvantages / Limitations

(i) Dye molecules will degrade in due course of time and hence the lifespan of Dye laser is less.

(ii) The experimental setup for Dye laser is complex in nature and hence maintenance cost will be high.

Applications

(i) Dye lasers are widely used in spectroscopy for the study of properties of materials.

(ii) In Astronomy, dye lasers are used to create artificial guide stars.

(iii) Since Dye lasers are Tunable lasers, they are used to selectively excite molecules and study their reactions in research field.

(iv) Dye lasers are used to separate different isotopes of an element.

(v) Dye lasers are used to do cosmetic procedures like hair removal, skin rejuvenation and tattoo removal.

(vi) In medical field dye lasers plays a vital role in treating eye diseases and studying the effects of laser light on eye structures.