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Optics Letters

Observation of Raman-shifted oscillation near the sodium D lines

Prem Kumar, Jeffrey H. Shapiro

Published May 1, 1985• 58 citations
Publisher

Abstract

We have observed oscillation in the wings of the Doppler-broadened sodium D lines when they are pumped by a cw dye laser and enclosed in an optical cavity. The oscillation is blue (red) detuned from the pump laser by the ground-state hyperfine splitting of sodium when the pump-laser frequency is in the blue (red) wing. The gain mechanism is explained on the basis of optical pumping and stimulated Raman scattering.

DOI
10.1364/ol.10.000226

Related papers

Frequency correlated laser beam generation in sodium vapor: sodium-density and pump-intensity dependence

Prem Kumar, Bernard Matthew Poelker

When sodium vapor is irradiated with a single-frequency dye laser (pump) tuned in the vicinity of either of the Doppler-broadened D lines and enclosed in an optical cavity, Raman shifted oscillation builds up, which is blue shifted for a blue-detuned pump and red shifted for a red-detuned pump by 1.772 GHz (sodium ground-state hyperfine splitting).1 The gain mechanism responsible for this Raman-laser action can be understood by modeling sodium as a three-level atom. The Raman laser frequency is highly correlated with that of the pump as demonstrated earlier by observing a beat frequency bandwidth between the two lasers of as low as 17 kHz.2 (The pump had rms frequency fluctuation of the order of 10 MHz.) For spectroscopic applications, for example, frequency correlated laser beams are commonly generated using acoustooptic techniques which are difficult to implement beyond the gigahertz region. The Raman laser technique is extendable, in principle, even to the millimeter range. Here we present measurements of the sodium-density and pump-intensity dependence of the Raman-laser output and compare the results with those predicted by the three-level-atom model.

Annual Meeting Optical Society of America•Jan 1, 1988•0 citations

Diode-laser pumped Raman-shifted oscillation in cesium vapor

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We report observing Raman-shifted oscillation within a ring cavity containing cesium vapor and pumped with the output of a single-frequency diode laser tuned near the D2 line. The oscillation is shifted from the diode-laser pump frequency by ≃9 GHz, the hyperfine splitting of the 6S1/2 ground state of cesium. Many different transverse modes of oscillation are observed for slight variations in the cavity alignment. In addition, the oscillation is observed to turn on and off at 60 Hz as a result of the pump-frequency fluctuations associated with the line noise on the diode-laser drive current. The pump-frequency fluctuations (≃10 MHz) are small compared with the free spectral range (175 MHz) of the ring cavity. These characteristics indicate that the Raman oscillation in cesium vapor is narrow-band, similar to the behavior observed in sodium vapor.1–3 As little as 30 mW of pump power is required for oscillation when highly reflective cavity optics are used. We have obtained 0.5 mW of Raman-shifted output with an appropriate output coupler at 65 mW of pump power.

Annual Meeting Optical Society of America•Jan 1, 1992•0 citations

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Sodium Raman laser: direct measurements of the narrow-band Raman gain

M. Poelker, Prem Kumar

Using a sodium Raman laser that is pumped by a single-frequency cw dye laser, we have measured the narrow-band Raman gain that exists in the vicinity of the sodium D(1) line. Large gains (>10 cm(-1)) are measured at moderate pump intensities and sodium densities. The high gain allows us to detect directly a 1.772-GHz beat on the pump beam after it makes only a single pass through the sodium cell. By scanning the frequency of the sodium Raman laser while keeping the pump intensity and frequency constant, we are able to map out the Raman gain profile. The narrowness of the Raman gain is consistent with the narrow beat signal between the Raman-laser beam and the pump beam that was reported earlier [Opt. Lett. 16, 1853 (1991)].

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Laser-based probes of chemically induced Raman pumping

David R. Grantier, James L. Gole

The highly selective Na3 + Br reaction creates a continuous electronic population inversion on Na2 transitions which demonstrates optical gain through stimulated emission in regions close to 527, 492, and 460 nm ((alpha) equals 8 X 10-3 cm-1 for an individual rotational level at approximately 527 nm). With a focus to increasing amplifier gain length and amplifying medium concentration (conversion to oscillator), we extend these initial studies employing the intersection of sodium and bromine flows formed from slit source expansions to create an extended reaction-amplification zone. Initial results with this extended reaction zone provide the first example of chemically induced Raman pumping. Unique Raman signals are induced by and correlate with emission from the NaD-line components (D1, D2) formed in the chemical reaction zone primarily as a result of the Na2 + Br yields Na* (3P) + NaBr reaction. The NaD-line emitters interact with cooled sodium dimers in a resonance Raman scattering process, for which computer simulation of the experimentally observed spectra predict an unusually large scattering linewidth close to 4 cm-1. We describe initial laser based studies on a pure sodium expansion to probe the mechanism of the unusually strong Raman scattering and to understand the origin of the large scattering linewidth. These experiments demonstrate that the Raman process can be induced only upon excitation of the NaD-line components, the Raman scattering being insufficient or nonexistent for wavelength shifts (Delta) (lambda) > 1 nm from the D lines. The scattering linewidth for the reactive process is not readily correlated with the line-broadening of the NaD-line and may result from the nature of the Na- Na2 interaction in the reactive environment. Initial double pass measurements indicate the possibility of optical gain associated with the Raman process.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Mar 29, 1996•2 citations

Strong amplification of sidebands in self-focused laser beams in an atomic vapor

A. C. Tam

A cw dye-laser beam tuned to the high-frequency wing of the Na ${D}_{2}$ line (at 2-6 GHz from the center of the ${D}_{2}$ line) is focused into a Na vapor, forming a self-focused laser filament. The incident laser beam, which is mainly single frequency, contains very weak sidebands at about \ifmmode\pm\else\textpm\fi{} 1 GHz from the main frequency and of intensity \ensuremath{\sim} ${10}^{\ensuremath{-}3}$ of the main frequency. Such sidebands are found to be strongly amplified by the vapor. Amplification factors in excess of 100 have been observed at suitable Na density, laser power, and detuning. Such strong sideband amplification, previously unknown, is explained as an off-resonant stimulated Raman scattering process.

Physical Review A•May 1, 1979•62 citations
We have observed oscillation in the wings of the Doppler-broadened sodium D lines when they are pumped by a cw dye laser and enclosed in an optical cavity. The oscillation is blue (red) detuned from the pump laser by the ground-state hyperfine splitting of sodium when the pump-laser frequency is in the blue (red) wing. The gain mechanism is explained on the basis of optical pumping and stimulated Raman scattering.
When sodium vapor is irradiated with a single-frequency dye laser (pump) tuned in the vicinity of either of the Doppler-broadened D lines and enclosed in an optical cavity, Raman shifted oscillation builds up, which is blue shifted for a blue-detuned pump and red shifted for a red-detuned pump by 1.772 GHz (sodium ground-state hyperfine splitting).1 The gain mechanism responsible for this Raman-laser action can be understood by modeling sodium as a three-level atom. The Raman laser frequency is highly correlated with that of the pump as demonstrated earlier by observing a beat frequency bandwidth between the two lasers of as low as 17 kHz.2 (The pump had rms frequency fluctuation of the order of 10 MHz.) For spectroscopic applications, for example, frequency correlated laser beams are commonly generated using acoustooptic techniques which are difficult to implement beyond the gigahertz region. The Raman laser technique is extendable, in principle, even to the millimeter range. Here we present measurements of the sodium-density and pump-intensity dependence of the Raman-laser output and compare the results with those predicted by the three-level-atom model.
We report observing Raman-shifted oscillation within a ring cavity containing cesium vapor and pumped with the output of a single-frequency diode laser tuned near the D2 line. The oscillation is shifted from the diode-laser pump frequency by ≃9 GHz, the hyperfine splitting of the 6S1/2 ground state of cesium. Many different transverse modes of oscillation are observed for slight variations in the cavity alignment. In addition, the oscillation is observed to turn on and off at 60 Hz as a result of the pump-frequency fluctuations associated with the line noise on the diode-laser drive current. The pump-frequency fluctuations (≃10 MHz) are small compared with the free spectral range (175 MHz) of the ring cavity. These characteristics indicate that the Raman oscillation in cesium vapor is narrow-band, similar to the behavior observed in sodium vapor.1–3 As little as 30 mW of pump power is required for oscillation when highly reflective cavity optics are used. We have obtained 0.5 mW of Raman-shifted output with an appropriate output coupler at 65 mW of pump power.
Generation of frequency correlated laser beams is of importance in various applications, in particular, for extending the frequency of the laser Raman microwave clock1 into the millimeter region where acoustooptic methods are not available. We propose and demonstrate an all-optical technique for such a purpose. The technique is based on the recently observed Raman-shifted oscillation2 that occurs when a three-level atomic system of Λ type is optically pumped and placed in a ring cavity. Our initial experiments are performed in sodium vapor pumped by a cw ring dye laser. Raman-shifted oscillation, detuned from the pump laser by 1.772 GHz which is the ground state hyperfine splitting of sodium, occurs in the wings of the Doppler broadened D1 line. This Raman-shifted oscillation is demonstrated to be highly frequency correlated with the pumping laser when the two are heterodyned on a fast photodetector. In our experiments the heterodyne beat signal at 1.772 GHz had a linewidth as low as 17 kHz, whereas the pumping laser has a rms frequency fluctuation of 300 kHz. The beat signal stays narrowband when the pumping laser is unlocked from the reference cavity increasing its rms frequency fluctation to ~10MHz.
Using a sodium Raman laser that is pumped by a single-frequency cw dye laser, we have measured the narrow-band Raman gain that exists in the vicinity of the sodium D(1) line. Large gains (>10 cm(-1)) are measured at moderate pump intensities and sodium densities. The high gain allows us to detect directly a 1.772-GHz beat on the pump beam after it makes only a single pass through the sodium cell. By scanning the frequency of the sodium Raman laser while keeping the pump intensity and frequency constant, we are able to map out the Raman gain profile. The narrowness of the Raman gain is consistent with the narrow beat signal between the Raman-laser beam and the pump beam that was reported earlier [Opt. Lett. 16, 1853 (1991)].
The highly selective Na3 + Br reaction creates a continuous electronic population inversion on Na2 transitions which demonstrates optical gain through stimulated emission in regions close to 527, 492, and 460 nm ((alpha) equals 8 X 10-3 cm-1 for an individual rotational level at approximately 527 nm). With a focus to increasing amplifier gain length and amplifying medium concentration (conversion to oscillator), we extend these initial studies employing the intersection of sodium and bromine flows formed from slit source expansions to create an extended reaction-amplification zone. Initial results with this extended reaction zone provide the first example of chemically induced Raman pumping. Unique Raman signals are induced by and correlate with emission from the NaD-line components (D1, D2) formed in the chemical reaction zone primarily as a result of the Na2 + Br yields Na* (3P) + NaBr reaction. The NaD-line emitters interact with cooled sodium dimers in a resonance Raman scattering process, for which computer simulation of the experimentally observed spectra predict an unusually large scattering linewidth close to 4 cm-1. We describe initial laser based studies on a pure sodium expansion to probe the mechanism of the unusually strong Raman scattering and to understand the origin of the large scattering linewidth. These experiments demonstrate that the Raman process can be induced only upon excitation of the NaD-line components, the Raman scattering being insufficient or nonexistent for wavelength shifts (Delta) (lambda) > 1 nm from the D lines. The scattering linewidth for the reactive process is not readily correlated with the line-broadening of the NaD-line and may result from the nature of the Na- Na2 interaction in the reactive environment. Initial double pass measurements indicate the possibility of optical gain associated with the Raman process.
A cw dye-laser beam tuned to the high-frequency wing of the Na D2{D}_{2}D2​ line (at 2-6 GHz from the center of the D2{D}_{2}D2​ line) is focused into a Na vapor, forming a self-focused laser filament. The incident laser beam, which is mainly single frequency, contains very weak sidebands at about \ifmmode\pm\else\textpm\fi{} 1 GHz from the main frequency and of intensity \ensuremath{\sim} ${10}^{\ensuremath{-}3}$ of the main frequency. Such sidebands are found to be strongly amplified by the vapor. Amplification factors in excess of 100 have been observed at suitable Na density, laser power, and detuning. Such strong sideband amplification, previously unknown, is explained as an off-resonant stimulated Raman scattering process.