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Physical Review A

Bichromatic emission in a ring dye laser

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

Published Aug 1, 1987• 9 citations
Publisher

Abstract

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.

DOI
10.1103/physreva.36.1759

Related papers

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

N. M. Lawandy

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.

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We present the results of an experimental study of phase locking counterrotating modes in a Rhodamine-6G continuous-wave broadband ring dye laser. Results for the measured mutual coherence of the counterrotating fields are presented for three different coupling geometries: namely, coupling by using an intracavity retroreflector, a single extracavity retroreflector placed in one of the output beams,and extracavity retroreflectors placed in each of the two output beams. We find that the highest degree of locking is obtained for the case of the intracavity retroreflector and leads to counterrotating outputswith a measured mutual coherence of unity.

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Dynamics and instabilities in homogeneously broadened lasers

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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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Emission spectra of concentrated (~10 18 –10 19 cm –3 ) ethanol solutions of Rhodamine C excited by high-power (~10 25 –10 26 cm –2 s –1 ) laser radiation were measured. The emission spectrum consists of two narrow bands (with half-widths of ~200–300 cm –1 ). The long-wavelength band was interpreted as cooperative spontaneous emission, and the short-wavelength band was assigned to the amplified spontaneous emission. The ratio of their intensities depends on the dye concentration and the pump power density. The ratio of band intensities is assumed to be determined by the dephasing rate of excited molecules responsible for cooperative spontaneous emission.

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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.

Soviet Journal of Quantum Electronics•Feb 28, 1978•0 citations
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.
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 present the results of an experimental study of phase locking counterrotating modes in a Rhodamine-6G continuous-wave broadband ring dye laser. Results for the measured mutual coherence of the counterrotating fields are presented for three different coupling geometries: namely, coupling by using an intracavity retroreflector, a single extracavity retroreflector placed in one of the output beams,and extracavity retroreflectors placed in each of the two output beams. We find that the highest degree of locking is obtained for the case of the intracavity retroreflector and leads to counterrotating outputswith a measured mutual coherence of unity.
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.
Emission spectra of concentrated (~10 18 –10 19 cm –3 ) ethanol solutions of Rhodamine C excited by high-power (~10 25 –10 26 cm –2 s –1 ) laser radiation were measured. The emission spectrum consists of two narrow bands (with half-widths of ~200–300 cm –1 ). The long-wavelength band was interpreted as cooperative spontaneous emission, and the short-wavelength band was assigned to the amplified spontaneous emission. The ratio of their intensities depends on the dye concentration and the pump power density. The ratio of band intensities is assumed to be determined by the dephasing rate of excited molecules responsible for cooperative spontaneous emission.
We have studied spectra and angular distribution of emission in Fabry–Perot cavities formed by two silver mirrors separated by a layer of poly (methyl methacrylate) polymer doped with rhodamine 6G (R6G) dye in low ( 20 g / l ) and high ( 200 g / l ) concentrations. The frequency of emission radiated to a cavity mode was larger at large outcoupling angles—the “rainbow” effect. At the same time, the angle of the strongest emission was also determined by the cavity size: the larger the cavity, the larger the angle. The angular distribution of emission is commonly dominated by two symmetrical lobes (located at the intersection of the three-dimensional emission cone with a horizontal plane) pointing to the left and to the right of the normal to the sample. Despite the strong Stokes shift in R6G dye, the branch of the cavity dispersion curve obtained in the emission experiment is positioned above the one obtained in the reflection (extinction) experiment. Some dye molecules are poorly coupled to cavity modes. Their emission has very broad angular distribution with the maximum at θ = 0 ∘ . The signatures of strong cavity–exciton coupling were observed at high dye concentration ( 200 g / l ) but not at low concentration ( 20 g / l ). The evidence of the effect of strong coupling on emission is exemplified by a strong difference in the angular distribution of emission in two almost identical cavities, one with and another without strong coupling. Most importantly, we have demonstrated the possibility to control the ground state concentration, the coupling strength, and the dye emission spectra with Q-switched laser pulses.
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.