Nonsaturable Absorption Research Articles

Parametric studies of an electron-beam-pumped krypton-rich KrF laser

This paper describes the results of a detailed experimental study of an electron-beam-pumped, high Kr concentration KrF laser. The excitation rate is 1.4 MW/cm3 for 1 atm of Kr gas. The formation efficiency of KrF* and extraction efficiency are estimated using calculated values of saturation intensity and g0/α0, the ratio of small-signal gain to saturable absorption, together with measured values of g0 and the ratio of g0 to nonsaturable absorption (αn). Although the highest formation efficiency of 24% is observed at 99.7% Kr concentration, the effect of finite vibrational-relaxation rate significantly decreases the KrF* density accessible to lasing at high Kr concentration due to the shorter lifetime of KrF*. KrF* vibrational-relaxation rates of 4×10−11 and 5×10−11 cm3 s−1 are determined for Ar gas and Kr gas, respectively. A decrease of g0/α0 and g0/αn resulting in low extraction efficiency is observed at high Kr concentration due to the relatively high α0 and αn. The intrinsic efficiencies are 11, 11.8, and 9% for 1 atm mixtures at 10, 50, and 99.7% Kr, respectively.

Double-pass versus expanding-beam concept for very large excimer laser amplifiers

In this communication, the scalability of large excimer laser amplifiers with nonsaturable absorption is examined in terms of two extraction geometries. These geometries include a single-pass expanding-beam concept, recently proposed as a means to extend the laser length beyond an absorption length product of unity, and a conventional double-pass rectilinear (nonexpanding) arrangement. It is shown that the double-pass configuration provides the same total-energy output with greater efficiency than the expanding-beam concept (assuming a constant expansion angle), but has an overall length that is smaller by a factor of ∼3.

Calcium Absorption during Development

During the period of natural weaning in the rat (beginning during the third week) the mechanisms of calcium absorption from the duodenum change from an efficient nonsaturable process, which is insensitive to vitamin D, to a combination of a less efficient nonsaturable process and a saturable vitamin D-dependent component. The stimulatory effect of vitamin D on active calcium transport requires the development of mucosal receptors for 1,25-(OH)2D3 and increasing circulating levels of 1,25-(OH)2D3. Concurrent increases in the concentration of the cytosolic calcium-binding protein (CaBP) support the suggestion that the CaBP mediates, in part, the effect of 1,25-(OH)2D3 on active calcium transport. The decline in the efficiency of nonsaturable calcium absorption during the third week coincides with, but is probably not due to, the loss of pinocytotic capacity of the small intestine. The time of appearance of the receptors for 1,25-(OH)2D3 and the decline in nonsaturable calcium absorption are under glucocorticoid control as are several other maturational events in the intestine at this time.

Calcium Absorption during Development

SummaryDuring the period of natural weaning in the rat (beginning during the third week) the mechanisms of calcium absorption from the duodenum change from an efficient nonsaturable process, which is insensitive to vitamin D, to a combination of a less efficient nonsaturable process and a saturable vitamin D‐dependent component. The stimulatory effect of vitamin D on active calcium transport requires the development of mucosal receptors for 1,25‐(OH)2D3 and increasing circulating levels of 1,25‐(OH)2D3. Concurrent increases in the concentration ##of the cytosolic calcium‐binding protein (CaBP) support the suggestion that the CaBP mediates, in part, the effect of 1,25‐(OH)2D3 on active calcium transport. The decline in the efficiency of nonsaturable calcium absorption during the third week coincides with, but is probably not due to, the loss of pinocytotic capacity of the small intestine. The time of appearance of the receptors for 1,25‐(OH)2D3 and the decline in nonsaturable calcium absorption are under glucocorticoid control as are several other maturational events in the intestine at this time.

ASE effects in small aspect ratio laser oscillators and amplifiers with nonsaturable absorption

A three-dimensional calculation of amplified spontaneous emission (ASE) is presented that allows rapid determination (with suitable approximation techniques) of extraction efficiency and power gain for small aspect ratio (length/width) laser amplifiers and oscillators. These calculations include nonsaturable absorption, ASE line-narrowing effects, and end mirrors that reflect ASE flux back into the active gain medium. The applicability of this technique has been verified for laser aspect ratios below unity, and results are presented that show the optimum scaling of extraction efficiency and power gain for large fusion class lasers. The technique is particularly suited to first-order design efforts where fast turnaround results are required. Nevertheless, the approach shows an accuracy of at least 10 percent when the laser medium is efficiently loaded with coherent flux.

Expanding beam concept for building very large excimer laser amplifiers

Optical extraction efficiency from conventional lasers and amplifiers with nonsaturable intrinsic absorption is substantially below the maximum efficiency at absorption length products exceeding unity. This result is caused by the fact that high intensities in the amplifier cause saturation of gain but not absorption. In this letter, a new scalable amplifier concept is analyzed which maintains near maximum extraction efficiency as the laser length increases beyond absorption length products of unity.

Method for determination of co-spectral gain and absorption coefficients in high-power lasers

A new method is described for determining the small-signal gain and non-saturable absorption coefficients over the same spectral region for high-power lasers. Preliminary tests of this method on the discharge-pumped XeCl excimer laser have yielded B 2σ→ X 2σ gain coefficients which are comparable to those observed in other experiments under similar excitation conditions. However, the absorption coefficient is found to be a high and nearly constant fraction (~ 1 4 ) of the gain. This result suggests that all of the absorption processes are due to excited species, including XeCl B 2σ.

Narrow-linewidth gain and saturation measurements of a KrF discharge laser

The gain and output characteristic of a KrF discharge laser module have been studied using a 0.1-cm−1 linewidth probe pulse generated from an etalon-narrowed injection-locked oscillator-amplifier system. A small signal gain coefficient of 0.115 cm−1 was measured. Saturation of the output intensity could be accurately modelled by assuming steady state conditions including a nonsaturable absorption of 0.01 cm−1 which yields a saturation intensity of 1.7 MW/cm2.

Bidirectional amplification with nonsaturable absorption and amplified spontaneous emission

A theory of bidirectional amplification is developed and applied to single-pass and double-pass laser amplifier configurations. The effects of nonsaturable absorption, longitudinal amplified spontaneous emission (ASE) gain saturation, and ASE line narrowing are included in a self-consistent formulation. An estimate of aperture scaling limitations due to transverse ASE is included. Laser performance is discussed for some conditions typical of large aperture, multikilojoule, rare gas halide (RGH) fusion amplifiers. This formulation permits tradeoff studies to be performed rapidly by altering variables spanning an eight-parameter space.

Oscillator performance and energy extraction from a KrF laser pumped by a high-intensity relativistic electron beam

A laser cell with 21 of excitation volume was used to study the electron-beam pumped KrF laser system at excitation rates of 1.8- 7.0 MW/cm3. The system was optimized as an oscillator for various mixtures of Ar, Kr, and F 2 at total pressures of 1000 and 2500 torr. The resulting optimum conditions gave an intrinsic efficiency (laser energy out/electron-beam energy deposited) of 12 percent for the 1000 torr total pressure mixture with an output energy of 11 J/1. An efficiency of 10 percent with an output of 40 J/1 was obtained for the 2500 torr mixture. The system was then used as an amplifier to measure the extracted power as a function of input power for the two mixtures. The small-signal gain go, the nonsaturable absorption α, and the saturation intensity I s were determined for the two mixtures. Analysis of the data gave g 0 = 16-18 percent/cm, \alpha = 0.75-1.25 percent/cm, and I s = 2 MW/cm2for the 1000 torr mixture and g 0 = 17-19 percent/cm, \alpha = 1.0-1.5 percent/cm, and I_{s} = 9 MW/cm2for the 2500 torr mix.

Flow dependence of nonelectrolyte absorption in the nephron

The axial flow dependence of nonelectrolyte absorption was examined in terms of a model incorporating interactions between net volume absorption and both saturable and nonsaturable solute absorption. The model solutions demonstrated that changes in transepithelial solute transport are produced by changes in the average luminal solute concentration. Even passive non-saturable solute absorption was shown to exhibit dependence on the perfusion rate, and, therefore, on the solute delivery rate, which could be incorrectly interpreted as demonstrating the presence of a saturable absorptive mechanism. For a unidirectional lumen-to-bath solute flux mediated in part by a saturable mechanism, the observed flux is dependent on the permeability of any parallel nonsaturable permeation pathway. This permeability also sets a lower bound on the luminal solute concentration which may be achieved during active net solute absorption by determining the rate of passive solute backleak. Extension of the model to incorporate dependence of net volume absorption on the delivery of nonelectrolytes predicted a relationship between perfusion rate and net volume absorption equivalent to approximately one-third of complete glomerulotubular balance.