Competition between four-wave mixing and amplified spontaneous emission

There has recently been considerable interest in nonlinear optical interactions in which two different processes compete with one another. In this paper, we review some recent work in this area, and describe the results of our own investigation of competition between four-wave mixing and amplified spontaneous emission. We find that under two-photon excitation of the sodium 3d level, new optical frequency components can be generated either by amplified spontaneous emission at the 3d→3p transition frequency or by a resonantly enhanced four-wave mixing process. We have observed competition between these two processes, resulting in the suppression of amplified spontaneous emission. The transfer of population to the 3d level is inhibited by the destructive interference between two different pathways connecting the ground and upper levels.     

Suppression of amplified spontaneous emission in a femtosecond chirped-pulse amplifier

The suppression of amplified spontaneous emission (ASE) that arises during the femtosecond chirped-pulse amplification is presented. On the basis of the distinct differences in the spatial, temporal and spectral region between ASE and the amplified laser signal, the noise arising from ASE was effectively filtered out. The ratio between the amplified femtosecond pulse and the ASE peak power was higher than 10⁷. Pulses as short as 38 fs were amplified to peak power of 1.4 TW.     

Correlations in amplified four-wave mixing of matter waves

The coherence properties of amplified matter waves generated by four-wave mixing (FWM) are studied using the Hanbury-Brown-Twiss method. We examine two limits. In the first case stimulated processes lead to the selective excitation of a pair of spatially separated modes, which we show to be second order coherent, while the second occurs when the FWM process is multimode, due to spontaneous scattering events which leads to incoherent matter waves. Amplified FWM is a promising candidate for fundamental tests of quantum mechanics where correlated modes with large occupations are required.     

Suppression of the amplified spontaneous emission in ultraintense and ultrashort lasers by a highly efficient saturable absorber

For ultraintense and ultrashort laser facilities, there are few efficient and reliable methods for suppressing the amplified spontaneous emission (ASE) generated in the last several amplifiers. In the paper, we applied a highly efficient saturable absorber to suppress the ASE. Experiments were carried out to study the absorption property of the saturable absorber and the enhancement of temporal contrast with it in the front-end system of the SILEX-I laser facility with a central wavelength of 800 nm. We also analyzed the effects of the saturable absorber on other laser parameters, such as the spectrum, the spatial beam profile, and energy stability. The results show that the saturable absorber is highly efficient and the transmissivity is as high as 90%. The temporal contrast is improved by more than one order of magnitude. Meanwhile, the saturable absorber has little impact on other parameters. With these advantages, the saturable absorber is an efficient, appropriate and convenient solution to suppressing the ASE generated in the front-end system and also in the last several amplification stages for ultraintense and ultrashort lasers.     

Wave mixing and amplified spontaneous emission in pure potassium and mixed sodium-potassium vapors

We report observations of several wave-mixing and stimulated processes in pure potassium and mixed sodium-potassium vapors which are excited by a pulsed laser operating in the range 680–800 nm. When the laser is tuned to the potassium two-photon 4S6S transition, we observe stimulated emission on the various cascade transitions as well as four- and six-wave mixing. When the laser is tuned over the range 747 to 753 nm, which is well away from all atomic transitions, we observe strong forward and weak backward emission at the potassium 3D _3/24P _1/2 transition wavelength (1.17 m). However, this latter emission is only observed in the mixed sodium-potassium vapor. We present data on the excitation spectrum, forward to backward asymmetry, temporal dependence, and the laser power dependence of this emission. We speculate that twophoton photodissociation of the NaK molecule is responsible for this emission.     

Quantum statistics of the degenerate four-wave mixing process

A quantum mechanical treatment is given of the degenerate four-wave mixing process. The approximate Heisenberg equation of motion for creation and annihilation operators is solved taking into account attenuation and noise. The solution and the statistics of the modes are discussed both below and above the threshold condition.     

Intensity fluctuations of amplified spontaneous emission

The intensity fluctuations of a linearly polarized component of the amplified spontaneous emission at 3.51 μm from a single, variable-length xenon-helium source have been measured. The fluctuations are only slightly reduced despite heavy saturation and the results are found to be in qualitative agreement with theoretical models based on the coupling of the fluctuations in the beams travelling in different directions.     

Theory of travelling-wave amplified spontaneous emission

A rate-equation model for describing the travelling-wave amplified spontaneous emission pulses (TWASE) in a transversally excited travelling wave arrangement is given. 6.35 ps long ASE pulses have been obtained by 12 ps long pump pulses. The effect of pump intensity, pump-pulse duration, molecular parameters of the dyes and pump-sweep velocity on the ASE pulses is studied.     

Picosecond pulse shortening by travelling wave amplified spontaneous emission

A new scheme for travelling-wave excitation of amplified spontaneous emission (ASE) employing transversal pumping is presented. ASE pulses emitted in the forward direction had a duration of 6 ps, corresponding to one half of the pump pulse duration. The spectrum was strongly structured, with individual components having a width of 0.1–1.0 Å. Essential characteristics of longitudinal and transversal excitation of travelling wave ASE are compared.     

The output of amplified spontaneous emission lasers

The output of amplified spontaneous emission (ASE) lasers such as X-ray lasers operated without mirrors is calculated exactly for Gaussian and Lorentzian small signal gain profiles by a simple Taylor series expansion. The accuracy of the ‘Linford’ formula commonly used as an approximation for the output of ASE lasers is evaluated by comparison to our exact solutions. The Linford formula is accurate to better than 10% for intensities produced by a Gaussian gain profile, but requires multiplication by a correction factor of at gain length product greater than 5 for Lorentzian gain profiles.     

Ultra-broadband amplified spontaneous emission source by using heterogeneous optical amplifier

In this work, we propose and experimentally investigate an ultra-broadband amplified spontaneous emission (ASE) light source with 113.8 nm bandwidth (1446.2 to 1560.0 nm) by using a cascaded two-stage optical amplifier, which is consisted of semiconductor optical amplifier (SOA, 1st stage) and erbiumdoped fiber amplifier (EDFA, 2nd stage), when the output intensity is above ?35 dBm/0.01 nm. And, the EDFA only uses a 3 m long erbium-doped fiber (EDF) with a 27 mW pumping power and SOA is driven at 200 mA bias current. Moreover, the proposed amplifier also can provide a broadband gain amplification of 114 nm in the wavelengths of 1464.0 and 1578.0 nm with the noise figure distribution of 6.8 to 8.1 dB.     

Numerical study of femtosecond travelling-wave amplified spontaneous emission

The generation of pulses from amplified spontaneous emission in dye solutions is studied in the case of femtosecond pump pulses. The effects of ultrafast vibrational relaxation, self-phase modulation and optimum synchronization are discussed.     

基于四波混频过程的纠缠光放大

双模纠缠态是量子信息领域一种重要的量子资源,本文基于四波混频过程从理论上提出了对双模纠缠态的单个模式(单模放大方案)和对双模纠缠态的两个模式(双模放大方案)的放大.利用光学分束器模型来模拟在光学传输过程中损耗引入的真空场噪声,利用部分转置正定判据分析了两种不同的放大方案中四波混频过程的增益对初始双模纠缠态的纠缠程度的影响.结果表明,在特定的损耗情况下,两个方案中初始双模纠缠态的纠缠度都随增益的增大而减小,直至消失,且双模放大方案中初始双模纠缠态纠缠消失得比单模放大方案中更快.本文的理论结果为实验上实现基于四波混频过程的双模纠缠态的放大奠定了理论基础.     

Subnanosecond amplified spontaneous emission pulses by a nitrogen pumped dye laser

Pulses of 100 ps duration and peak power up to 100 kW are obtained with a dye laser pumped by an atmospheric pressure nitrogen laser of 0.5 ns duration. The shortening of the dye laser pulses is attributed to amplified spontaneous emission.     

High-power near-diffraction-limited solid-state amplified spontaneous emission laser devices

We present investigations into high-power scaling of solid-state amplified spontaneous emission (ASE) laser sources by use of two high-gain (~10(4)) Nd:YVO(4) bounce amplifiers. The sources deliver high power with a high-quality spatial output, but unlike a laser they have a high misalignment tolerance and do not require a precisely aligned cavity. In one system with two amplifiers, we demonstrate an ASE source with 24.5W of output power with good spatial quality, M(2)<2.5 in the horizontal and M(2)<1.2 in the vertical. In a more sophisticated setup, the two amplifiers are arranged in a loop configuration producing 30W of ASE output with near-diffraction-limited spatial quality, with M(2)<1.3 in the horizontal and M(2)<1.2 in the vertical, at an ~38% optical-to-optical conversion efficiency.     

Phase conjugation in fluorescein film by degenerate four-wave mixing and holographic process

Phase conjugation is performed in a fluorescein film by a cw Ar ion laser of the wavelength 0.488 μm in a degenerate four-wave mixing (DFWM) configuration. It becomes apparent that the phase conjugate wave is generated simultaneously by not only DFWM but also a holographic process and that the DFWM and holographic components of the phase conjugate wave have different time constants.     

Quantum noise generated by four-wave mixing process within a fiber ring resonator

We have analyzed the dissipative effect of the entangled photons generated by a nonlinear optical ring resonator from a non-degenerate four-wave mixing (FWM) process. The system and reservoir Hamiltonian are established in the interaction picture. To eliminate the reservoir operators, the Markov approximation is used and result them in a Linblad form in the master equation. Consequently, the positive P representation can recast this equation to the Fokker-Planck equation, and then the stochastic differential equations i.e., the entangled photon state equation of motion for photons propagating in the fiber, are obtained and easy to analyze numerically. Results obtained have shown that the entangled strength measurement depends on three main factors; first the nonlinear susceptibility of the third harmonic generation, second the damping rate that represents loss of energy from the system to the reservoir, and final the diffusion of fluctuations in the reservoir into the entangled photon modes.     

天光一号预放大器中的放大自发辐射效应

 在三维放大自发辐射（ASE）的模拟计算中，计入了侧壁反射效应以及KrF自发辐射的谱线形状（高斯型、洛伦兹型及平顶型）的影响，并对空间网点的影响进行了考察。经过综合分析，给出了ASE对预放大器放大特性影响的上、下限范围。当计入平顶型频谱分布，壁反射系数为 0 .2时，与不计入ASE的情形对比，天光一号预放大器的提取效率下降为35%。