page_title: Nitrogen laser
section_title: Electrodynamics
hierarchical_section_title: Nitrogen laser / Electrical / Electrodynamics
caption_attribution_description: Nitrogen Laser. Composed from various sources on the Web and in the Journal on Scientific Instruments, by me using my computer. Nothing was electronically copied. Everthing was altered. 2005-08.
context_page_description: A nitrogen laser is a gas laser operating in the ultraviolet range using molecular nitrogen as its gain medium, pumped by an electrical discharge.
  The wall-plug efficiency of the nitrogen laser is low, typically 0.1% or less, though nitrogen lasers with efficiency of up to 3% have been reported in the literature. The wall-plug efficiency is the product of the following three efficiencies:
  electrical: TEA laser
  gain medium: This is the same for all nitrogen lasers and thus has to be at least 3%
  inversion by electron impact is 10 to 1 due to Franck–Condon principle
  energy lost in the lower laser level: 40%
  optical: More induced emission than spontaneous emission
context_section_description: The electronics is a circuit composed of a spark gap, a capacitor, and the discharge through the nitrogen. First the spark gap and the capacitor are charged. The spark gap then discharges itself and voltage is applied to the nitrogen.
  An alternative construction uses two capacitors connected as a Blumlein generator. Two capacitors are connected so that one plate is a common earth, the others are each connected to the spark gap electrodes. These capacitors are often constructed from a single layer of printed circuit board, or similar stack of copper foil and thin dielectric. The capacitors are linked through an inductor, a simple air-spaced coil. One capacitor also has a small spark gap across it. When HT is applied, the two capacitors are charged slowly, effectively linked by the inductor. When the spark gap reaches its triggering voltage, it discharges and quickly reduces that capacitor's voltage to zero. As the discharge is rapid, the inductor acts as an open circuit and so the voltage difference across the transverse spark gap (between the two capacitors) rises rapidly until the main spark gap discharges, firing the laser.
  The speed of either circuit is increased in two steps.
  First, the inductance of all components is reduced by shortening and widening conductors and by squeezing the circuit into a flat rectangle. The total inductance is the sum of the components:
  The intense discharge is reported to distort oscilloscopes nearby. 
  This can be reduced by building the laser symmetrically into a grounded cylinder with the spark gap at the bottom, the laser at the top,
  capacitor 1 left and right, and capacitor 2 left and right stacked onto capacitor 1.
  This has the further advantage of reducing the inductance.
  And this has the disadvantage that the laser channel cannot be inspected for sparks anymore.
  Secondly, transmission line theory and waveguide theory is applied to achieve a traveling wave excitation.
  Measured nitrogen laser pulses are so long that the second step is unimportant.
  From this analysis it follows that:
  the end mirror and the spark gap are on the same side
  a long narrow laser at atmospheric pressures is ineffective
caption: Low inductance implementation top view. Erratum: Caps should be slightly longer than the channel and have rounded corners.
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