Cavity length

For a cavity length of, for example, 50 cm the axial mode separation is 300 MFIz... 

Figure 9.40 shows the IgSg band of HCN involving one quantum of Vi, the CN stretching vibration, and six quanta of V3, the CH stretching vibration. This extremely weak band was observed using a cavity length of 1.3 m. 

Lasing occurs whenever the gain arising from stimulated emission exceeds the cavity losses. Internal losses, a, result from absorption and scattering of light. The reflectivity, R, of the mirror facet must be <1 and this contributes a loss term of (1/L)ln(l/E), where Eis the cavity length. At threshold, the gain, is equal to losses and... 

The two-dimensional carrier confinement in the wells formed by the conduction and valence band discontinuities changes many basic semiconductor parameters. The parameter important in the laser is the density of states in the conduction and valence bands. The density of states is gready reduced in quantum well lasers (11,12). This makes it easier to achieve population inversion and thus results in a corresponding reduction in the threshold carrier density. Indeed, quantum well lasers are characterized by threshold current densities as low as 100-150 A/cm, dramatically lower than for conventional lasers. In the quantum well lasers, carriers are confined to the wells which occupy only a small fraction of the active layer volume. The internal loss owing to absorption induced by the high carrier density is very low, as Httie as 2 cm . The output efficiency of such lasers shows almost no dependence on the cavity length, a feature usehil in the preparation of high power lasers. 

The cavity length, x measured from the lee side of the building, is estimated by the following (Hosker, 1984) ... 

Equation (7.1) states that the intensity of the interference signal is a periodic function of the cavity length, the refractive index, and the wavelength. For most chemical sensing applications, the interference signal needs to be processed to obtain either the absolute value or the relative change of the refractive index that... 

The temperature dependence of the fabricated open cavity FP device was evaluated experimentally. The sensor was placed in a programmable electric tubular furnace. The temperature of the furnace was increased from room temperature to 1,100°C at a step of 50°C. The cavity length as a function of the temperature is plotted in Fig. 7.11, where it increased nearly linearly following the increase of temperature. The temperature sensitivity of the particular FP device under test was estimated to be 0.074 nm °C 1 based on the linear fit of the measurement data. The equivalent coefficient of thermal expansion (CTE) of the fiber FP device was 2.4x10 6oC. ... 

Figure 12.17. (a) Diode laser band structure. (1) In thermal equilibrium. (2) Under forward bias and high carrier injection. Ec, v, and f are the conduction band, valence band, and Fermi energies respectively, (b) Fabry-Perot cavity configuration fora GaAs diode laser. Typical cavity length is 300//m and width 10/tm. d is the depletion layer. 

Usually, mainly Doppler broadening determines the gain profile of a particular laser transition. Indeed, due to the different configurations achievable with gas lasers (namely, a large cavity length), the laser line can be narrower than the Doppler linewidth. Different experimental realizations of single-mode lasers are detailed elsewhere (Demtroder, 2(X)3). 

EXAMPLE 2.4 Obtain the separation between adjacent modes in a He Ne laser whose cavity length is 1 m. The emission wavelength is X = 632.8 nm. 

The frequency of a single-mode laser inside the spectral gain profile of its active medium is mainly determined by the eigenfrequency of the active laser cavity mode. Therefore any instability of resonator parameters, such as variation of cavity length, mirror vibrations or thermal drifts of the refractive index will show up as frequency fluctuations and drifts of the laser line. 

To excite a supersonic jet using cavity acoustics, an acoustically open cavity was placed along the direction of the jet at the nozzle exit close to the shear layer. An acoustically open cavity is characterized by a cavity length-to-depth... 

Enhancement of the Hght-matter interaction in a microscopic optical cavity is achieved because Hght trapped in the cavity has longer effective interaction time with absorbers. For short laser pulses, cavity length exceeding CTp allows avoidance of the interference between the pulses incident and reflected from the mirrors. Spectral selectivity of planar Fabry-Perot cavities can be used to achieve the localization at the resonant wavelength of the cavity. 

The CO2 lasers were also investigated in connection with chaotic behavior, and here we mention the most important papers in the field. The chaotic behavior associated with a transverse mode structure in a cw CO2 laser was observed in 1985 [40]. In the CO2 laser with elastooptically modulated cavity length, a period doubling route to chaos was also found [41]. 

---