RUBY LASER TOPICS TO BE DISCUSSED HISTORY CHARACTERSTICS

RUBY LASER

TOPICS TO BE DISCUSSED � HISTORY � CHARACTERSTICS � CONSTRUCTION � PRINCIPLE � SPIKING AND WORKING � THRESHOLD POWER � APPLICATIONS

HISTORY � The first laser to be operated successfully was the Ruby laser which was fabricated by Maiman in 1960.

CHARACTERSTICS � Ruby laser is a solid state laser. � Ruby crystals have high mechanical strength, high thermal conductivity. � Ruby laser is used where high powered pulsed output is required. � Ruby laser employs three level scheme of achieving population inversion. � Ruby laser employs optical pumping.

CONSTRUCTION • The Ruby laser consist of a single ruby crystal in the form of a cyclinderical rod of length about 5 cm and diameter 0. 5 cm. Its end surfaces are accurately plane and parrallel. • One of the ends is silvered with 100% reflectivity and the other end with 10% transmission. The two ends thus form a resonant cavity. • The Ruby rod is placed inside a Xenon flash lamp. • The flash lamp is connected to a capacitor which discharges a few thousand joules of energy in a few miliseconds. This results in power output of a few megawatt from Xenon lamp.

PRINCIPAL & WORKING 1) Ruby consists of aluminium oxide (Al 2 O 3) in which some of of the aluminium ions are replaced by chromium. For good lasing action, about 0. 05% of the atoms are that of chromium. Hence it is called pink ruby.

2) There are to main pump bands ( called the blue band & green band). 4 f 1 & 4 f 2 centered at 0. 42 μm & 0. 55μm respectively. These bands are about 1000Å wide each and they have a very small lifetime (≤ 10 -9 s) 3) Chromium ions gets excited to these levels by absorbing energy from xenon flash lamp (i. e. optical pumping). There is a fast non-radiative decay from these bands to 2 E-state, which is a metastable state and has a life time of 3*10 -3 s. The metastable level 2 E is split into two sub levels with a separation of ΔE=29 cm-1. 4)Thus , population inversion takes between 2Ā and Ē levels and the ground state 4 A 2 emitting a sharp doublet R 1( λ=6943Å) and R 2(λ=6928Å) lines.

SPIKING � The flash lamp emits bright flash of light of only a thousandth of a second duration. The moment the flash lamp stops operating the population of the upper level is depleted very fast and the laser action stops till the Xenon lamp flashes again. During a short period of time in which ruby is lasing , the emission is found to consist of spikes of high intensity as shown in fig. This phenomenon is termed as spiking of the laser.

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