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Physical Review A

Bidirectional ring laser: Stability analysis and time-dependent solutions

H. Zeghlache, Paul Mandel, N. B. Abraham, Lois M. Hoffer, Gian Luca Lippi, T. Mello

Published Jan 1, 1988• 90 citations
Publisher

Abstract

We provide a comprehensive analysis of the standard model of the bidirectional ring laser in which only one mode can be supported in each direction and in the limit that the polarization can be eliminated adiabatically. The interaction between the two counterpropagating modes can be derived and it is most naturally viewed as a coupling between them via scattering from a spatial grating formed in the population inversion. If the grating is a sufficiently small modulation of the spatial average of the population inversion, it can be approximated by a sinusoidal function. A systematic derivation of the model with only a sinusoidal grating for the homogeneously broadened case is presented that reveals and corrects errors in several previously published analyses. The stability of the steady-state solution is analyzed. The bidirectional steady-state solution is unstable and the unidirectional steady-state solutions may be stable or unstable depending on the parameters. The well-established result of bistability between the two modes when the cavity is tuned to resonance is recovered, a result that persists, in part, even when the losses between the two modes are different.With detuning, the unidirectional steady-state solutions can be destabilized, creating regions in the parameter space where only time-dependent solutions are found. For parameters characteristic of solid-state or molecular gas lasers, the instability can occur for very small detunings and even very close to the lasing threshold. Asymptotic limits of the instability boundaries for these parameters are presented. Additional results are derived formally for inhomogeneous broadening with a Lorentzian line shape and for arbitrary inhomogeneous linewidths. Explicit analytic results are presented in the limits of very small and very large inhomogeneous linewidths compared with the homogeneous linewidth. Time-dependent solutions in the homogeneously broadened case for relaxation rates appropriate to ${\mathrm{CO}}_{2}$ lasers show that there are broad regions in the parameter space of gain and detuning for which the behavior is dynamically chaotic in the form of nearly ``square-wave'' alternation between the counterpropagating modes of the laser with irregular switching times. In other regions of that parameter space we find more irregular pulsations and pulse alternations. Regions of periodic pulsations also have been found.

DOI
10.1103/physreva.37.470

Related papers

Phase and Frequency Dynamics in a Bidirectional Ring Laser

N. B. Abraham, Lois M. Hoffer, Gian Luca Lippi

Homogeneously broadened bidirectional ring lasers show alternation of the lasing direction induced dynamically by a long-lived population grating and slight detuning of the laser cavity from the atomic resonance1. We show that the mode switching is accompanied by abrupt jumps by pi in the total relative phase of the system2. Our analysis reveals that the carrier frequencies of the two modes are not equal even though the two unidirectional steady state solutions have the same frequency2. When one mode dominates and the other is suppressed, the dominant mode has the steady state frequency. However, a mode growing in strength has a frequency closer to the atomic resonance while a mode falling in strength has a frequency further from the atomic resonance. The dynamically induced mode-pulling and mode-pushing can be as much as 25 % of the steady state frequency detuning. The shifting frequencies of the modes indicate that the standing wave interference pattern rotates in the laser ring cavity, alternately moving clockwise and counterclockwise with nearly equal and constant speeds. The longitudinal spatial hole-burning pattern consequently also rotates in the ring tending to wash out the population grating and keeping it from developing an amplitude of much more than one percent of the spatially averaged population inversion.

Topical Meeting on Optical Bistability (OB)•Jan 1, 1988•0 citations

Time-dependent behavior of a unidirectional ring laser within homogeneous broadening

Donna Kay Bandy, L. A. Lugiato, N. B. Abraham +1 more

We solve numerically the time-dependent equations of motion for an inhomogeneously broadened single-mode ring laser. As expected from the linear stability analysis, pulsations develop in the output of the laser for appropriate values of the gain parameter. Under resonant conditions, the tendency is for the system to slip from a periodic regime into irregular oscillations; out of resonance, however, periodic oscillations and period-doubling bifurcations are more typical over a large range of gain values. We find that, as the ratio of the population-to-polarization decay rates varies from a value of two (radiative limit) to smaller values, the periodic oscillations turn into a train of well-separated pulses whose peak intensity scales approximately as the square of the atomic density.

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Semiclassical analysis of a detuned ring laser with a saturable absorber: New results for the steady states

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This paper presents new results for the steady states of a detuned ring laser with a saturable absorber. We employ a semiclassical model which assumes homogeneously broadened two-level atoms. We proceed by solving the Maxwell-Bloch equations for the longitudinal dependence of the steady states of this system, and then simplify our solution by use of the uniform-field approximation. We present uniform-field results for squared electric field versus operating frequency, and for each of these versus cavity tuning and laser excitation. Various cavity linewidths and both resonant and nonresonant amplifier and absorber line-center frequencies are considered. The most notable finding is that cavity detuning breaks the degeneracies found in the steady-state solutions of the fully tuned case. This leads to the prediction that an actual system will bifurcate from the zero-intensity solution to a steady-state solution as laser excitation increases from zero, rather than to the small-amplitude pulsations found for the model with exactly resonant tuning of the cavity and the media line centers. Other phenomena suggested by the steady-state results include tuning-dependent hysteresis and bistability, and instability in both intensity and frequency due to the appearance of one or more new steady-state solutions as tuning is varied. These effects of detuning are being tested by a linearized stability analysis whose results will be reported separately.

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Strong-signal laser operation. II. Specific cases

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The multimode strong-signal theory of the preceding paper is applied to a number of two- and three-mode cases. A two-mode stability analysis yields strong-signal counterparts to the third-order coupling parameter. Two-mode homogeneous-broadened operation leads to the discussion of population inversion gratings and associated Bragg scattering. Symmetry properties of the equations for the bidirectional ring are examined. Results for Doppler-broadened two-mode special cases and the three-mode locked unidirectional-ring operation are presented. The strong-signal results are compared to those of the third-order and rate-equation-approximation theories. For the bidirectional ring the historical third-order domain of relative excitation from 1.0 to 1.2 is divided into a valid third-order region and a less accurate region. The condition of bistable operation vs monostable operation is seen to be dependent on the relative excitation and the amount of homogeneous broadening. Two types of bistable operation are seen to exist, one where one mode is completely suppressed and another where both modes may have nonzero intensities.

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Properties of a Lorentz-broadened single-mode unidirectional ring laser

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We study some properties of a single-mode unidirectional ring laser characterized by a Lorentzian inhomogeneous broadening. The emphasis is on the derivation of analytic results. First we determine the various classes of stationary solutions and demonstrate the existence of low-intensity and high-intensity optical bistability. Both types of optical bistability require a finite detuning and inhomogeneous broadening. Next we study the linear stability of the steady solutions and determine the conditions for the occurrence of a Casperson instability in various limits but on resonance.

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Analytic self-pulsing solutions and their instabilities in a homogeneously broadened ring laser

Hong Fu

Analytical traveling-wave self-pulsing solutions of a homogeneously broadened ring laser are presented in the limit that the dipole relaxation rate is much greater than the atomic inversion relaxation rate. The phase velocity v(\ensuremath{\Lambda}) as a function of the normalized pump \ensuremath{\Lambda} is given explicitly. This function has a simple relation with the upper boundary ${\ensuremath{\alpha}}_{\mathrm{max}(\mathrm{\ensuremath{\Lambda}}}$) of the Risken-Nummedal-Graham-Haken (RNGH) instability domain in the (\ensuremath{\alpha},\ensuremath{\Lambda}) plane, where \ensuremath{\alpha} is the wave vector of the perturbations. The self-pulsing may appear in different ways, depending on how the stationary solution becomes unstable. If the instability of the stationary solution is caused by an unstable mode touching upon the upper boundary of the RNGH-instability domain in the (\ensuremath{\alpha},\ensuremath{\Lambda}) plane, the self-pulsing is supercritical; if the unstable mode lies on the lower boundary, a subcritical self-pulsing arises, and the system is bistable. This rule provides new signatures of the self-pulsing phenomena and will be helpful to experimental identification of the self-pulsing arising from the RNGH instability. The linear stability analysis reveals two kinds of instabilities for these self-pulsing solutions. One kind of instability is rooted in the RNGH instability of the stationary solution and may occur even when the amplitude of the self-pulsing solution approaches zero. The other kind of instability occurs when the oscillating amplitude of the self-pulsing solution becomes large. Above this large-amplitude instability threshold no traveling-wave self-pulsing can be stable any longer. The results for the corresponding Lorenz model are also presented.

Physical Review A•Aug 1, 1989•11 citations
We provide a comprehensive analysis of the standard model of the bidirectional ring laser in which only one mode can be supported in each direction and in the limit that the polarization can be eliminated adiabatically. The interaction between the two counterpropagating modes can be derived and it is most naturally viewed as a coupling between them via scattering from a spatial grating formed in the population inversion. If the grating is a sufficiently small modulation of the spatial average of the population inversion, it can be approximated by a sinusoidal function. A systematic derivation of the model with only a sinusoidal grating for the homogeneously broadened case is presented that reveals and corrects errors in several previously published analyses. The stability of the steady-state solution is analyzed. The bidirectional steady-state solution is unstable and the unidirectional steady-state solutions may be stable or unstable depending on the parameters. The well-established result of bistability between the two modes when the cavity is tuned to resonance is recovered, a result that persists, in part, even when the losses between the two modes are different.With detuning, the unidirectional steady-state solutions can be destabilized, creating regions in the parameter space where only time-dependent solutions are found. For parameters characteristic of solid-state or molecular gas lasers, the instability can occur for very small detunings and even very close to the lasing threshold. Asymptotic limits of the instability boundaries for these parameters are presented. Additional results are derived formally for inhomogeneous broadening with a Lorentzian line shape and for arbitrary inhomogeneous linewidths. Explicit analytic results are presented in the limits of very small and very large inhomogeneous linewidths compared with the homogeneous linewidth. Time-dependent solutions in the homogeneously broadened case for relaxation rates appropriate to CO2{\mathrm{CO}}_{2}CO2​ lasers show that there are broad regions in the parameter space of gain and detuning for which the behavior is dynamically chaotic in the form of nearly ``square-wave'' alternation between the counterpropagating modes of the laser with irregular switching times. In other regions of that parameter space we find more irregular pulsations and pulse alternations. Regions of periodic pulsations also have been found.
Homogeneously broadened bidirectional ring lasers show alternation of the lasing direction induced dynamically by a long-lived population grating and slight detuning of the laser cavity from the atomic resonance1. We show that the mode switching is accompanied by abrupt jumps by pi in the total relative phase of the system2. Our analysis reveals that the carrier frequencies of the two modes are not equal even though the two unidirectional steady state solutions have the same frequency2. When one mode dominates and the other is suppressed, the dominant mode has the steady state frequency. However, a mode growing in strength has a frequency closer to the atomic resonance while a mode falling in strength has a frequency further from the atomic resonance. The dynamically induced mode-pulling and mode-pushing can be as much as 25 % of the steady state frequency detuning. The shifting frequencies of the modes indicate that the standing wave interference pattern rotates in the laser ring cavity, alternately moving clockwise and counterclockwise with nearly equal and constant speeds. The longitudinal spatial hole-burning pattern consequently also rotates in the ring tending to wash out the population grating and keeping it from developing an amplitude of much more than one percent of the spatially averaged population inversion.
We solve numerically the time-dependent equations of motion for an inhomogeneously broadened single-mode ring laser. As expected from the linear stability analysis, pulsations develop in the output of the laser for appropriate values of the gain parameter. Under resonant conditions, the tendency is for the system to slip from a periodic regime into irregular oscillations; out of resonance, however, periodic oscillations and period-doubling bifurcations are more typical over a large range of gain values. We find that, as the ratio of the population-to-polarization decay rates varies from a value of two (radiative limit) to smaller values, the periodic oscillations turn into a train of well-separated pulses whose peak intensity scales approximately as the square of the atomic density.
This paper presents new results for the steady states of a detuned ring laser with a saturable absorber. We employ a semiclassical model which assumes homogeneously broadened two-level atoms. We proceed by solving the Maxwell-Bloch equations for the longitudinal dependence of the steady states of this system, and then simplify our solution by use of the uniform-field approximation. We present uniform-field results for squared electric field versus operating frequency, and for each of these versus cavity tuning and laser excitation. Various cavity linewidths and both resonant and nonresonant amplifier and absorber line-center frequencies are considered. The most notable finding is that cavity detuning breaks the degeneracies found in the steady-state solutions of the fully tuned case. This leads to the prediction that an actual system will bifurcate from the zero-intensity solution to a steady-state solution as laser excitation increases from zero, rather than to the small-amplitude pulsations found for the model with exactly resonant tuning of the cavity and the media line centers. Other phenomena suggested by the steady-state results include tuning-dependent hysteresis and bistability, and instability in both intensity and frequency due to the appearance of one or more new steady-state solutions as tuning is varied. These effects of detuning are being tested by a linearized stability analysis whose results will be reported separately.
The multimode strong-signal theory of the preceding paper is applied to a number of two- and three-mode cases. A two-mode stability analysis yields strong-signal counterparts to the third-order coupling parameter. Two-mode homogeneous-broadened operation leads to the discussion of population inversion gratings and associated Bragg scattering. Symmetry properties of the equations for the bidirectional ring are examined. Results for Doppler-broadened two-mode special cases and the three-mode locked unidirectional-ring operation are presented. The strong-signal results are compared to those of the third-order and rate-equation-approximation theories. For the bidirectional ring the historical third-order domain of relative excitation from 1.0 to 1.2 is divided into a valid third-order region and a less accurate region. The condition of bistable operation vs monostable operation is seen to be dependent on the relative excitation and the amount of homogeneous broadening. Two types of bistable operation are seen to exist, one where one mode is completely suppressed and another where both modes may have nonzero intensities.
We study some properties of a single-mode unidirectional ring laser characterized by a Lorentzian inhomogeneous broadening. The emphasis is on the derivation of analytic results. First we determine the various classes of stationary solutions and demonstrate the existence of low-intensity and high-intensity optical bistability. Both types of optical bistability require a finite detuning and inhomogeneous broadening. Next we study the linear stability of the steady solutions and determine the conditions for the occurrence of a Casperson instability in various limits but on resonance.
Analytical traveling-wave self-pulsing solutions of a homogeneously broadened ring laser are presented in the limit that the dipole relaxation rate is much greater than the atomic inversion relaxation rate. The phase velocity v(\ensuremath{\Lambda}) as a function of the normalized pump \ensuremath{\Lambda} is given explicitly. This function has a simple relation with the upper boundary ${\ensuremath{\alpha}}_{\mathrm{max}(\mathrm{\ensuremath{\Lambda}}}$) of the Risken-Nummedal-Graham-Haken (RNGH) instability domain in the (\ensuremath{\alpha},\ensuremath{\Lambda}) plane, where \ensuremath{\alpha} is the wave vector of the perturbations. The self-pulsing may appear in different ways, depending on how the stationary solution becomes unstable. If the instability of the stationary solution is caused by an unstable mode touching upon the upper boundary of the RNGH-instability domain in the (\ensuremath{\alpha},\ensuremath{\Lambda}) plane, the self-pulsing is supercritical; if the unstable mode lies on the lower boundary, a subcritical self-pulsing arises, and the system is bistable. This rule provides new signatures of the self-pulsing phenomena and will be helpful to experimental identification of the self-pulsing arising from the RNGH instability. The linear stability analysis reveals two kinds of instabilities for these self-pulsing solutions. One kind of instability is rooted in the RNGH instability of the stationary solution and may occur even when the amplitude of the self-pulsing solution approaches zero. The other kind of instability occurs when the oscillating amplitude of the self-pulsing solution becomes large. Above this large-amplitude instability threshold no traveling-wave self-pulsing can be stable any longer. The results for the corresponding Lorenz model are also presented.