Absence Of Saturation Effects Research Articles

Synthesis and thermoluminescence behavior of novel Sm3+ doped YCa4O(BO3)3 under beta irradiation

This study investigates the luminescent properties and dosimetric potential of YCa4O(BO3)3:0.5%Sm3+ phosphor synthesized via the combustion method. Dose-response investigations unveil a noteworthy linear increment in thermoluminescence (TL) intensity, emphasizing a remarkable linearity spanning a broad dose range from 0.1 to 300 Gy. Unusual heating rate effects are explored, revealing a shift in TL glow curve peak temperature (i.e 200 °C) towards higher temperatures with increasing heating rate. Speculative models, including Kinetic Trapping Effect, Thermal Quenching Compensation, and Defect Activation Energy Changes, are proposed. The study employs the Tmax-Tstop method to identify characterize glow curve peaks, and the Initial Rise method for the low-temperature segment analysis, revealing seven distinct trap levels at various depths within the bandgap. Glow curve deconvolution using the Complex Glow Curve Deconvolution (CGCD) method delineates a multi-peak structure, offering valuable insights into luminescent mechanisms. The model exhibits a Figure of Merit (FOM) of 1.71%, within an acceptable range, affirming its reliability. However, interpretation of the activation energy and frequency factor values suggests intricate site processes, necessitating a nuanced analysis to understand the material's luminescent characteristics. The YCa4O(BO3)3:0.5%Sm3+ phosphor demonstrates promising characteristics for precise dosimetry, with linear dose response, absence of saturation effects, and intriguing heating rate behavior.

Cavity-enhanced harmonic generation in silicon rich nitride photonic crystal microresonators

We report second and third harmonic generation in photonic crystal cavities fabricated in a suspended silicon-rich nitride membrane under resonant continuous-wave excitation at telecom wavelength. Two-dimensional photonic crystal cavities with a far-field optimized line-width modulated design were employed. A quality factor at fundamental wavelength as high as Q = 1.3 × 104 and a coupling efficiency ηc ≈ 30% enabled us to exploit the cavity field enhancement to achieve the generation efficiencies ρSH = (4.7 ± 0.2) × 10−7 W−1 and ρTH = (5.9 ± 0.3) × 10−5 W−2. The absence of saturation effects at high power and the transparency of the device at the second harmonic wavelength suggest the absence of two-photon absorption and related detrimental effects.

Metastable helium in absorption towards ζ Ophiuchi★

We report on the detection of a metastable He i* absorption line at 3889 A in a spectrum of ζ Ophiuchi from the Ultraviolet and Visual Echelle Spectrograph with an extremely high signal-to-noise ratio (∼3500), which was collected using the 8-m telescope UT2 at Paranal. We cannot conclusively determine whether the He i* absorption arises within the H ii region or within the foreground H i clouds, which are responsible for interstellar CH, CH+, Na i, Ca ii, K i, etc., absorption, because the radial velocities of the main mass of gas are nearly identical in both regions. The measured equivalent width (1.0 ± 0.07 mA) of the line gives a column density of 1.158(± 0.081) × 1011 cm−2, when we assume the absence of saturation effects, and an oscillator strength of f= 0.0645. We estimate the ionization rate of helium to be 1.491 × 10−13, if the helium relative abundance in the H i cloud (with respect to hydrogen) is solar, and 7.475 × 10−14 cm−2, if the helium abundance is enhanced by the nearby star.

Radiometry and laser safety standards.

The application of occupational limits (ELs) in the outdoor laser environment requires an understanding of the radiometric methods required to evaluate field exposures with respect to the ELs. The limiting aperture required to adequately specify the EL must always be kept in mind. Since all exposure limits are defined as a function of time, electro-optical detectors and instrumentation must have an adequate temporal response and have an absence of saturation effects. As a field-expedient method thermally sensitive paper can also be employed to estimate the output radiant exposure of pulsed lasers. For evaluating potential ocular hazards in the retinal hazard spectral region (400 to 1400 nm), one should employ a 7-mm aperture. For evaluating potential hazards to the skin and the cornea, a 1-mm limiting aperture is justified. Although the impact of the 1-mm limiting aperture is to reduce the limiting power which is considered safe--the accessible emission limit for Class 1 laser products, it nevertheless is justified for field exposure of the eye, as has been shown in recent experimental studies of corneal injury.

Nondegenerate reversal of polarized light by four-wave interaction in a resonant medium

The representation of irreducible tensor operators is used to develop a theory of wavefront reversal (WFR) in the absence of saturation effects. This theory deals with arbitrarily polarized waves in a two-level resonant medium having arbitrary angular momenta. It is shown that there are three different physical reversal mechanisms associated with a nonuniform population and with the coherence of the magnetic sublevels in the field. An investigation is made of the influence of the decay times of the polarization moments of the system (the total population, orientation, alignment) on WFR. In particular, it is shown that, subject to specific relationships between the decay times, new collision-induced reversal processes can occur in the presence of deorienting collisions. An investigation is made of the spectral composition of the reflection coefficient of the reversed wave and it is shown that there are various spectral ranges of efficient reversal which in general depend on the polarizations of the interacting waves.

Trap-controlled dispersive transport and exponential band tails in amorphous silicon

The theory of trap-controlled dispersive transport based on exponential band-tail traps is extended to include the saturation of trap occupancy at high excitation levels. The absence of saturation effects in the transient photocurrent experiment of Hvam and Brodsky is shown to contradict the band-tail hypothesis of this model.

The records of solar wind and solar flares in aubrites

A large number of individual enstatite crystals of the gas-rich aubrites Khor Temiki, Staroe Pesyanoe and Bustee was analyzed for implanted helium and for steep gradient ion tracks in order to investigate the relation between solar flare irradiation and solar wind implantation with extreme local resolution. Irradiated and non-irradiated crystals coexist within the gas-rich phases of the aubrites investigated. Statistically in a given meteorite the proportion of crystals with implanted solar wind is similar to the proportion of solar flare irradiated crystals. It varies from aubrite to aubrite in the sequence of their bulk contents of trapped rare gases. For nine enstatites, tracks and rare gases were subsequently measured within the same crystal. The results support the intimate association of solar flare tracks and implanted He. The 4He-surface concentrations of irradiated crystals vary between <5 × 10 −7 and 10 −4 cm 3 STP/cm 2. The absence of saturation effects together with the low degree of elemental gas fractionation indicates very short solar wind exposure times (< 100 yr) rather than strong diffusion losses. The evidence from tracks and rare gases can be understood in terms of an early simultaneous irradiation of aubritic crystals by solar wind and solar flare particles on top of a regolith-covered parent body.

Specific luminescence studies in plastic scintillators

Using a thin-film scintillator detector direct measurements of relative specific luminescence ($\frac{\ensuremath{\Delta}L }{ \ensuremath{\Delta}x}$) and luminescence efficiency ($\frac{\ensuremath{\Delta}L }{ \ensuremath{\Delta}E}$) values have been obtained for an organic scintillator exposed to transiting light and heavy ions. These experimentally obtained luminescence data are presented as a function of ion energy, velocity, and stopping power for a wide variety of transiting ions ($Z=1,2,8,17,18,35,53$). The data emphasize the luminescence response in the low-energy range corresponding to maximum ion stopping power. Common trends, unique characteristics, and other interesting features pertinent to these graphical plots are noted and discussed. The double-valuedness of the specific luminescence $\frac{\ensuremath{\Delta}L }{ \ensuremath{\Delta}x}$ when plotted as a function of specific energy loss $\frac{\ensuremath{\Delta}E }{ \ensuremath{\Delta}x}$ is interpreted as arising mainly from the decreased effective charge of the ion as it picks up electrons in the slowing-down process. It is further emphasized that the specific energy-loss per se is an inappropriate parameter for characterizing (in a direct way) the luminescence response. A new model is formulated based on a conceptually different approach to the problem of luminescence production along and about the path of a transiting energetic ion. In essence, the number of electrons scattered into a thin disk of scintillator material (perpendicular to the ion trajectory) is taken, in the absence of saturation effects, as proportional to the luminescence response from that disk. Saturation effects are included by deriving an explicit relation for the number of electrons scattered per unit area of disk at a distance $r$ from the ion path. Above a critical number per unit area, no additional luminescence response is generated. These number-density profiles are plotted for various ions of different energies. Finally, a plot of the calculated specific luminescence for various heavy ions is shown to be in remarkably good agreement with experimental data.

Efficiency of high-order optical harmonic generation and of many-quantum processes in a multimode radiation field

An analysis is made of the generation of harmonics and of many-quantum processes (more than three quanta) in a specified field of laser radiation. Different statistics of the mode phases are considered and the absence of saturation effects is assumed. General relationships are derived for the calculation of the efficiency ηk of a nonlinear k-th order process in the case of arbitrary numbers of locked and nonlocked modes. It is shown that mode locking increases considerably the value of ηk. Precise values of ηk are found for third- and fourth-order processes in the case of mode locking and up to sixth order in the absence of such locking.

The sensitivity of electron paramagnetic resonance spectrometers using parametric and maser preamplifiers

The improvement in the sensitivity of electron paramagnetic resonance spectrometers obtained when a parametric or maser preamplifier is inserted between the sample cavity and the detection system is examined. It is shown that the addition of such a preamplifier is justified only when the paramagnetic sample saturates at power levels of 0 (1) μW and the spectral purity of the microwave power oscillator is less than 1: 106. It is concluded that the additional complexity of the system is seldom justified since the improvement in sensitivity cannot exceed a factor of 101/2 when the microwave diodes are operated with minimum noise figure. The same improvement in sensitivity can be achieved in the absence of saturation effects by increasing the oscillator power level by a factor of ten since the sensitivity is proportional to the square root of the sample cavity power.