Motion of dissipative solitons in a laser cavity with a smooth transverse inhomogeneity

The effect of the inhomogeneity gradient in a large-aperture class A laser with a saturable absorber on the transverse motion of dissipative solitons and their clusters in the laser cavity is analytically and numerically studied. A soliton with a nonzero topological charge is found to move rectilinearly in the steady-state regime but in a direction that differs from the direction of the cavity length gradient, which is connected with a nontrivial internal structure of the soliton. The steady-state motion of soliton clusters can be curvilinear, including translational and rotational motions of their center.     

Generation regimes of a pulsed Nd:YAG laser with transverse LED pumping and multiloop self-pumped phase-conjugate cavity

The generation regimes in a pulsed Nd:YAG laser with transverse LED pumping and multiloop self-pumped phase-conjugate cavity on the gain gratings are studied. The differential efficiency of laser is 27% in the free-running regime at a pulse energy of up to 1 J and quality parameter M ² of no greater than 1.5. The pulse energy under passive Q-switching is no less than 60% of the pulse energy in the free-running regime at the same beam quality. The generation of the narrow-band radiation is demonstrated. A generation band of no greater than 1.2 GHz corresponds to the primary single-frequency high-power laser pulse in the free-running mode under conditions for self-Q-switching on the gain gratings. When additional elements (F ₂ ^? :LiF and Cr⁴⁺:YAG crystals) are introduced in the optical scheme of the phase-conjugate cavity, similar narrowband single-mode generation is observed in the passive Q-switching regime as a pulse train or monopulse. The laser pulse power is up to 2 MW at a pulse duration of 20 ns.     

On localized structures of radiation in a wide-aperture laser with a transverse inhomogeneity

The analysis of the stability of the generationless regime in a laser with a smooth transverse inhomogeneity of the resonator length is performed. Localized structures of radiation are considered that are possible in this laser when the nonlinearity of the gain and of the refractive index of the medium is taken into account.     

Two-mode operation in a laser with nonlinear mirror

The operation of two modes in a multistable laser is examined. One of the modes is treated as a perturbation and the stability of the oscillating mode is analysed. We find that the perturbing mode can switch the oscillating mode from one state to the other state of lower intensity. We also find that for a certain choice of steady-state parameters the system might exhibit self-pulsing or chaotic behaviour.     

Variation of laser photon statistics with cavity length

It is demonstrated by photon counting measurements that the light from a He:Ne laser becomes increasingly coherent if the cavity length is increased while the resonance frequency is kept constant. The difference between theories based on plane wave modes and gaussian shaped modes is resolvable.     

Linear cavity Brillouin fiber laser with improved characteristics

A configuration for linear cavity Brillouin fiber laser (BFL) generation is demonstrated using a standard single-mode fiber, two optical circulators, a 3 dB coupler, and a 95/5 coupler to allow high efficiency. With a Brillouin pump (BP) power of 13 dBm, the laser peak power is 12.3 dB higher than a conventional linear cavity BFL at an upshifted wavelength of 0.086 nm from the BP wavelength. In addition, it is revealed that the BFL peak power can be higher than the transmitted BP peak power when the BP power exceeds the second Brillouin Stokes threshold power.     

External cavity operation of the spin-flip Raman laser

Continuous wave, external cavity operation of the InSb spin-flip Raman laser has been achieved. Additional cavity interactions have been identified and their influence is considered.     

Coherence and saturation properties of second-harmonic generation with a nonlinear crystal inside the laser cavity

The basic equations for second-harmonic generation including noise are derived for the case that the nonlinear crystal is put inside the laser cavity. A realistic model of a (detuned) laser with two-level atoms in single-mode operation is taken using the nonlinear theory of laser noise which describes the laser saturation effects, the phase diffusion and the intensity fluctuations. The reaction of the second-harmonic field on the fundamental field is taken into account as well as the reaction of the fundamental field on the laser. The nonlinear crystal is described by microscopic anharmonic oscillator equations (without introducing nonlinear susceptibilities by perturbation theory). The saturation of the polarization of the nonlinear medium is taken into account exactly with the only assumption that the influence of third and higher harmonics should be small. The electromagnetic field is described semiclassically by stochastic equations. In all equations, the damping is introduced simultaneously with Markoffian fluctuating forces by coupling to heatbaths. The equations are solved exactly in the stationary state without noise (the time dependent solution including noise will be presented in a subsequent paper). The most important saturation effect is a frequency shift which depends on the laser intensity.     

Calculation of the focal length of a thermal lens inside a laser cavity

A formula has been found for the value of the induced thermal lens focus in a cell containing liquids with low absorption coefficients, inside a laser cavity. Refraction laws, and in extent, transport equations for progressive and regressive waves with gaussian profile, have been obtained in the geometrical optics approximation. The stationary case is considered, with energy transfer by conduction. The relationship found is compared with results from other works and discussed.     

Stable mode-locking operation in a Cr:forsterite laser with a five-mirror cavity

The experimental finding of more-stable mode-locking operation in a five-mirror cavity than in a conventional four-mirror cavity for a Cr:forsterite laser [IEEE J. Quantum Electron. 33, 1975 (1997)] was interpreted by ABCD-matrix formalism. Since the optimum cavity configuration operation for mode-locking operation was attainable in the middle of the stable cavity condition, we conclude that one can easily achieve KLM alignment and stable mode locking with a five-mirror cavity.     

Picosecond laser oscillator with a cavity design for stable CW mode-locking operation

A detailed design of a picosecond laser oscillator is made by using optical resonance theory and semiconductor saturable absorber mirror continuous wave mode-locked technology. Mode parameters in the optical resonance including beam sizes on the laser crystal and mode locker are calculated. By theoretical calculations, 3.7 W output power is obtained at a pump power of 11 W and the optical to optical efficiency is 34% in the designed model of picosecond laser. Based on the detailed design, an experiment is proceeded and a picosecond laser oscillator of about 3.5 W output power with 10.6 W pump power is fabricated. The optical to optical efficiency of the laser is 33%, the pulse duration is about 20 ps, and the repetition rate is about 80.3 MHz. The oscillator presents long-term stability in the experiment.     

Spectral characteristics of an open cavity with a metal-dielectric inhomogeneity

We propose a new method for studying the spectral characteristics of open cavities containing circular metal-dielectric cylinders. As a result, an algorithm for calculating the natural-frequency spectrum of such a class of electrodynamic structures is developed. A numerical comparative analysis of the spectral properties is carried out for a two-mirror, confocal, open cavity with a circular metal-dielectric cylinder and a similar cavity with the corresponding radial-layered dielectric cylinder. Acad. A. Ya Usikov Institute of Radiophysics and Electronics of the National Academy of Sciences, Kharkov, Ukraine. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 10, pp. 1336–1347, October 1998.     

Linear cavity fiber laser with 100 nm wavelength tuning range

We report a 100 nm widely tunable double-clad Ytterbium doped fiber laser. The fiber laser has a linear cavity configuration, where the feedback is provided by a Sagnac fiber mirror on one side, and an external bulk grating on the other side. On the bulk grating side, the fiber has a balled curved-core-termination that suppress backreflection by roughly 50 dB, and does not affect the pump coupling efficiency. The tuning range goes from 1055 nm through 1155 nm, with a maximum output power of 360 mW at 1080 nm, and 0.3 nm linewidth.     

Low-divergence operation of a long-pulse excimer laser using a SBS phase-conjugate cavity

The use of an optical cavity containing a stimulated Brillouin scattering (SBS) phase-conjugate reflector to control the spatial and spectral output of a long pulse (>100 ns) X-ray preionized XeCl laser is reported. The divergence of the 3×4 cm² output beam has been improved by a factor of 20 to <150 rad. The temporal form of the output depends on the acoustic decay times of the liquid and gaseous SBS media used. Four-wave mixing via gain saturation has been observed within the discharge volume, leading to depolarisation of the output beam.     

High power single transverse mode operation of a tapered large-mode-area fiber laser

To get high output power with good beam quality, a tapered section is introduced to large-mode-area (LMA) Yb-doped fiber laser. Output characteristics of the fiber laser without tapered section and with tapered section are compared experimentally. When the launched pump power is 119.1 W, 77.9 W with M² 3.08 and 56.4 W with M² 1.14 can be obtained, respectively. The corresponding slope efficiencies are 71.8% and 54.1%, respectively. Although output power of the tapered fiber laser has 30.6% penalty, brightness of it is as much as 5.28 times of the fiber laser without tapered section. Moreover, spectra of them are measured. It is found that tapered section makes lasing wavelength of the fiber laser shorter.     

异面腔四频差动激光陀螺的智能选模

针对异面腔四频差动激光陀螺(DILAG)工作模式不确定性和跳模对其性能的负面影响,提出了根据开机时腔体温度快速选择最优初始模的智能选模方法。分析了纵模阶数对DILAG的零偏和比例因子的影响以及跳模的危害,指出选择最优初始模是在现有基础上进一步提高DILAG性能的重要方法。通过温度实验做出了最优模相应的压电换能器(PZT)驱动电压随温度的变化曲线,为建立选模模型提供了基本依据。实验表明,智能选模使腔长控制系统加电后能快速稳定在最优初始模,减小了跳模几率,提高了腔长控制电路的鲁棒性和自适应性,对改善DILAG的性能、可靠性具有实用价值。     

Distortion of waves with profile discontinuities in the medium with a periodic transverse inhomogeneity distribution

For the purpose of describing the joint influence of nonlinear effects and refractive inhomogeneities on the evolution of intense acoustic waves, a model of the medium the local velocity of sound of which is periodic in the transverse direction and decreases in the propagation direction, which generalizes the known models of the layered medium and of the infinitesimally thin phase screen, is proposed. An exact solution is found for the wave with arbitrary initial conditions: time profile and transverse profile. The spatial wave structure in the inhomogeneous medium is calculated; it is shown that narrow high-amplitude regions are formed and the rate of nonlinear effect accumulation changes. It is shown that the amplitude of the wave at long distances from the source may differ little from its initial value due to compensation for the effects of nonlinear attenuation and of focusing by inhomogeneities. Possibilities of amplification of intense waves depending on the proportion between parameters of the wave and those of the inhomogeneous medium are studied.