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International Laser Science Conference

Bichromatic emission in a homogeneously broadened ring dye laser: evidence of a new mode structure hierarchy

N. M. Lawandy

Published Jan 1, 1986• 1 citation
Publisher

Abstract

We present experimental measurements on a high-Q rhodamine 6G ring dye laser which was found to exhibit bichromatic emission with splittings of the order of 15–80 Å while operating in the range of 2–6 times above threshold in the bidirectional mode. Experiments were performed with the insertion of a low loss Faraday isolator (loss < 1%) in order to examine the effects of saturation gratings on the bichromatic emission. The results showed that even though the intracavity power went up, owing to the elimination of spatial hole burning, the bichromatic emission was completely eliminated in the operating range between 1 and 10 times above threshold. In addition the sidelight fluorescence of the jet was spectrally examined in order to search for sideband splittings similar to those found in Na atoms in a strong resonant field. No evidence of splittings or fluorescence shape change was found when the laser was 1–10 times above threshold. When a weak reflection from an intracavity element was allowed to make a single pass through the active part of the jet in a direction opposite to that allowed by the Faraday rotator, bichromatic emission was recovered at high pump powers (2–5 W). This is believed to be a consequence of a Bragg grating which appears when the weak beam is sent through the active medium. We describe the experiments and the results which we obtained, as well as offer a theory which consistently explains our observations and perhaps those of others.

DOI
10.1364/ils.1986.tuf3

Related papers

Bichromatic emission in a ring dye laser

N. M. Lawandy, Robert S. Afzal, W. S. Rabinovich

We have performed an experimental study of a high-Q Rhodamine 6G ring dye laser and have measured bichromatic emission with wavelength spacings as large as 110 A\r{} when the laser operated bidirectionally. The bichromatic emission vanished at all excitations when the laser was forced into unidirectional operation using a Faraday isolator. However, when a weak reflected beam was allowed to make a single pass in the direction opposite to that allowed by the Faraday device, bichromatic emission is recovered at the higher pump powers. The experiments show that no discontinuities occur in the intracavity power as a function of excitation and that the intracavity fields which are completely consistent with the measured thresholds are not capable of producing Rabi splittings larger than a few angstroms. In addition, we have observed no structure in the spontaneous emission spectrum of the dye when the bichromatic emission (80-A\r{} splitting) was present in the laser mode. We have been able to quantitatively fit the threshold and wavelengths of the bichromatic emission using a distributed feedback mode analysis with a cavity-mode-induced susceptibility grating.

Physical Review A•Aug 1, 1987•9 citations

Dynamics and instabilities in homogeneously broadened lasers

Karl W. Koch

Abstract : This thesis describes theoretical and experimental studies of a homogeneously broadened ring dye laser; particularly the two frequency instability in which a bichromatic field emerges from the laser above the instability threshold. The interaction of a bichromatic field with an isolated atomic resonance is examined. The time averaged inversion and the saturated gain exhibit structure in the form of a series of subharmonic resonances. The stability of a strong bichromatic laser field to the growth of a subharmonic probe field is examined. The gain of the subharmonic bichromatic probe field in the presence of the strong bichromatic laser field is calculated. The strong bichromatic field is stable to the growth of the subharmonic fields when the modulation frequency of the strong field coincides with the Rabi frequency of the lasing transition. The existence of chaos in a strongly driven nonlinear system is experimentally investigated in a multimode ring dye laser. A dye laser is pumped with a modulated pump source. The response of the dye laser to commensurate and incommensurate modulations is reported. For commensurate modulations, the dye laser responds in a periodic fashion and the rf spectrum of the dye is composed of a series of harmonics. For incommensurate modulations, the dye laser responds in a quasiperiodic fashion with a broadband rf spectrum.

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Amplitude-spectral asymmetry of stimulated emission from dye solutions

V. I. Bezrodnyi, N M Narovlyanskaya, Eugene A. Tikhonov

A report is given of a study of the amplitude-spectral asymmetry of the stimulated emission of superfluorescence from dye solutions pumped longitudinally by nanosecond laser pulses. This amplitude asymmetry is manifested by the difference between the powers of the forward and backward waves, and it is a function of the rate of pumping and of the optical density of the active medium. The asymmetry of stimulated emission from a ring laser is manifested by the appearance of a wave with a traveling-wave ratio of ~90 in the absence of any optical isolators. The spectral asymmetry of a ring laser is manifested by a difference between the spectra of strong and weak waves traveling in opposite directions. A quantitative analysis is made of the effects based on the solution of the transfer equations for radiation traveling in a nonlinearly absorbing active medium.

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Physical interpretation of bistable unidirectional ring-laser operation

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Bidirectional ring laser: Stability analysis and time-dependent solutions

H. Zeghlache, Paul Mandel, N. B. Abraham +3 more

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.

Physical Review A•Jan 1, 1988•90 citations

Instabilities, mode coexistence, and bistable behavior in a dye ring laser and an argon-ion laser at low excitation near threshold

Yongqing Li, Changsheng Wang, Yuzhu Wang

The factors affecting the dynamic instabilities of a cw dye laser operating near threshold are pumping fluctuation, spontaneous emission, nonlinear mode coupling, and spatial hole burning. Several experiments have found the surprising influence of these factors on the photon statistics,1 mode coexistence,2 bistable behavior,3 and sensitivity of intracavity laser spectroscopy4 in standing wave dye lasers.

•May 21, 1990•0 citations
We present experimental measurements on a high-Q rhodamine 6G ring dye laser which was found to exhibit bichromatic emission with splittings of the order of 15–80 Å while operating in the range of 2–6 times above threshold in the bidirectional mode. Experiments were performed with the insertion of a low loss Faraday isolator (loss < 1%) in order to examine the effects of saturation gratings on the bichromatic emission. The results showed that even though the intracavity power went up, owing to the elimination of spatial hole burning, the bichromatic emission was completely eliminated in the operating range between 1 and 10 times above threshold. In addition the sidelight fluorescence of the jet was spectrally examined in order to search for sideband splittings similar to those found in Na atoms in a strong resonant field. No evidence of splittings or fluorescence shape change was found when the laser was 1–10 times above threshold. When a weak reflection from an intracavity element was allowed to make a single pass through the active part of the jet in a direction opposite to that allowed by the Faraday rotator, bichromatic emission was recovered at high pump powers (2–5 W). This is believed to be a consequence of a Bragg grating which appears when the weak beam is sent through the active medium. We describe the experiments and the results which we obtained, as well as offer a theory which consistently explains our observations and perhaps those of others.
We have performed an experimental study of a high-Q Rhodamine 6G ring dye laser and have measured bichromatic emission with wavelength spacings as large as 110 A\r{} when the laser operated bidirectionally. The bichromatic emission vanished at all excitations when the laser was forced into unidirectional operation using a Faraday isolator. However, when a weak reflected beam was allowed to make a single pass in the direction opposite to that allowed by the Faraday device, bichromatic emission is recovered at the higher pump powers. The experiments show that no discontinuities occur in the intracavity power as a function of excitation and that the intracavity fields which are completely consistent with the measured thresholds are not capable of producing Rabi splittings larger than a few angstroms. In addition, we have observed no structure in the spontaneous emission spectrum of the dye when the bichromatic emission (80-A\r{} splitting) was present in the laser mode. We have been able to quantitatively fit the threshold and wavelengths of the bichromatic emission using a distributed feedback mode analysis with a cavity-mode-induced susceptibility grating.
Abstract : This thesis describes theoretical and experimental studies of a homogeneously broadened ring dye laser; particularly the two frequency instability in which a bichromatic field emerges from the laser above the instability threshold. The interaction of a bichromatic field with an isolated atomic resonance is examined. The time averaged inversion and the saturated gain exhibit structure in the form of a series of subharmonic resonances. The stability of a strong bichromatic laser field to the growth of a subharmonic probe field is examined. The gain of the subharmonic bichromatic probe field in the presence of the strong bichromatic laser field is calculated. The strong bichromatic field is stable to the growth of the subharmonic fields when the modulation frequency of the strong field coincides with the Rabi frequency of the lasing transition. The existence of chaos in a strongly driven nonlinear system is experimentally investigated in a multimode ring dye laser. A dye laser is pumped with a modulated pump source. The response of the dye laser to commensurate and incommensurate modulations is reported. For commensurate modulations, the dye laser responds in a periodic fashion and the rf spectrum of the dye is composed of a series of harmonics. For incommensurate modulations, the dye laser responds in a quasiperiodic fashion with a broadband rf spectrum.
A report is given of a study of the amplitude-spectral asymmetry of the stimulated emission of superfluorescence from dye solutions pumped longitudinally by nanosecond laser pulses. This amplitude asymmetry is manifested by the difference between the powers of the forward and backward waves, and it is a function of the rate of pumping and of the optical density of the active medium. The asymmetry of stimulated emission from a ring laser is manifested by the appearance of a wave with a traveling-wave ratio of ~90 in the absence of any optical isolators. The spectral asymmetry of a ring laser is manifested by a difference between the spectra of strong and weak waves traveling in opposite directions. A quantitative analysis is made of the effects based on the solution of the transfer equations for radiation traveling in a nonlinearly absorbing active medium.
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.