Nitrogen gas lasers

Photoexcitation was achieved by using a triggerable nitrogen gas laser (LGI-21). The laser output pulse was of duration 8ns at a wavelength of 337nm. 

A nitrogen gas laser pulse with a wavelength of 337 nm contains 3.83 mJ of energy. How many photons does it contain ... 

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The necessary pump powers can be achieved either by other lasers (e.g. nitrogen lasers, solid-state lasers or even focussed He-Ne- or Ar+-gas lasers) or by flash-lamps. The simplest practical arrangement is a square spectrophotometer cell, polished on all sides, containing the dye solution which is pumped by a nitrogen laser whose beam is focussed into a line parallel to and directly behind one of the cell windows. Then the Fresnel reflection from the two adjacent windows gives enough feedback in most cases, so that no additional resonator mirrors are needed and the dye laser oscillation starts. 

Figure 7.4—Light diffusion detector. Using nitrogen gas, the mobile phase is nebulised at the end of the column with a device of varying geometry. When a compound elutes from the column, the droplets under evaporation are transformed into fine particles that can diffuse light from a laser. This is called the Tyndall effect (it is similar to what is observed for a car when its lights are diffused by fog). The signal, detected by a photodiode, is proportional to the concentration of the compound. This detector can only be used for compounds that cannot be vaporised into the gas phase in the heated zone.

SYN NITROGEN CHLORIDE DOT CLASSIFICATION Forbidden SAFETY PROFILE Strong irritant by inhalation. An extremely unstable explosive. Reacts with liquid ammonia to form an explosive liquid. Explosive reaction with 1,3-butadiene, C2H6, C2H4, CH4, CsHs, phopshorus, silver azide, sodium. Reacts with water or steam to produce toxic and corrosive fumes of HCl. Has been used as an initiator in chemical gas lasers. When heated to decomposition it emits toxic fumes of Cr and NOx- See also CHLORINE and AZIDES. 

Another common laser class is that of gas lasers, which includes helium neon (HeNe) lasers, carbon dioxide (CO2) lasers, nitrogen lasers, and so on. The helium neon laser, widely used until the advent of the diode laser, was one of the first types developed and commercialized. As described above, it is a discharge-pumped gas laser, which generally produces an output measuring a few mW in power. 

The light source for time-resolved fluorescence can be a nanosecond pulse of Blum-line nitrogen laser, triple harmonics of yttrium-aluminum-garnet (YAG) laser, second harmonics of mode-locked dye, or gas laser. 

The most popular light sources in modern fluoremeters are gas lasers. At the present time, nitrogen, XeCl, XeF and KrF are used quite frequently for fluoremetry. The reason to use lasers as the light source for fluoremetry is the same as was given for Raman spectroscopy lasers emit monochromic light with very high intensity in comparison to the classical light sources. 

The nitrogen laser is pumped with a high-vollagc spark source that provides a momentary (1 to 5 ns) puLse of current through the gas. I he excitation creates a population inversion that decays very quickly by spontaneous emission because the lifetime of the excited stale is quite short relative to the lifetime of the lower level. The result is a short (a few nanoseconds) pulse of intense (up to I MW) radiaiion at. 337,1 nm. This output is used for exciting fluorescence in a variety of molecules and for pumping dye lasers. I he carbon dioxide gas laser is used to produce monochromatic Infrared radiation at 10.6 pm. 

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