Two-photon-pumped amplified spontaneous emission and cavity lasing of an organic dye HEASPS in PHEMA polymer

Two-photon-absorption (TPA)-induced upconverted amplified spontaneous emission (ASE) and cavity lasing of a styrylpyridinium dye: trans-4-[p-(N-hydroxyethyl-N-ethylamino)styryl]-N-methylpyridinium p-toluene sulfonate (abbreviated as HEASPS) in poly(2-hydroxyethyl methacrylate) (abbreviated as PHEMA) polymer were observed under a picosecond pump condition. The spectral and temporal behaviors of TPA-induced fluorescence, ASE and cavity lasing were studied. The cavity lasing with a total oscillation time of more than 200 ps was achieved when pumped with 1064-nm, 50-ps laser irradiation. The population inversion could persist for three times longer than the duration of the pump pulse. The gain coefficients of the dye-doped polymer at various wavelengths were calculated based on cavity lasing spectra and one-photon fluorescence spectra. PACS 78.20.Ek; 42.65.Ky; 42.65.Re; 78.47.+p     

Onset of Lasing in Small Devices: The Identification of the First Threshold through Autocorrelation Resonance

A simple technique for identifying the onset of coherent emission in mesoscale lasers, which makes use of a small‐amplitude modulation added to the pump, is introduced. The optimal modulation frequency is obtained from the radio‐frequency power spectrum of the unperturbed laser emission. The identification of the lasing onset rests on the appearance of a resonance in the experimentally measured zero‐order autocorrelation function (g⁽²⁾(0)) plotted as a function of the pump rate. Numerical proof is provided in support of the autocorrelation resonance. The intrinsic simplicity of this technique and its inherent compatibility with photon counting makes it an excellent tool for certifying the onset of laser emission independent of the laser cavity volume. Recently published measurements of g⁽²⁾(0), obtained in nanolasers, support the extension of this technique to nanoscale devices.     

NaK 22Σ+ → 11Σ+ band optically pumped laser near 1.02 μm

Optically pumped laser emission has been observed on the NaK 2(A)¹⁺ 1(X)¹⁺ electronic state transition. The emission occurs between 1.015 and 1.035 m when a sodium-potassium heat-pipe oven is pumped with 695–745 nm pulsed dye laser radiation. The laser emission occurs on many ro-vibrational transitions without the use of cavity mirrors. However, the addition of a simple cavity increases both the number of observed lasing transitions and the amplitude of the emission on each line. We report our results for the dependence of the emission intensity on pump laser power, oven temperature, and buffer gas pressure.     

原子在双腔场间的光子辐射

考虑单个二能级原子穿过两个空间分离的单模腔场,研究原子质心运动的动能、腔长和腔间距对原子的光子辐射率的影响.结果表明,在原子的动能较小时,光子辐射率在双腔系统中出现多共振峰结构并且这种共振峰的数目随腔间距的增大而增加,此时原子在第一个腔中的光子辐射率普遍大于在第二个腔中的;在原子的动能较大时,原子在第一个腔中的光子辐射率与第二个腔中的光子辐射率呈交替变化.该结果说明,可以通过控制原子的速度而对原子的光子辐射率进行调控. 关键词： 光子辐射率 单模腔场 二能级原子     

Vacuum-stimulated raman scattering based on adiabatic passage in a high-finesse optical cavity

We report on the first observation of stimulated Raman scattering from a Lambda-type three-level atom, where the stimulation is realized by the vacuum field of a high-finesse optical cavity. The scheme produces one intracavity photon by means of an adiabatic passage technique based on a counterintuitive interaction sequence between pump laser and cavity field. This photon leaves the cavity through the less-reflecting mirror. The emission rate shows a characteristic dependence on the cavity and pump detuning, and the observed spectra have a subnatural linewidth. The results are in excellent agreement with numerical simulations.     

Lasing on the resonance transition in sodium atoms under nonresonant optical excitation

Coherent emission on the 3P–3S resonance transition (D line) of nonresonantly excited sodium atoms in a buffer gas atmosphere is studied experimentally and theoretically. Both forward and backward coherent emission on the D lines is observed relative to the propagation direction of a pump beam whose frequency is blue-shifted from resonance. The divergence of the emitted radiation does not exceed that of the pump beam. The emission is due to the population inversion created on the “operating” transition when the pump is far detuned from resonance and the buffer gas pressure is sufficiently high. It is found that both emission intensity and the detuning range where this phenomenon is observed increase with the buffer gas pressure.     

Residual pump light as a probe of self-pulsing instability in an ytterbium-doped fiber laser

Self-pulsing instability in the ytterbium-doped fiber (YDF) laser is investigated with the pump-bypassed cavity configuration. The residual pump light acts as a probe of the intracavity dynamics, and the temporal behavior of the light shows correlations with the self-mode locking instability in the original cavity and the sustained self-pulsing instability in the modified cavity of the YDF laser. The results suggest that the interactions among stimulated emission, pump absorption and/or reabsorption could account for self-pulsing instability in the YDF laser. The pump-bypassed laser cavity configuration can be used to investigate the instabilities of various kinds of fiber lasers.     

High frequency fiber laser emission generated by pump spiking

A stable and short pulse train of ∼100 MHz repetition frequency was obtained from an erbium doped fiber laser excited by a “continuous” semiconductor laser and by using a linear cavity defined by a Bragg grating pair. The operation frequency of the fiber laser was greater (∼5-15 times) than the cavity round-trip frequency. Emission properties obtained from the erbium doped fiber laser were correlated with those taken from the pump laser, which presented a particular optical noise (very short pulses) added to the continuous emission. From the temporal and radio-frequency analysis of both systems, we conclude that the pump emission characteristics are the responsible of the fiber laser pulsed behaviour.     

Effect of pump power on the tuning range of a filterless erbium-doped fiber ring laser

In this paper, we establish the influence of pump power on the tuning characteristics of a filterless erbium-doped fiber laser, operating in the L band. Tunable action is achieved with the control of intra cavity loss. The explicit dependence of tunability on the average inversion levels is brought out. The shift in the lower limit of tuning range and the non-linear dependence of lasing wavelength on the intra cavity loss are analytically deduced using the gain spectra and experimentally interpreted using amplified spontaneous emission spectra. Continuous tunability is achieved with the careful control of pump power. PACS 42.55.Wb; 42.60.Da; 42.55.-f     

Laser induced lasing in CS2 vapor

When CS₂, contained in a tube at pressures ranging from 350 to 450 mTorr, was optically excited by a pulsed laser at a wavelength of 343.6 nm to the J=29, v=(0, 10, 0), R ³ B ₂ state (i.e., the =0 component of the a ³ A ₂ state), six coherent emissions were observed along the same axis from both ends of the tube. These emissions possess the characteristics of the pump laser, such as linewidth, pulse duration and polarization, but do not need a cavity to gain amplification. The emissions terminate on the high vibrational states of the ground electronic state. A time delay between the pump laser and the emissions was observed. The emission intensity depends non-linearly on the CS₂ pressure and exhibits a third order power dependence. A cooperative stimulated emission model is proposed to explain this phenomenon.     

Characteristics of Nd：GdVO4 Laser with Different Nd-Doping Concentrations

We report the properties of a compact diode-pumped continuous-wave Nd：GdV04 laser with a linear cavity and different Nd-doped laser crystals. In a 0.2at.% Nd-doped Nd：GdVO4 laser, 1.54 W output laser power is achieved at 912nm wavelength with a slope efficiency of 24.8% at an absorbed pump power of 9.4W. With 0.3at.% Nd-doping concentration, we can obtain the either single-wavelength emission at 1064nm or 912nm or the dual-wavelength emission at 1064nm and 912nm by controlling the incident pump power. From an incident pump power of 11.6 W, the 1064nm emission between ^4Fa/2 and ^4I11/2 is suppressed completely by the 912nm emission between ^4Fa/2 and ^4I9/2. We obtain 670 mW output of the 912nm single-wavelength laser emission with a slope efficiency of 5.5% by taking an incident pump power of 18.4 W. Using a Nd：GdV04 laser with 0.4at.% Nd-doping concentration, we obtain either the single-wavelength emission at 1064nm or the dual-wavelength emission at both 1064nm and 912nm by increasing the incident pump power. We observe a strong competition process in the dualavelength laser.     

Collective effects in the dynamics of driven atoms in a high-Q resonator

We study the quantum dynamics of N coherently driven two-level atoms coupled to an optical resonator. In the strong coupling regime the cavity field generated by atomic scattering interferes destructively with the pump on the atoms. This suppresses atomic excitation and even for strong driving fields prevents atomic saturation, while the stationary intracavity field amplitude is almost independent of the atom number. The magnitude of the interference effect depends on the detuning between laser and cavity field and on the relative atomic positions and is strongest for a wavelength spaced lattice of atoms placed at the antinodes of the cavity mode. In this case three dimensional intensity minima are created in the vicinity of each atom. In this regime spontaneous emission is suppressed and the dominant loss channel is cavity decay. Even for a cavity linewidth larger than the atomic natural width, one regains strong interference through the cooperative action of a sufficiently large number of atoms. These results give a new key to understand recent experiments on collective cavity cooling and may allow to implement fast tailored atom-atom interactions as well as nonperturbative particle detection with very small energy transfer.Received: 18 May 2004, Published online: 19 October 2004PACS: 32.80.Pj Optical cooling of atoms; trapping - 42.50.Pq Cavity quantum electrodynamics; micromasers - 42.50.Fx Cooperative phenomena in quantum optical systems     

Bipolariton laser emission from a GaAs microcavity

Biexciton emission properties were studied in a single GaAs quantum well semiconductor planar microcavity by photoluminescence measurements at low temperatures. At high pump intensity a bipolariton emission appears close to the lower polariton mode. This new mode appears when we detune the cavity resonance out of the lower polariton branch, showing a laser-like behavior. Very small linewidths were measured, lying below 110 μeV and 150 μeV for polariton and bipolariton emission respectively. The input/output power (I/O) measurements show that the bipolariton emission has a weaker coupling efficiency compared to previous results for polariton emission. Varying the pump laser polarization, we were able to show the selection rules for the biexciton particle creation in the quantum well. Simultaneous photoluminescence and near-field measurements show that the polariton and bipolariton emission are spectrally and spatially separated.     

Electromagnetically induced transparency of single Λ-type three-level atom in high-finesse optical cavity

We study the features of the electromagnetically induced transparency (EIT) in a single Λ-type three-level atom placed in a high finesse cavity under the action of a coupling laser and a probe laser. Our calculations show that three transparency windows appear when the pump strength is big enough. It can be explained by the residual pump in the cavity resulting mostly in the energy splitting. Level |3〉is split into four slightly different energy levels. An interference takes place between excitation pathways. Furthermore, it is also shown that the frequencies of the EIT windows can be tuned by changing the coupling field detuning Δ₂ and the reflection profile is very sensitive to the cavity field detuning Δ_c.     

Continuous-wave simultaneous dual-wavelength and power-ratio-tunable operation at 1064 and 1342 nm in an Nd:LuVO<Subscript>4</Subscript> laser

This study demonstrates continuous-wave simultaneous dual-wavelength emission at 1064 and 1342 nm in an Nd:LuVO₄ laser by using a T-type cavity configuration. The output powers indicating a function of pump power had two evolutions depending on the strength of the completion of two wavelength emissions. One is that the output power increased linearly with the pump power in weak competition, and the output power and slope efficiency of 1064 and 1342 nm were 1.17 W and 13%, and 0.213 W and 2.8%, respectively. The other is that the extracting-energy capabilities of two wavelength emissions were close, and the evolution was not linear and the variations demonstrated multiple stages depending on the pump power. Moreover, the ratio of output power, defined as the output power at 1064 nm divided by that at 1342 nm, is tuned from 0 to 5.5 by varying the 1064 nm cavity, and equal output powers of 1064 and 1342 nm can be obtained at each pump power.     

Improvement of the operation parameters for a Cr:LiSAF ultrashort-pulsed laser

The optimization of the pumping power that is focused on a gain medium inside an optical cavity is fundamental for increasing the efficiency of the power transferred inside a crystal, in this way increasing the output power of the laser. Nevertheless, in the case of pumping with a highly astigmatic laser diode, an undesirable form of the beam is focused on the cavity and the process to improve the cross section and sizes of the beam produce a notable reduction in the effective pump power ultimately focused in the crystal. The cavity design improvements for a Cr:LiSAF laser pumped with a 200 um × 1 um laser diode emission is presented for three different configurations, Z, V, and ring. The pump power is introduced in the cavity through a simple optical array, coupling more than 83% of the laser-diode power. The design requirements for the resonant cavity are reviewed in order to improve the coupling between the fundamental mode of the cavity and the cross-section form of the pumping beam. The stability limits of the cavities and Kerr sensitivity region are presented.     

Pulsed alkali pump light sources for Nd:YAG lasers

Pulsed arc discharges in alkali metal vapours are investigated for use as pump light sources for Nd:YAG lasers. Alkali lamps have a very high radiation efficiency and emit strong lines near the laser pump bands. These absorption bands are fitted by the emission spectrum of sodium and potassium lamps by changing the vapour pressure and input power. The spectral radiation distributions of the lamps are measured by a spectrograph with a gated OMA system. Ray tracing calculations for a laser cavity are used to evaluate the efficiency of the alkali radiation emission for Nd:YAG pumping. The results show that the excitation efficiency of the alkali lamps is twice as high as that of usually used rare gas lamps. For sodium resonance lines the side-on spectral radiance is calculated by a radiation transport model to estimate the pressure and the temperature profile. The results indicate that the alkali vapour lamps could be used as pump light sources with high efficiencies and low heat loading of the laser cavity.     

Narrow-linewidth, pump-enhanced singly-resonant parametric oscillator pumped at 532 nm

3 is demonstrated. The pump wave is provided by a frequency-doubled miniature Nd:YAG ring laser and is resonantly enhanced in the SRO cavity, resulting in an external threshold of 200 mW. Stable single-frequency emission in the 1000–1135 nm range has been obtained with 2 GHz continuous tunability and signal/idler linewidths <160 kHz. Received: 25 August 1997     

Interference effects between raman and parametric stimulated emission

The interaction between stimulated electronic Raman scattering and four wave parametric emission in potassium has been studied on the basis of common real states and emission channels. The modified intensity Stokes dependence and higher saturation pump intensity have been accounted for by the model developed. Two tunable pump waves are used to initiate the two steps, involving a dipole forbidden 4S – 3D transition.     

Multiphonon Bundle Emission in a Strong-Coupling Cavity Optomechanical System

Nonclassical effects in mesoscopic systems have attracted much attention recently. In this paper, it is shown that multiphonon bundle emission can be observed in a strong-coupling cavity optomechanical system. Theoretical analysis shows that when the driving field is adjusted to nth-order sideband excitation, the coupling between the cavity mode and the vibrational mode leads to super-Rabi oscillations, and finally results in an n-phonon bundles emission. Based on the current technology, this process can work in a wide range of parameters. Numerical simulation confirms the validity of the derivation. It is thought that this physical mechanism broadens the applications of cavity optomechanical system in realm of quantum phononics, such as in quantum metrology and phonon laser.