Photon statistics in harmonic generation processes with a weak input chaotic field

The time evolution of the normally ordered photon number variance of the fundamental mode inm-th harmonic generation processes in the case of a weak input chaotic field is considered. It is shown that the fundamental mode may reveal sub-Poissonian photon statistics, however, in the course of second-harmonic generation solely.This work was carried out within the program No 2 0150 91 01 of the Polish Committee for Scientific Research.     

Peculiarities of self-action in second harmonic generation of laser radiation in nonlinear crystals

By using the generalized method of strong interaction of nonlinear waves and computer simulation, an analysis of the influence of self-action effects on second harmonic generation of an intense diverging picosecond pulse is performed. Using the approximation of strong wave interaction, an analytic solution is obtained for frequency conversion of the laser radiation taking into account the pump intensity depletion, the influence of the angular dispersion effect (ADE), and the higher nonlinearities. It is shown that the self-action effects, the ADE, and the linear phase mismatch can compensate for each other, increasing the efficiency of second harmonic generation. Optimum conditions for second harmonic generation in converging and diverging laser beams were found. An asymmetry of the angular dependence of the second harmonic intensity was experimentally observed and theoretically explained. The asymmetry is caused by the reverse energy conversion of the second harmonic into the pump by the influence of the ADE and Kerr nonlinearities.     

Phase effects at second harmonic generation of powerful laser radiation in noncentrosymmetrical media

There has been developed the theory of second harmonic generation of the intensive laser fields in the existence of both quadratic and cubic polarization in medium in the constant-intensity approximation accounting for the reverse effect of the excited wave on the exciting one and simultaneously allowing us to take into account phase mismatch and the damping of all the interacting waves. It is shown that the changes of pump intensity through self-phase and cross-phase modulation processes effect optimum phase relationship between interacting waves, the change of the spatial beating period. The conditions of compensating undesirable phase shifts between interacting waves have been determined, the analytical expressions for calculation of optimum values of phase mismatch, length of noncentrosymmetrical medium and the spatial beating period are offered. It is shown that in the absence of linear phase mismatch with an increase of basic radiation intensity the spatial beating period is being reduced. The numerous analysis has been made of frequency doubling process efficiency for KDP and LiNbO₃ crystals.     

Self pulsing in second harmonic generation

We consider nonlinear optical processes in a cavity maintained far from thermal equilibrium by external pumping. In second harmonic generation we predict a hard mode instability at a critical pump strength indicating the existence of undamped spiking similar to that in strongly pumped lasers. In subharmonic generation above the soft mode transition noted by Graham we predict the appearance of sidebands in the subharmonic spectrum.     

Noncollinear second harmonic generation in KDP

This paper reports experimental and analytical results on optical second harmonic generation when a noncollinear arrangement is employed. The dependence of second harmonic power on crystal length, absorption, beam radius and the angle between the two fundamental waves is obtained. Double refraction of the crystal is taken into account, but the divergence and depletion of the fundamental waves are neglected. The results of the calculations are confirmed by experiments carried out with a KDP crystal in the near field of two intersecting TEM₀₀ ruby laser beams.An extension of the theory to nonlinear interactions other than second harmonic generation - e.g. four-wave interaction - is possible.     

Efficient second harmonic generation in CDA

Efficient second harmonic generation at 0.532 μ has been achieved in a temperature tuned CDA crystal when a narrow beam divergence Nd:YAG laser was used. At a crystal temperature of 40.3°C, a peak second harmonic power of 7.5 MW was obtained with a peak power conversion efficiency of 33%. The temperature variation of the refractive indices in CDA has been determined to be d(n^e_2ω?n⁰_ω)/dT = 7.2 × 10^?5°C^?1.     

Photon bunching and antibunching in second harmonics generation

A nonperturbative, numerical study of photon statistics in second harmonics generation is presented.     

Optimum conditions for the generation of the second harmonic of intense laser radiation

A generalized approximation of strong interactions of waves is suggested for the theoretical analysis of second-harmonic generation under conditions of self-action. On the basis of the method suggested, approximate solutions for the efficiency of second-harmonic generation are obtained with regard to the influence of higher nonlinearities, depletion of pumping radiation, and linear phase mismatch. The effects of the phase mismatch and the spatial distribution of the amplitude of the fundamental harmonic on the efficiency of second harmonic generation by intense laser radiation is analyzed. The results obtained with the approximate method developed are shown to be in good agreement with known experimental data and numerical calculations. Optimum conditions for second harmonic generation are determined in a wide range of laser radiation intensity and at different spatial distributions of the fundamental harmonic amplitude.     

Watt-class green-emitting laser modules using direct second harmonic generation of diode laser radiation

Large-area high-resolution displays, using a flying-spot to create the picture, require light sources in the red, green and blue wavelength range with a high optical output power and nearly diffraction limited beam. In this paper we present experimental results of high-brightness distributed Bragg reflector tapered diode lasers at 106x nm that can be used for single-pass second harmonic generation into the green. Based on these lasers we developed compact (2.5 cm³) green laser modules with an output power of 1W at 53x nm and an electro-optical conversion efficiency of about 5%. The output power stability is better than 2% and the wavelength stability is ±10 pm. The excellent beam quality M _?? ² < 2 of the green light allows operation in flying spot application systems. Furthermore, we estimate that our concept allows power scaling up to 2W by using nonlinear planar waveguide crystals and into the multi-watt level by spectral beam combining.     

二次谐波产生过程中准相位匹配条件的研究

从耦合波基本方程出发,在实空间严格推导出二次谐波产生(SHG)过程中的准相位匹配(QPM)条件.讨论了满足QPM条件时,SHG的转换效率以及相位失配角随波传播距离的变化.着重研究了非线性极化率的周期性调制对提高SHG转换效率的贡献.     

Optical second harmonic generation in ammonium tartrate

Second harmonic generation was observed in ammonium tartrate single crystals by a phase matching technique at the fundamental wavelength 1.153 μm. The nonlinear coefficients were found to be comparable in magnitude to those of KDP. The optical transmission and the refractive indices were also measured.     

Mode-coupling phenomena in intracavity second harmonic generation

The dependence of intracavity second harmonic generation efficiency on the linear phase detunings in crystal and air is studied both theoretically and experimentally. It is shown that in the presence of feedback at the second harmonic frequency an optimum conversion efficiency can be achieved by a mutually correlated choice of phase mismatch in a nonlinear crystal and the position of the latter inside the cavity.     

Optical second harmonic generation in ammonium malate

Second harmonic generation in ammonium malate has been investigated in a wavelength region between 492 nm (short wavelength limit of the harmonic beam at 246 nm) and 640 nm. Phase match angle, refractive indices and all coefficients of the nonlinear susceptibility tensor have been measured; several possibilities for phase matching are discussed.     

On the theory of second harmonic generation

It is shown how the theory of non-linear interaction between the modes of the open resonator, developed previously [1] and used to study resonant second harmonic generation [2], can be applied to second harmonic generation in the absence of a resonator. The conditions under which the second harmonic output, in the small conversion approximation, can be approximated by a Gaussian beam are derived.The optimum value of the focusing parameter I/z₀ (hereI is the length of the crystal, andz ₀ is one-half the confocal parameter of the fundamental beam) for the total output is shown to be 5.68 agreeing precisely with the value given by Boyd and Kleinman [3].     

Higher-order squeezing and photon statistics in fourth harmonic generation

Squeezing of the electromagnetic field is investigated in fundamental mode in fourth harmonic generation under a short time approximation based on quantum mechanical approach. The occurrence of squeezing in field amplitude and in higher power amplitude (up to fourth-order) in fundamental mode has been studied. It is found to be dependent on phase of field amplitude of the fundamental mode. The dependence of squeezing on the photon number has also been investigated. It is found that squeezing increases non-linearly. It has also been found that the photon statistics of the field in fundamental mode is sub-Poissonian. The signal to noise ratio has been studied in different order. It is found that signal to noise ratio is higher in lower order.     

Precision analysis in polarization-resolved second harmonic generation microscopy

Polarization-resolved second harmonic generation (PSHG) imaging microscopy allows one to provide information such as anisotropy parameters and molecule orientation. We analyze the precision of parameter estimation for samples with cylindrical symmetry and a Gaussian additive noise model. We introduce improvements of existing techniques that can be useful to get rapid acquisition and processing of PSHG images, and we discuss the influence of photon noise.     

Internal second harmonic generation in InGaAsP DH lasers

Self induced second harmonic generation (SHG) accompanying 1.3 μm lasing radiation was first observed in fundamental transverse mode InGaAsP DH lasers. Sum frequency generation by two lasing longitudinal modes was observed, which has a conversion factor of four times greater than that for SHG by a single lasing longitudinal mode and predicts the simultaneous laser oscillation of the several longitudinal modes. The estimated second order nonlinear susceptibility of In_0.76Ga_0.24As_0.55 P_0.45 was about 5 × 10^-20 in rotationalized MKS unit, which is at least an order of magnitude greater than that of GaAs.