Docsity
Docsity

Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity


Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan


Guidelines and tips
Guidelines and tips

Advanced Ruby laser notes, Lecture notes of Physics

Give a detailed analysis of ruby laser

Typology: Lecture notes

2018/2019

Uploaded on 04/04/2019

vedant-shah
vedant-shah 🇮🇳

3

(2)

2 documents

1 / 5

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
Laser
Ruby Laser
The ruby laser is the first type of laser actually constructed, first demonstrated in 1960 by T. H.
Maiman. The ruby mineral (corundum) is aluminum oxide (Al2O3 ) with a small amount (about
0.05%) of chromium ions (Cr3+) which gives it its characteristic pink or red color by absorbing
green and blue light.
The ruby laser is used as a pulsed laser, producing red light at 6943Å. After receiving a pumping
flash from the flash tube, the laser light emerges for as long as the excited atoms persist in the
ruby rod, which is typically about a millisecond.
The ruby laser has following main parts:
1. The working substance (active medium)- is in the form of a rod of ruby crystal (10 cm in
length, 0.8 cm in diameter) in which Cr3+ are active centers while Al and O2 are inert.
2. The resonance cavity- is made by silvering and polishing the ends of ruby rod. Fully reflecting
plates at the left and a partially reflecting plate at the right, both optically plane and accurately
parallel.
3. The optical pumping system -consists of a helical xenon discharge tube. It produces flash of
few milliseconds.
Ruby laser uses a three level pumping scheme. The xenon discharge generates a flash of white
light for few milliseconds. The Cr+3 ions are excited to the E3 level by absorbing green and blue
component of white light. From there the Cr+3 ions undergo non-radiative transitions and
quickly drop to the metastable level E2. The metastable state has greater life time than E3.
Therefore Cr+3 ions accumulate at E2. When more than half ions are accumulated at E2 the
population inversion is established between E2 and E1. A chance spontaneous emission leads to
chain stimulated emission. Red light (of wavelength 6943 Å) emerges from the front face.
pf3
pf4
pf5

Partial preview of the text

Download Advanced Ruby laser notes and more Lecture notes Physics in PDF only on Docsity!

Laser

Ruby Laser

The ruby laser is the first type of laser actually constructed, first demonstrated in 1960 by T. H. Maiman. The ruby mineral (corundum) is aluminum oxide (Al 2 O 3 ) with a small amount (about 0.05%) of chromium ions (Cr3+) which gives it its characteristic pink or red color by absorbing green and blue light. The ruby laser is used as a pulsed laser, producing red light at 6943Å. After receiving a pumping flash from the flash tube, the laser light emerges for as long as the excited atoms persist in the ruby rod, which is typically about a millisecond. The ruby laser has following main parts:

  1. The working substance (active medium)- is in the form of a rod of ruby crystal (10 cm in length, 0.8 cm in diameter) in which Cr3+ are active centers while Al and O2 are inert.
  2. The resonance cavity- is made by silvering and polishing the ends of ruby rod. Fully reflecting plates at the left and a partially reflecting plate at the right, both optically plane and accurately parallel.
  3. The optical pumping system - consists of a helical xenon discharge tube. It produces flash of few milliseconds. Ruby laser uses a three level pumping scheme. The xenon discharge generates a flash of white light for few milliseconds. The Cr+3 ions are excited to the E3 level by absorbing green and blue component of white light. From there the Cr+3 ions undergo non-radiative transitions and quickly drop to the metastable level E2. The metastable state has greater life time than E3. Therefore Cr+3 ions accumulate at E2. When more than half ions are accumulated at E2 the population inversion is established between E2 and E1. A chance spontaneous emission leads to chain stimulated emission. Red light (of wavelength 6943 Å) emerges from the front face.

Semi-Conductor Laser

PN-junction Laser: A semiconductor laser is a specially fabricated pn junction device (both the p and n regions are highly doped) which emits coherent light when it is forward biased. It is made from Gallium Arsenide (GaAs) which operated at low temperature and emits light in near IR region.Now the semiconductor laser are also made to emit light almost in the spectrum from UV to IR using different semiconductor materials. They are of very small size (0.1 mm long), efficient, portable and operate at low power. These are widely used in Optical fibre communications, in CD players, CD-ROM Drives, optical reading, laser printing etc. p and n regions are made from same semiconductor material (GaAs). A p type region is formed on the n type by doping zinc atoms. The diode chip is about 500 mm long and 100mm wide and thick. the top and bottom faces has metal contacts to pass the current. the front and rare faces are polished to constitute the resonator (fig 1).

He – Ne laser

The most common and inexpensive gas laser, the helium-neon laser is usually constructed to operate in the red at 6328 Å. It can also be constructed to produce laser action in the green at 5435 Å and in the infrared at 15,230 Å. The He – Ne laser has following main parts:

  1. The working substance (active medium)- is a long gas discharge tube filled with Helium and Neon gases in ratio 10:1. Ne atoms are active centers where He atoms helps Ne in achieving population inversion.
  2. The resonance cavity- the two mirrors arranged externally one is fully reflective and other is partially transmissive forms the optical resonator.
  3. Pumping scheme- atoms are excited by electrical discharge. The He atom is pumped to excited state by electrical discharge. One of the excited levels of helium at 20.61 eV is very close to a level in neon at 20.66 eV, so close in fact that upon collision of helium and a neon atom, the energy can be transferred from the helium to the neon atom during collision. Thus the population inversion is achieved between E4 and E3 of Neon atom.