Resonant pump cavities

Lasers have three primary components (Fig. 4) 1) an active medium that amplifies incident electromotive waves 2) an energy pump that selectively pumps energy into the active medium to populate selected levels and to achieve population inversion and 3) an optical resonator, or cavity, composed of two opposite mirrors a set distance apart that store part of induced emission concentrated in a few resonator modes. A population inversion must be produced in the laser medium, deviating from the Boltzman distribution thus, the induced emission rate exceeds the absorption rate, and an electromotive wave passing through the active medium is amplified rather than attenuated. The optical resonator causes selective feedback of radiation emitted from the excited species in the active medium. Above a pump threshold, feedback converts the laser ampler to an oscillator, resulting in emission in several modes. 

Lasers consist of a gain medium surrounded by a resonant optical cavity. The medium is pumped by an external energy source, usually by light from a flash lamp or from another laser or by an electric discharge. Laser emission occurs only when the number of particles in an excited state exceeds that in some lower energy state (population inversion, Figure 2.4) so that light amplification takes place in the cavity. 

The OPA should not be confiised with an optical parametric oscillator (OPO), a resonant-cavity parametric device that is syncln-onously pumped by a femtosecond, mode-locked oscillator. 14 fs pulses, tunable over much of the visible regime, have been obtained by Hache and co-workers [49, with a BBO OPO pumped by a self-mode-locked Ti-sapphire oscillator. 

The pump enhanced singly resonant OPO. It consists in an OPO in which the cavity is resonant for the signal and pump beams (Schiller et al., 1999). The basic properties of this device are the same as the SROPO s but with a lower threshold. 

The first stage was the production of a pulsed free-jet molecular beam of helium containing 20% CO, which was then crossed with an electron beam to produce ionisation. The ions were produced close enough to the beam nozzle for cooling to occur downstream. Some 4 cm from the nozzle the beam entered a confocal Fabry-Perot cavity where it was exposed to millimetre wave radiation close to 120 GHz in frequency. Following microwave excitation, when on resonance, the beam was probed with a Nd YAG pumped dye laser beam with the frequency chosen to drive rovibronic components of the A 2 U-X 2 + band system. Figure 11.54 shows two recordings of a spin component of the lowest rotational transition the line shown in (a) is... 

Optical pumped UV lasing spectrum of ZnO film was observed as shown in figure 5. The samples were optically pumped by a frequency-tripled mode-locked Nd YAG laser 355nm, lOHz repetition rate, 15ps pulse width. The pump beam was focused to a spot with diameter of about 20 pm on the surface of ZnO film. The threshold of lasing was as low as 0.24 pJ. From the lasing spectrum, we could find that much narrow lasing peak with line-width less than 0.6nm. This was due to self-formed resonator cavities [14]. 

Fig. 5. Experimental equipments for matrix isolation electron spin resonance (MIESR) spectroscopy (1) catalyst (2) gas inlet (3) thermocouple well (4) pressure probe (5) metal valve (6) O-ring joints (7) gate valve (8) butterfly valve (9) two vacuum pump (10) vacuum shroud (11) sapphire rod (12) microwave cavity and (13) quadrupole mass spectrometer inlet. Reprinted from Reference 45).

---