ABSTRACT
We have developed a simple approach to deriving the efficiency of Q-switched four-level lasers, valid even for arbitrarily long lower laser level lifetimes. By eliminating time dependence from the calculation, numerical solutions can be obtained very rapidly. Its threshold and limiting slope efficiency values provide useful estimates for free-running pulsed four-level lasers as well as Q-switched.
ABSTRACT
Evidence is presented that a "three-for-one" process based on two cross-relaxations between Pr3+ ions efficiently populates the mid-infrared-emitting 3H5 manifold in a Pr3+-doped low-maximum-phonon-energy host. The concentration dependence of infrared fluorescence spectra and lifetimes of polycrystalline Pr:KPb2Cl5 initially excited to the 3F3,4 manifolds indicate that the 3500-5500-nm fluorescence becomes strongly favored over shorter-wavelength infrared emission bands in the higher-concentration sample. The strong concentration dependence of the 3F3 and 3H6 manifold lifetimes suggests that both of these decay by cross-relaxation processes, resulting in more than one ion excited to 3H5 for each ion initially excited to 3F3. Indeed, modeling and accounting for all possible decay paths indicate that, on average, about 2.3 ions are excited to 3H5 for each initially-excited ion. This confirms that the three-for-one excitation process must occur and contribute significantly to the total excitation efficiency. These results indicate that the two distinct cross-relaxation processes observed between Pr ions result in substantially higher excitation quantum efficiency, 230%, than any ever reported in rare-earth doped materials.
ABSTRACT
Mid infrared time-resolved emission spectra were recorded from laser-induced carbon plasma. These spectra constitute the first study of carbon materials LIB spectroscopy in the mid infrared range. The carbon plasma was induced using a Q-switched Nd: YAG laser. The laser beam was focused to high purity graphite pellets mounted on a translation stage. Mid infrared emission from the plasma in an atmospheric pressure background gas was detected by a cooled HgCdTe detector in the range 4.4-11.6µm, using long-pass filters. LIB spectra were taken in argon, helium and also in air. Despite a gate delay of 10µs was used there were strong backgrounds in the spectra. Superimposed on this background broad and noisy emission bands were observed, the form and position of which depended somewhat on the ambient gas. The spectra were digitally smoothed and background corrected. In argon, for instance, strong bands were observed around 4.8, 6.0 and 7.5µm. Using atomic spectral data by NIST it could be concluded that carbon, argon, helium and nitrogen lines from neutral and ionized atoms are very weak in this spectral region. The width of the infrared bands supports molecular origin. The infrared emission bands were thus compared to vibrational features of carbon molecules (excluding C2) of various sizes on the basis of previous carbon cluster infrared absorption and emission spectroscopic analyses in the literature and quantum chemical calculations. Some general considerations are given about the present results.
