Tunable Laser

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TUNABLE LASER
by SIDDHARTHA
SOUMITRA
SNEHA CHAKRABORTY
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What is tunable laser?

• A laser in which the frequency of the emitted
  radiation can be changed across some range in the
  UV , visible and IR regions of the
  electromagnetic spectrum. A tunable laser
  consists of an optical gain medium ,a pumping
  process for stimulating and the frequency
  selective optical feedback

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Brief history and background

• Tunable lasers were discovered by Sorokin and
  Lankard in 1966. This was a Dye laser. Next a
  narrow-linewidth tunable laser was invented in
  1972.
• Multiple-Prism grating arrangements
• in several configurations are used in
• diode, dye, gas and other tunable lasers.
• Usually tunable lasers have very large bandwidth
  allowing tuning over a range of tens to hundreds
  of nanometres.
• .

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How does a tunable laser work?

• To create a tunable laser, the cavity coatings
  must be sufficiently broadband to accommodate the
  entire tuning range.
• Three tuning mechanisms are in general use
  Littrow prisms, diffraction gratings, and
  birefringent
• filters .
• Littrow prisms-
• Littrow prisms are used with gas
• lasers that operate at discrete
• wavelengths.
• Littrow is a 30-60-90-degree prism.
• The surface opposite the 60-degree
• angle coated with a broadband high-
• reflecting coating.

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• Diffraction gratings-
• Gratings are used for laser systems that require
  a higher degree of dispersion than that of a
  full-dispersing prism.
• Birefringent filters-
• The filter is made from a thin, crystalline-
• quartz plate.
• The filters are placed at Brewsters
• angle in the laser beam.
• Rotating the filter around the normal to its face
  shifts the transmission bands, tuning the laser.

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classification

• A tunable laser is a laser whose wavelength of
  operation can be altered in a controlled manner.
  There are many types and categories of tunable
  lasers. They exist in the gas, liquid, and solid
  state. Among the types of tunable lasers
  are excimer lasers, gas lasers (such
  as CO2 and He-Ne lasers), dye lasers (liquid and
  solid state), transition metal solid-state
  lasers, semiconductor crystal and diode lasers,
  and free electron lasers.

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• Excimer laser-An excimer laser (sometimes more
  correctly called an exciplex laser) is a form
  of ultraviolet laser which is commonly used in
  the production of microelectronic devices  eye
  surgery, psoriasis treatment and micromachining

• Gas laser-A gas laser is a laser in which
  an electric current is discharged through
  a gas to produce coherent light.The gas laser was
  the first continuous-light laser and the first
  laser to operate on the principle of converting
  electrical energy to a laser light output.

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• Dye laser-A dye laser is a laser which uses
  an organic dye as the lasing medium, usually as
  a liquid solution

• Solid state laser-A solid-state laser is
  a laser that uses a gain medium that is a solid.
  Generally, the active medium of a solid-state
  laser consists of a glass or crystalline "host"
  material to which is added a "dopant" such
  as neodymium, chromium, erbium, orytterbium .
  Titanium-doped sapphire is the most common
  tunable solid-state laser.

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Diode laser-A laser diode or LD is an
electrically pumped semiconductor laser in which
the active laser medium is formed by a p-n
junction of a semiconductor diode similar to that
found in a light-emitting diode

• Free electron laser-A free-electron laser (FEL),
  is a type of laser whose lasing medium consists
  of very-high-speed electrons moving freely
  through a magnetic structure.

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Tuning mechanism-

• Electric field-induce index change-
• An electrical field is applied that changes the
  refractive index of the waveguide.
• Thermally-induced index change-
• Heat is applied by a resistive method to the
  tuning section of the laser

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Types of tunability-

• Single line tuning-
• Tuning of the laser output across the narrow
  linewidth can be achieved by placing
  wavelength-selective optical elements into the
  laser's optical cavity  to provide selection of a
  particular longitudinal mode of the cavity.
• Multi line tuning-
•  If a dispersive element (e.g. prism) is
  introduced into the optical cavity, tilting of
  the cavity's mirrors can cause tuning of the
  laser.
• Multi line tuning allows tuning of the laser to a
  number of lines from the ultraviolet and blue thro
  ugh to green wavelengths.

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• Narrowband tuning-
• They can be continuously tuned over a significant
  wavelength range.
•  If the temperature of the laser is changed, the
  index change of the DBR structure causes a shift
  in its peak reflective wavelength and thus the
  wavelength of the laser.
• Widely tunable Laser-
• They have a much larger tunable range.
• By the use of vernier tunable Bragg mirrors and a
  phase section, a single mode output range of
  gt50nm can be selected

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How tunable lasers are used?

• Diagnose diseases in human body-With the use of
• Optical fibers, laser lights can
• travel through catheters into
• the human body to
• characterize and diagnose
• diseases.
• Tunable laser can detect changes in materials
  like buildings ,bridges and airplanes bodies or
  measure the depth of streams , rivers or
  reservoirs

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Industrial uses-precise time
standards are used everyday in high speed
communications systems, television transmissions,
financial transactions ,power distributions
,terrestrial and space navigation systems
including GPS. Tunable lasers allows the better
accuracy in measuring the natural resonance of
cesium , the definition of time.
Spectroscopy-they are the powerful tool for
reflection and transmission and spectroscopy .
spectroscopy enables themeasurement of even
trace amounts of a particular atom ormolecule
like oxygen ,carbon dioxide or water vapor.
E.Gmonitoring industrial smokestacks or vehicle
exhausts
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Solar cell-They can be used in the solar cells
in a light beam induced current.
Switching wavelengths-Tunable lasers are
used to switch wavelenghths into metro area
networks . Power consumption-Tunable
lasers can be used in less power consumption.
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Future applications

• In Computer Optics- Computer links and
  optical interconnects .
• Optical Sensing Optical fiber sensing and
  encoders .
• They can be Used in Bar code readers.
• In Multi Beam Search Lights.
• Displays Array light sources ,multi beam search
  lights.
• Optical cross connects-Used to switch
  wavelengths in metro area networks

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Economical Impact

• Today as opto electronics become more commercial,
• this market generates about 15 billion a year.
• The world for tunable lasers by 2016 should be
  about
• 2.8 billion a year.
• It is making money now-a-days.
• Future Market Projection- the world market for
  tunable lasers by 2007 should be about 2.4
  billion a year

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Acknowledgement
I would like to express my special thanks to To
our teacher as well as our friends and Parents
who helped me in doing this Presentation and
without whom this could not be possible.
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References

• www.wikipedia.com
• www.powershow.com
• www.powerpoint.com

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Thank u