Observation of upconversion fluorescence and stimulated emission based on three-photon absorption

The observations of three-photon-induced frequency-upconversion fluorescence and the highly directional stimulated visible emission in two dyes, 4-[p-(dicyanoethylamino) styryl]-N-methylpyridinium iodide (abbreviated as CEASP) and the complex of CEASP and Ce(NO₃) (abbreviated as CEASP-Ce), are reported. The photographs of the forward amplified spontaneous emissions spots, pumped by an optical parametric oscillator idler with a pulse width of 8 ns and a wavelength of 1.3 μ m, are shown. The upconversion fluorescence produced both in dimethyl formamide solution and 2-hydroxyethyl methacrylate (HEMA) polymer spans from green to red, with a cubic dependence on the pump light intensity. The experimental results imply that the existence of the lanthanide ion Ce^{3 +} sensitizes the nonlinear absorption and emission.     

Z-scan theory with simultaneous two- and three-photon absorption saturation

We report a theoretical investigation of the open-aperture Z-scan technique for an optically thin medium with simultaneous saturation of both two- and three-photon absorption. By using the Adomian decomposition method (ADM), we obtain the analytical expression for the normalized transmittance of the open-aperture Z-scan traces. Furthermore, the analytical results are good agreement with the numerical simulations. The results indicate that ADM is an effective yet quickly approach to evaluate the saturable properties originating from both two- and three-photon absorption.     

1.5-microm monolithic GaInNAs semiconductor saturable-absorber mode locking of an erbium fiber laser

We present a new monolithic GaAs-based semiconductor saturable absorber operating at 1.55 microm. An epitaxially grown absorber mirror in a GaInNAs/GaAs material system was successfully used to mode lock an erbium-doped fiber laser. The GaInNAs material system possesses intriguing physical properties and provides great potential for lasers and nonlinear optical devices operating at the 1.3-1.55-microm wavelength range.     

Polarization characteristics of stimulated emission of organic molecules when excited by intense XeCl laser radiation

We study the influence of the molecular structure, medium, and exciting-radiation parameters on the polarization, energy, and spectral characteristics of the emission of laser-active media based on the dicarboxylic derivative of p-terphenyl, rhodamine 101, and phenalemine 512. We found that the polarization of the stimulated emission of molecules when strongly excited under the conditions studied significantly depends on their structure, the pumping mode, the intensity and polarization of the exciting radiation, the shape and dimensions of the excited volume, and the phase state of the medium.     

The use of three-photon absorption for optical limiting of laser radiation

The results of a study of nonlinear refraction and nonlinear absorption at a wavelength of 532 nm in an LGO (Li₂Ge₂O₁₅) crystal by Z-scan methods are presented. It is shown that the nonlinear refraction is caused by self-focusing of the laser radiation, whereas the nonlinear absorption is three-photon in nature. The possibility of using an LGO crystal for producing the optical limiting of laser radiation of picosecond duration is demonstrated.     

Ultra-violet excited laser emission in Na2

Laser emission at different wavelengths in the range of 903–914 nm and around 2.5 m has been observed upon excitation of Na₂ by uv radiation from an excimer laser at 351 nm and an excimer pumped dye laser in this wavelength range. The emission is attributed to a cascade emission followed by . In addition, coupled with the laser emission around 910 nm, broad-band fluorescence peaking around 855.5 nm is observed which, eventually, may be the first observation of the bound-free transition in Na₂.     

超短激光脉冲调制上转换放大

在超短激光脉冲倍频过程中，由于调制不稳定性而产生多色圆锥辐射. 在多色圆锥辐射的任 意方向上同步注入一束宽带种子光，可以得到相应频率的调制上转换放大. 放大的光脉冲的 中心波长在500 nm时单脉冲能量最大可至150 μJ并且具有60 nm的频谱宽度. 通过改变种子 光的入射角度而实现上转换放大中心波长的连续调谐，范围约为290 nm. 关键词： 调制上转换放大 调制不稳定性 多色圆锥辐射     

同时辐射六种可见波长的CW-氦氖激光器的稳频及其输出的650nmCW氦氖受激Raman辐射

在中国计量科学研究院研制的612激光管上,利用反射率为99.95%宽带激光反射镜,得到同时辐射六种波长的连续振荡,其波长为:611.8,629.8,632.8,635.1,640.1和650um,测量了它们的物理参数,验证了650nm为氦氖Raman激光.对六种波长在简易装置上进行了稳频,各条激光谱线的频率稳定性优于10~(-10),利用锁模技术,各条激光谱线的频率稳定性可达10~(-12).     

Dynamics of stimulated emission and optical gain in highly excited superlattices

The results of low temperature (4.2K) stimulated emission and optical gain dynamics in highly photoexcited Al_xGa_1−xAs/As type I superlattices are presented. It was established that the increase of the pump quantum energy leads to the essential (more than one order) reduction of the stimulated emission intensity. The effect is explained in terms of quasiparticle system heating peculiarities in two-dimensional semiconductor structure.     

Investigations on coherence of stimulated Brillouin scattering excited by a single-mode-pulsed laser

We experimentally studied the temporal coherence of stimulated Brillouin scattering (SBS) excited by a single-longitude-mode laser. We found that the temporal coherence of SBS is variable but not fixed. In a certain range above the threshold pump energy in which the pulse of the Stokes component is Fourier limited, the coherence length is considerably long, although the temporal coherence decreases with increasing pulse compression rate. If the Fourier transform condition is not satisfied for the pulse of the Stokes component, the temporal coherence decreases rapidly, and the coherence length is much shorter.     

Low-frequency stimulated emission and induced absorption in a three-level atom

Investigations of the motion of conventional negative ions (electron bubbles) in He II under pressures above 11 bar have provided the only means of measuring the Landau critical velocity for roton creation,v _L, and for studying supercritical dissipation at higher velocities. Earlier work on roton creation is reviewed and it is pointed out that there is still no generally agreed explanation of the fact that the rotons seem to be emitted from the moving ionin pairs; nor is it known why the matrix element characterising the pair emission process should decrease rapidly with pressure. The possibility of studying these phenomena through use either of the fast ion (whose nature remains unknown), or of selected ions from the large variety of species that can be injected into He II by the recently developed technique of laser ablation, is discussed.     

Low-frequency stimulated emission and induced absorption in a three-level atom

We consider the excitation spectra of a bichromatically driven three-level atom in the lambda configuration and in the low-frequency domain. These dynamically induced spectra occur when the excitation fields operate at low intensities and are neither one- nor two-photon resonant with the various transitions of the system.     

Effects of excited-state absorption and stimulated emission in UV dyes on the shortening of laser pulses interacting with saturable absorbers

Saturation properties of the dyes in the presence of excited-state absorption and amplified spontaneous emission in the dye are studied theoretically. In the analysis the above two effects are included separately and it is shown that they are deleterious to the pulse-shortening capabilities of the dyes. It is also shown that in the conventional single-pass shortening of laser pulses with saturable dyes large pulse shortening ratios (20) may be expected if the dye saturation is combined with a properly delayed dye generation.     

Impact of doping on carrier recombination and stimulated emission in highly excited GaN:Mg

Light-induced transient grating and photoluminescence measurements were employed for carrier recombination studies in variously Mg doped GaN layers. Carrier lifetime and ambipolar diffusion coefficient were found to decrease with doping from 210 to 20 ps and from 2.0 to 0.9 cm²/s,respectively, which proved the degradation of electrical quality of the layers. A threshold of stimulated emission was found to depend non-monotonously on doping and had the lowest value of 0.19 mJ/cm² in the most doped layer. This dependence was explained in terms of degeneracy of the hole system.