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Ustawodawca z różnych przyczyn przekazuje do rozpoznania przez sądy powszechne sprawy administracyjne. Sprawy te załatwiane są przez organ administracyjny decyzją, a odwołanie kierowane jest do sądu powszechnego. Przykładem takiej procedury, zwanej hybrydową, jest postępowanie w sprawach z zakresu ubezpieczeń społecznych.

We investigate the influence of thermally induced higher order aberrations on the fundamental mode of a rod solid-state laser. The perturbations of the laser due to the most common aberrations (spherical aberration and astigmatism) are studied for several sizes of the fundamental mode. Results concerning the additional losses and beam quality degradation induced by these aberrations are also presented and demonstrate that for a large overlapping of the beam size and the laser rod, the spherical aberration amplitude must not exceed 0.5λ for the cavity to oscillate. The influence of gain saturation also analyzed in the model is shown to be of less importance.

The influence of absorption or gain on the Bragg diffraction efficiency of intracavity refractive index gratings is analyzed. Losses drastically reduce the diffraction efficiency of the device which can nevertheless be optimized in order to limit their inauspicious influence. On the contrary, in amplifying intracavity media very large diffraction efficiencies are obtained even with small integrated refractive index modulations. The optimization of the device for maximum diffraction efficiency or vanishing reflectivity could find applications in tunable lasers and in high contrast amplifying optical signal processing.

We report a giant photoinduced Faraday rotation in a $\mathrm{CdTe}/{\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Te}$ multiple quantum well structure when the laser frequency is tuned close to the fundamental excitonic transition of the quantum well and saturation sets in. At the same time we observe stimulated emission and buildup of magnetization through photon spin recycling in the presence of a magnetic field which was analyzed by a time-resolved linearly polarized pump and probe technique. The magnetization buildup is also seen in the absence of the seeding magnetic field and by using a circularly polarized pump beam.

Abrege: Nous etudions les nonlinearites de rotation de polarisation et d'ellipticite d'une microcavite de semiconducteur, contenant 18 puits quantiques, en regime de couplage fort ou la resonance excitonique du materiau intracavite et celle de la cavite sont en forte interaction. Les experiences sont realisees grâce a un generateur-amplificateur parametrique optique pompe par un laser Nd:YAG « Picoseconde », et les mesures effectuees par un systeme de detection compose de deux balances optiques. Le resultat des mesures montrent qu'une rotation Kerr de l'ordre de 1,4 ° a lieu a temperature ambiante sous un champ magnetique de 1,4 kG.

We consider the Raman amplification problem for silicon waveguides in the regime in which both the pump and signal pulses are relatively short but wide enough that their duration exceeds the phonon lifetime (about 3 ps in silicon). We use the coupled pump-signal equations for numerical simulations that include all competing nonlinear effects such as self- and cross-phase modulations, two-photon and free-carrier absorptions, and changes in the refractive index induced by the free carriers. However, numerical simulations do not provide much physical insight. For this reason, we also develop an approximate analytic approach for solving the Raman amplification problem. We introduce the concept of an effective Raman gain and show analytically how it depends on the pump bandwidth. As the pump spectrum broadens inside the silicon waveguide, the effective Raman gain is reduced considerably. We obtain an analytical form of the nonlinear phase accumulated during propagation inside a silicon waveguide and use it to calculate the total spectral broadening experienced by a pump pulse. Using this result, we can predict changes in the effective Raman gain as a function of pump pulse energy. A comparison of our predictions with the recent experimental data shows that our model is reasonable and captures the essential physics.

The giant Faraday rotation (larger than 90°) photoinduced in ZnMnTe or CdMnTe by picosecond duration pump pulses is analysed by the time-resolved pump and probe technique. Slow thermal and fast photocarrier-induced processes are found to occur depending on the choice of the semimagnetic semiconductor sample.

The nearly degenerate four-wave mixing technique is used to investigate the physical origin of period doubling in the route toward chaos. This spectroscopic approach identifies resonantly enhanced nearly degenerate four-wave mixing processes as being responsible for the generation of subharmonic frequencies. The technique presented in the case of GaAlAs semiconductor lasers could be applied to the study of monomode instabilities occurring in any laser or bistable devices.

High-efficiency pulse compression has been obtained by using an externally pumped intracavity Raman oscillator. Through stimulated Raman scattering, the energy of a primary, long-pulse-duration omega(L) laser is downconverted and stored at the first Stokes frequency omega(1s) in a high-Q cavity containing the Raman medium. Then this electromagnetic energy is quickly extracted at the second Stokes frequency. This technique, which uses hydrogen gas as the Raman medium, permits a 25-nsec-duration ruby-laser pulse shortening by a factor of 12.5 with a near 50% quantum efficiency. Contrary to the case of intracavity Raman oscillators or amplifiers, this method can also be used with absorbing laser media.

Very-high-efficiency (80%) Raman amplification of a narrow-band injected Stokes signal has been achieved in the case in which pump and Stokes linewidths are both narrower than Raman transition width. Under such conditions, the Stokes-beam amplification is obtained without line broadening, permitting the creation of widely tunable powerful monochromatic sources when tunable lasers are used. With fixed-frequency pump lasers, tunability within the Raman linewidth has also been demonstrated. With a pump linewidth much broader than that of the injected Stokes signal, a spectral compression rate up to 16 has been achieved by using this Raman amplification technique.

International audience; A very simple model has been developed to describe the diffractive properties of a crossed grating structure of the refractive index formed by a thin transmission grating recorded in a Bragg reflector. When the Bragg condition of the transmission grating coincides with the band edge of the reflection grating seen as a one dimensional photonic crystal, the diffraction efficiency and wavelength selectivity of the transmission grating are highly enhanced and a Bragg diffraction regime can be obtained, even in very thin samples. The model can be used to design micrometric very efficient new diffracting devices for optical signal processing

Recent developments in the field of nonlinear optics with photonic crystal fibers have led to the realization of supercontinuum spectra or parametric sources of correlated photons. However the nonlinearities were still limited by the use of silica. Hollow core photonic crystal fibers (HCPCF) filled with highly nonlinear liquids or gases enable the implementation of more performing nonlinear devices and open the scope of potential applications thanks to the large variety of usable liquids and gases. Moreover liquid and gas filled HCPCF present several original propagation properties such as transmission bands that can be tailored to favor or prevent a given nonlinear mechanism. In this work we will show that the on-purpose limited transmission band enables a high conversion efficiency towards a single Stokes component even at high pump intensities. Moreover such Raman converters generate single spatial mode at specific wavelengths that can be determined to fit desired applications.

Non-linear Faraday processes occurring at high laser intensities are experimentally demonstrated in a Cd 0.75 Mn 0.25 Te alloy. Both the polarization direction and the phase of the incident beam are modified through the non-linear interaction. The large non-linear susceptibilities measured for the material show that non-linear Faraday processes overcome two-photon absorption and Kerr effects for magnetic field of the order of few teslas.

Nonlinear Faraday processes occuring at high laser intensities are experimentally demonstrated in a Cd 0.75 Mn 0.25 Te alloy. Both the polarization direction and phase of the incident beam are modified through the nonlinear interaction. The large nonlinear susceptabilities measured for the material show that nonlinear Faraday processes are expected to overcome two-photon absorption and Kerr effects for magnetic field of the order of few Tesla.

International audience; Highly improved diffraction properties are demonstrated in a two-dimensional [2D] grating consisting of a transmission grating optically recorded in a semiconductor one-dimensional photonic crystal (1D-PC). Near unity internal diffraction efficiency, high wavelength selectivity, and Bragg diffraction regime operation are demonstrated when the read beam is set at Bragg incidence on the transmission grating while its wavelength corresponds to the band edge of the 3 um thick 1D-PC. When the 2D grating is grown on a Bragg mirror, a single diffracted beam is obtained, which makes the device promising for optical signal processing

5 pages; International audience; An optical parametric oscillator for the infrared region pumped by a picosecond Ti:Sapphire laser is demonstrated. Fourier transform limited pulses of 15 and 10 ps, for signal and idler wavelengths respectively, have been obtained using a periodically poled stoechiometric lithium tantalate nonlinear crystal, without any spectral filtering. A complete experimental study of the influence of the cavity length detuning on the spectral and temporal dynamic of the output radiation is discussed.

International audience; Raman amplification of optically carried RF signals is shown to be a good alternative to erbium-doped-fiber amplification. In the case of continuous RF signal, RIN levels as low as -160 dB/Hz, limited by the laser source, are obtained. Moreover, when the RF signal is no more continuous, such as real radar waveforms, we evidence that Raman amplification overcomes erbium-doped-fiber amplification. Improvement of the pulse-to-pulse RF phase stability of 17 dB is observed. This result is attributed to the nature of Raman amplification, which does not involve transient variations of the population inversion across the whole spectral range covered by radar waveforms.

Optical limitation in resonant Faraday media sandwiched between crossed polarizers is analyzed both theoretically and experimentally. In this technique resonant Faraday rotation permits a net transmission at low intensity levels, whereas the setup transmission is quenched at higher intensities when the active transition is completely saturated. This technique offers many advantages, such as a very low fluence threshold (~12 nJ/cm(2) in cesium vapor), a high intensity range (more than 4 orders of magnitude for polarizer losses of 10(-5)), and quasi invulnerability to optical damage, which make this technique attractive for the protection of fixed-wavelength operated detectors.

International audience; We report the results of an experimental investigation of the diffractive properties of a thick index grating embedded in a Fabry-Perot resonator, the so-called intracavity Bragg grating. We compare the performance of this device with that of a bare Bragg grating with same thickness and the same index modulation and establish the improvement in performance with the resonator. The experimental data also fit predictions calculated from a theoretical model.

International audience; Intracavity gain gratings are theoretically demonstrated to exhibit diffraction efficiencies that are 100 times larger than unity at pump powers substantially below the lasing threshold. Experiments performed using a Nd:YVO4 microlaser pumped below threshold by two interfering Ti:sapphire laser beams are described. Huge enhancement of the diffraction efficiency (5000x) and a large increase of the angular selectivity (10x) are demonstrated despite the angular reduction of the Fabry-Perot cavity finesse. Much better results are expected using gain gratings with larger areas or thinner cavities such as vertical cavity surfaceemitting lasers. Such large fan-out values could be very interesting for applications to optical signal processing.

International audience; We experimentally and theoretically analyze an original method based on two-wave mixing in an erbiumdoped fiber amplifier for optical carrier reduction of microwave signals. 75% optical carrier attenuation has been observed, and a 10 dB modulation depth increase of the microwave signal is experimentally demonstrated. Moreover, calculated results are in good agreement with measurements and predict that up to 80% carrier attenuation is easily possible.

We demonstrated experimentally the feasibility of a fast tuning high resolution filter with a good flatness. The device could easily be adapted to applications in spectroscopy or in DWDM communications (tunable lasers or filters for instance). Acousto-optic filtering has been extensively studied because its tuning rapidity makes it very useful for many applications. Nevertheless, its resolution is often not sufficient in the fields of telecommunication or spectrometry. The proposed grating-assisted acousto-optical filtering technique combines the high resolution of diffraction gratings (/spl sim/10 pm) and the tuning swiftness of acousto-optics (/spl mu/s).

In this paper, we propose to investigate the case when both the incident beam and the main diffraction order are Fabry-Perot resonant, at Bragg incidence on a thin unslanted grating. We calculate the intensities of the most important diffraction orders and show what conditions must be fulfilled to obtain a Bragg diffraction regime where all diffracted energy is concentrated in a single diffraction order

We present a theoretical study and an experimental demonstration of stimulated Raman effect in a hollow core photonic crystal fiber filled with a low index nonlinear liquid (ethanol).

International audience; Stimulated Raman amplification of optically carried microwave signals in optical fibers is experimentally investigated. In the backward configuration which is shown to be less noisy than the forward one, net amplification factors larger than 20 dB are demonstrated in the low signal regime with better relative intensity noise (RIN) values than using erbiumdoped fiber amplifiers. Due to the RIN flatness with respect to the gain of the stimulated Raman amplifier high quality variable gain amplification of optically carried microwave signals could be implemented using optimized Raman amplifiers

International audience; We show that high efficiency stimulated Raman scattering can be obtained using hollow core photonic crystal fiber with the core filled with a low refractive index nonlinear liquid. This new architecture opens new perspectives in the development of nonlinear functions as any kind of nonlinear liquid media can now be used to implement them, with original properties not accessible with silica core fibers

International audience; The diffraction regime of a thin grating inserted in a Fabry-Perot cavity is investigated. Our calculations show that, at Bragg incidence, a single diffraction order can be selectively enhanced, giving rise to a very efficient Bragg-like diffraction regime. The optimization of the device is studied as a function of the resonator thickness and finesse and the grating position inside the Fabry-Perot cavity. The angular and wavelength selectivities are also investigated. The device could be easily integrated and would be very useful for optical signal processing applications.

In this paper, we present single-mode SBS laser, based on an all-fiber short cavity, simultaneously resonant for pump and Stokes waves for radiofrequency applications. All-fiber stimulated Brillouin scattering (SBS) lasers can be good candidates to fulfill both of these requirements.

Large photoinduced Faraday rotations of the polarization direction of a probe beam traveling through a semimagnetic semiconductor are obtained at temperatures higher than that of liquid nitrogen when a pump pulse is sent through the material. These rotations are quasiproportional to the photoinduced free‐carrier density and the applied magnetic field and are strongly resonant with the band‐gap‐probe frequency detuning. A model based on the free‐carrier induced saturation of the refractive indices explains well the experimental observations. The high values obtained for the photoinduced polarization rotations (more than 1° pJ−1 μm2) make such a process attractive for the design of optical signal processing devices.

Summary form only given. Amplification of the intracavity medium hugely enhances the diffraction efficiency of intracavity Bragg gratings. The device can be optimized for optimum diffraction efficiency (with diffracted intensity 1000 times larger than the incident one) or for null reflected signal (with diffraction efficiencies larger than 1000%). This could be of importance for tunable lasers and optical signal processing.

We investigate the influence of thermally induced spherical aberrations on the fundamental mode of a rod solid-state laser. Results concerning the additional losses and beam quality degradation are presented and point outthat for a large volume fundamental mode resonator, a spherical aberration greater than O.5X dramaticallydeteriorates the laser performances. To control the resonator performances, we present a new phase control technique with an intracavity opticallyaddressed liquid-crystal spatial light modulator. The presented Nd:YAG resonator is able to deliver beams withvarious spatial profiles, as flattop super-Gaussian or square-shaped beams, and is thus potentially able tocompensate for the thermally induced aberrations of the laser medium.Keywords : thermal aberrations, laser rod resonator, beam shaping, liquid-crystal devices 1. INTRODUCTION With the recent development of high-brightness, high-power solid-state lasers, requiring up to kWatts ofpumping power, the analysis of the influence of the higher order aberrations of the laser rod thermal lens on theperformances of the resonator is becoming a crucial point in the development of high-brightness sources 2 Therealization of an efficient TEM00 resonator implies an optimized overlap of the fundamental mode of the cavitywith the gain region in order to increase the volume of the active material involved in the laser action

International audience; The grating thickness limit lFP between the Raman-Nath and the Bragg diffraction regimes is calculated for an index grating placed in an asymmetric Fabry-Perot resonator with a totally reflecting back mirror and compared with that which was obtained for the same grating with no cavity lM . Owing to the increase of the effective interaction length inside the Fabry-Perot cavity, the stronger the front mirror reflectivity R1 of the cavity, the smaller the thickness above which the whole diffracted intensity can be concentrated into one unique diffracted beam: lFP=[(1−√R1)/(1+√R1)]lM/2.

Very efficient gratings can be recorded in semiconductor media due to thc hugc dependance of the rcfrilctive index with respect to carrier density. However. due to the fast diffusion of thc photogenerated carriers, the lifetime of these gratings is small (from the picosecond to the nanosecond range). In this paper. wc show that long-lived (T > Ips) gratings can bc recorded in CdMnTe awing to the efficient trapping of electrons on mangancse sitcs [I], which generates U grating of fixed ncgativc chnigcs whcn the crystal is illuminated by an interference patlcrn. Neutrality requiring the existencc of a hole grating then c~eates a hole induced refractive index grating. Griltinga were recorded ~n a 3 mrn thick CdMnTc ramplc by the interference pattern of two "write" pulsesdslivered by the same dye laser pumped by a frequency doubled Q-switched KdYAG laser. The time evolution of the diffracted signal obuined from B ~ontin~ous "read" lacr diode WE rcgistcrcd for various grating wavelcngths A (sce figure i(a) as an example). The corrcsponding inverse of the grating lifetime 11% is plotted in figure I(b) as B function of A-?

Le regime de diffraction d'un reseau infiniment mince insere dans une cavite Fabry-Perot est etudie, en particulier en fonction de la longueur de la cavite. Un regime de Bragg tres efficace est possible meme en utilisant des cavites micrometriques, ce qui peut etre utile pour le traitement optique de l'information.

We propose nonlinear Faraday rotation as a mechanism for achieving stable polarization mode locking of a soliton laser. We analyze by perturbation theory and beam-propagation simulations the interplay between bandwidth-limited gain, gain dichroism, and linear and nonlinear Faraday rotation.

We experimentally and theoretically study self-phase modulation by Kerr effect in a liquid filled hollow core photonic crystal fiber. We perform a complete characterization of the linear optical properties of the hollow core photonic bandgap fiber filled with deuterated acetone to determine all the characteristics of the propagation mode. The nonlinear coefficient of the fiber is determined by fitting the output spectra broadened by self-phase modulation with a new analytical expression giving the spectra of a hyperbolic secant pulse transmitted through a Kerr medium. The experiment allows a precise determination of the nonlinear index change nI2 of acetone-d6 equal to (1.15±0.17)×10−19 m2 W−1.

A fast tunable filtering technique is proposed associating a diffraction grating with an intracavity Bragg grating. The bandwidth and the tuning range of this filter can be easily adapted by changing the diffraction grating's orientation, or its period, and its response is uniform over the whole tuning range. A numerical simulation of the filter response to a Gaussian beam has been developed, and it fits the experimental results allowing a calculation of the performances that could be obtained with more specific elements. For example, using a commercial acousto-optic deflector would allow a separation of 500 frequencies. It would then be possible to have a tuning range of 100 nm with a bandwidth of 0.2 nm for optical telecommunications.

Two-dimensional photonic crystals composed of two orthogonal volume diffraction gratings have been photogenerated in photopolymers. When the read beam is set at the Bragg angle, the diffraction efficiency of the transmission grating is strongly enhanced at the band edge of the reflection grating recorded in the material. Such a device provides Bragg operation and enhancement of the diffraction efficiency of the thin diffraction grating together with good wavelength selectivity. Such advantages could be interesting for optical signal processing.

A solution for dynamically enhancing the modulation depth of optically carried microwave signals is presented. It is based on stimulated Brillouin scattering in photonic crystal fibres (PCFs) used in loop configuration. The behaviour of this nonlinear effect in this new type of fibre is compared, both experimentally and theoretically, to that observed in conventional optical fibres.

Nonlinear Faraday processes in diluted magnetic semiconductors are theoretically and experimentally investigated through the analysis of the modifications of the intensity, the polarization direction, and the phase of a high-intensity arbitrarily polarized laser beam. Calculations demonstrate that the nonlinear Faraday processes are decoupled from Kerr effects when the propagation wave vector is in the (1, 1, 1) direction with respect to the crystal axes. Experiments performed in such a configuration in Cd0.75Mn0.25Te confirm this analysis and show photoinduced polarization rotations and phase changes proportional to the magnetic field that saturate when the laser intensity is increased beyond a certain value. The large nonlinear susceptibilities derived for the material show that the nonlinear Faraday processes could overcome two-photon absorption and Kerr effects for magnetic fields of the order of a few tesla.

Intracavity nearly degenerate four‐wave mixing has been demonstrated by injecting a low intensity probe beam of frequency ω−δω inside a (GaAl)As semiconductor laser operating above threshold at the pump frequency ω. Conjugated reflectivities as high as 5000 together with a 25% energy conversion efficiency are reported with only a few milliwatt pump power. Additional peaks related to the ac stark effect have been observed at a detuning which depended on the pump power. This process could be useful for the study of instabilities occurring in lasers as well as for optical amplification in laser diodes.

Millijoule energy pulses tunable in the infrared have been obtained through intracavity vibrational and rotational stimulated Raman scattering of a 20 millijoule alexandrite laser.

Study of Instabilities by Intracavity Nearly- Degenerate Four -Wave MixingRobert FreyLaboratoire d'Optique Quantique du C.N.R.S., Ecole Polytechnique91128 Palaiseau cedex, Franceand Ecole Nationale Superieure des Telecommunications (groupe Optique des materiaux),46 rue Barrault, 75634 Paris cedex 13, FranceHisao NakajimaEcole Nationale Superieure des Telecommunications (groupe Optique des materiaux)46 rue Barrault, 75634 Paris cedex 13, FranceNitin C. KothariLaboratoire d'Optique Quantique du C.N.R.S., Ecole Polytechnique91128 Palaiseau cedex, FranceAbstractIntracavity nearly- degenerate four -wave mixing is used to study instabilities occurringin Fabry -Perot laser cavities operating above or below threshold. Two -level theoretical cal-culations and experimental results obtained with semiconductor lasers are reported.1. IntroductionLaser instabilities are generally studied theoretically and experimentally in the caseof ring lasers with only one propagation direction. Such a setup is used in order to avoidproblems arising from spatial hole burning due to standing wave effects. Nevertheless, thecase of Fabry -Perot cavities is particularly interesting since it includes most lasers andbistable devices.This paper demonstrates that instability studies are possible with such Fabry -Perot lasercavities by means of a spectroscopic technique based on nearly degenerate four -wave mixing(NDFWM)1. The intracavity NDFWM technique may be performed on axis with the laser operatingeither above or below threshold. In the mixing process schematized in Fig.1, the pump wavesof frequency w are generated from the laser action itself or by amplification of an externalpump signal if the laser is below threshold. The conjugate beam of frequency w +6w is then obtained when a probe beam (w -6w) is sent through the cavity collinearly with the pump waves.2. Study of relaxation resonance frequency of lasers by NDFWMThis study has been performed theoritically with a laser medium modeled as an amplifyingtwo -level system and experimentally when using a GaAlAs semiconductor laser as the nonlinearFabry -Perot laser cavity.Calculations are performed by analytically solving the six coupled nonlinear propagationequations for the forward and backward pump (w), probe (w -6w) and conjugate (w +6w) wavespresent inside the laser cavity 2. Such equations would normally be difficult to solvebecause boundary conditions at z =0 and z =L are interconnected in such a Fabry -Perot cavity.Nevertheless, if the problem is restricted to a laser not operating far above threshold,that is, to weak saturation of the laser transition, the third order nonlinear polarizationis sufficient and a perturbative technique may be used to solved these propagation equa-tions. On the other hand our calculations take into account the standing wave nature of thelaser and the usual mean -field approximation is not required here.Fig.2 shows the calculated conjugate reflectivity RT plotted versus the normalized detu-ning 6 = 6w [Ti T'2 Ih (1)/It]1/2. In this expression T1 is the population relaxation timeof the amplifying two level systems

Optical logic functions can be obtained through nearly-degenerate four-wave mixing in laser diodes operating above as below threshold. In this nonlinear mixing process the pump frequency w is given either by laser oscillation or by amplification of an external pump signal. The conjugate frequency w + δw is then obtained by intracavity nearly-degenerate four-wave mixing when a probe beam of frequency w - δw is injected through the laser diode colinearly with the pump beam. Several examples using this technique are discussed including high contrast bistable memory, AND, OR, and INV gates.

High efficiency pulse compression using Raman induced cavity dumping has been studied theoretically and experimentally. Through stimulated Raman scattering the electromagnetic energy at a primary frequency is down-converted and extracted from a storage cavity containing the Raman medium. Energy storage may be achieved either at the laser frequency by using a laser medium inside the storage cavity, or performed at a new frequency obtained through an intracavity nonlinear process. The storage cavity may be dumped passively through stimulated Raman scattering either in an oscillator or in an amplifier. All these cases have been studied by using a ruby laser as the pump source and compressed hydrogen as the Raman scatter. Results differ slightly accordingly to the technique used, but pulse shortenings higher than 10 and quantum efficiencies higher than 80 % were obtained. This method could also be used with large power lasers of any wavelength from the ultraviolet to the farinfrared spectral region.

Experiments using intracavity nearly degenerate four-wave mixing in GaAlAs semiconductor laser oscillators and resonant-type amplifiers suggest that the resonance-relaxation process can be simply interpreted in terms of the dynamic Stark effect for a two-level system. This new interpretation is confirmed by a theoretical development demonstrating that lasers and resonant-type amplifiers can actually be represented well by an equivalent two-level system that takes into account both the semiconductor medium and cavity constants. Such an analysis can be useful for the study of higher-order instabilities.

On-axis intracavity nearly degenerate four-wave mixing performed inside a laser composed of inverted two-level systems is studied theoretically using analytical solutions for the propagation equations obtained in the case in which the undepleted pump laser is operating near threshold. Reflectivities up to 103–106 are predicted, together with bandwidths that make such a setup usable for practical applications. The influence of the ac Stark effect and cavity mistuning on the reflectivity is also considered.

High-efficiency pulse compression has been obtained by using an intracavity Raman oscillator. The energy of a primary laser stored in its high-Q cavity is extracted at the Stokes frequency by means of a Stokes laser having a high Raman gain and a low-Q cavity. This technique, using hydrogen gas as the Raman medium, permits shortening of the pulse duration of a ruby laser by a factor of 6.7 with 87% effective quantum efficiency. It would be especially useful with low-gain (alexandrite) and with short-storage-lifetime lasers.