Two-photon Pumping Research Articles

Generation of squeezing in two-photon three-level media

We present a fully quantum-mechanical theory of nondegenerate four-wave mixing processes in three-level cascades with a two-photon pump. The results are applied to the generation of squeezed states of light. We find almost perfect squeezing for some strong pump intensities and tunings within the Rabi sidebands. We find good broadband squeezing for low pump intensities and tunings outside a small region around central tuning. Both cases avoid regions of significant spontaneous emission.

Dynamic stark effect in the 4p2p-3s2s transition of sodium by intense two-photon pumping

Dynamic Stark shift and splitting in the u.v. transition 4p-3s of sodium has been studied under two-photon pumping of the 5s state. The influence of pump detuning, laser power and sodium pressure have been measured and compared with the theoretical model for three-level system

Optical properties and formation of oxygen-perturbed F2 + color center in NaCl.

The optical properties of a recently discovered laser-active color center in oxygen-doped NaCl are reported. The color center is produced through a two-step photoaggregation process in additively colored crystals. Optical spectroscopy indicates that the point defect is a perturbed ${F}_{2}$${\mathrm{}}^{+}$ center. The center has very broad absorption and emission bands peaking at 1.09 and 1.55 \ensuremath{\mu}m, respectively, with a dipole moment oriented along the 〈110〉 directions of the crystal. The center population can be fully aligned along any 〈110〉 direction by using two-photon pumping. Ground- and excited-state absorption spectra compare well with the dielectrically embedded ${\mathrm{H}}_{2}$${\mathrm{}}^{+}$ model for the eight transitions observed. uv spectroscopy has identified the substitutional ${\mathrm{O}}^{2\mathrm{\ensuremath{-}}}$ ion as being the necessary impurity for the center formation. The proposed model for the color center is an ${\mathrm{O}}^{2\mathrm{\ensuremath{-}}}$-perturbed ${F}_{2}$${\mathrm{}}^{+}$ defect. The perturbing ${\mathrm{O}}^{2\mathrm{\ensuremath{-}}}$ ion serves both as a stable electron trap as well as a spatial trap for the ${F}_{2}$${\mathrm{}}^{+}$ center.

Amplitude modulation of a submillimeter NH3laser with two-photon pumping

It was established that efficient amplitude modulation of the output power of a submillimeter NH3 laser with two-photon pumping may be achieved by deviation of the microwave source frequency. The limiting modulation frequency was 0.5 MHz.

Superelastic collisional excitation of a strontium plasma by one- and two-photon laser pumping.

Fast superelastic electron heating by collision quenching of one- and two-photon laser pumped states has been demonstrated in a relatively cold strontium plasma created by two-photon ionization of strontium vapor contained within a crossed heat-pipe oven.

Time characteristics of a traveling-wave laser subjected to two-photon picosecond optical pumping

An image-converter streak camera with picosecond time resolution was used in a study of the kinetics of formation of pulses in a traveling-wave laser in which molecular dye solutions were subjected to two-photon optical pumping. An analytic expression was obtained for the lasing threshold of a nonresonator traveling-wave laser in the case of pulsed (τp τe) and quasicontinuous (τp > τe) pumping. Satisfactory agreement was obtained between the calculated and experimental lasing threshold. The kinetics of the compression of output pulses, determined as a function of the pump radiation intensity, was described by rate equations. At pumping rates up to 10 times the threshold a qualitative agreement between the experimental and calculated results was obtained employing a two-band energy model of the dye with a short (compared with the duration of the pump pulses τp) vibrational relaxation time τe. At rates of excitation well above the threshold the kinetics of compression and delay changed, and the output pulses were split into two components, which was interpreted (in the specific case of rhodamine 6G) using a four-band energy scheme. A practical conclusion of this investigation was in the form of recommendations on the use of the proposed approach as a simple method for generating high-intensity single picosecond superradiance pulses of duration τsr with frequency up-con version and a compression coefficient τp/τsr ~ 10.

Dimer laser action in Na2by collisional energy transfer

A number of molecular laser lines in Na2 around 800 nm have been observed by collisional energy transfer. Two-photon pumping of 5s and 4d levels of Na was employed to stimulate the A-X laser transitions. The processes responsible for the energy transfer are discussed. A small signal gain coefficient is calculated and compared with the measured value.

15NH3laser with two-photon optical pumping

Optical pumping with radiation from a pulsed TEA CO2 laser emitting the 9R(46) line resulted in stimulated emission from the isotopically substituted 15NH3 ammonia molecules at the frequency of 718.92 ± 0.15 cm−1 . It was found that the (2,9,1)−→(1,10,1)+ mode ν2 was emitted as a result of two-photon (0,7,1)−→(2,9,1)− optical excitation of the 15NH3 molecules. Stimulated emission occurred at 15NH3 pressures in the range 1–50 Torr, the maximum energy was 1 mJ, and the differential efficiency was 0.3%. The experimental results yielded the two-photon coefficient of absorption of the pump radiation as a result of the (0,7,1)−→(2,9,l)− transition in the 15NH3 molecules: β = 1.19×10−8cm/W.

Time-delayed probe spectroscopy in two-photon-pumped systems.

We study transients in resonantly coupled three-level systems. Two of the levels are coupled by intense two-photon pumping, and the third one provides a probing level. Adiabatically eliminated levels appear in effective system parameters. Experimentally, this model is applicable, e.g., in resonantly enhanced parametric and harmonic generation in atomic vapors. A distinguishing feature in the system is the appearance of ac Stark shifts in the probe spectra when pumping at the two-photon resonance. The nutation signal is shown to give information on the effective two-photon Rabi frequency and on the decay rate of the dipole-forbidden two-photon coherence. Free-induction decay is strongly dominated by population-induced effects; Raman-like peaks introduced by Stark shifts may show large instantaneous gain. Gaussian pump pulses are investigated to investigate effects arising from the temporal sweeping of the two-photon Rabi flipping and the modulation of the Stark shifts. The results also provide relevant information on the gain dynamics of coherently pumped lasers.

Parametric noise in a nonlinear frequency up-converter of infrared signals by two-photon pumping of 3S–3Dand 3S–5Stransitions in sodium vapor

A systematic analysis was made of the spectral characteristics of resonance four-photon parametric conversion of infrared radiation as a result of two-photon resonance pumping of the 3S–3D and 3S–5S transitions in sodium and the influence of these characteristics on the threshold sensitivity of a parametric conversion detector was investigated. An experimental study was made of the characteristics of the noise radiation generated as a result of hyperparametric scattering. The results obtained can be used to select the optimal parameters of high-sensitivity detectors of weak infrared signals by parametric conversion in alkali metal vapors.

Hyper-Raman scattering and four-wave parametric interaction in two-photon pumping of metal vapors

Investigations are made of hyper-Raman scattering and four-photon parametric processes in two-photon excitation of metal vapor. The laws of propagation of infrared and ultraviolet radiation generated in a metal vapor medium by these processes are found for the steady-state interaction. The nonlinear polarization of the medium is obtained in terms of elements of the atomic density matrix allowing for saturation by the pump field and for the influence of collisions. The spectral and tuning characteristics of the converted radiation are studied and a comparison is made with experimental data. A dip observed in the infrared radiation spectrum for hyper-Raman scattering and its broadening are explained. A detailed discussion is given of the role of collisions that substantially narrow the tuning range of the infrared radiation in hyper-Raman scattering.

Electron stimulated Raman scattering and four-wave interaction in barium atomic vapor pumped by tunable ultrashort light pulses

A phosphate neodymium glass laser emitting picosecond pulses tunable in the 1.05–1.07 μ range was developed to study nonlinear optical processes in atomic barium vapor. Its temporal characteristics were investigated using a modified second harmonic beam method. Electron stimulated Raman scattering and four-photon parametric conversion in atomic barium vapor were used to obtain efficient conversion of the third harmonic of the picosecond phosphate laser (350–356 nm) to the Stokes (580–600 nm) and anti-Stokes (250–253 nm) waves. The highest conversion quantum efficiency for the Stokes wave was 15%. Electron stimulated Raman scattering in an (6s2)1S–(6s7s)1S–(6s6p)1P0 system, having a strongly forbidden first transition, was recorded for the first time. In the same system, two-photon pumping generated four-photon parametric superradiance and it was found that the signal and idler waves had anomalously broad spectra (wider than 100 cm−1).

Two-photon hybrid resonance laser and photodissociation laser by two-photon pumping covering a wide wavelength region in the potassium vapor

This paper reports the results about the laser generation based on the two-photon hybrid resonance and on the photodissociation by two-photon pumping covering a wide wavelength region respectively. In the former, 3.66, 3.64, 3.16, 3.14, and 2.71 μm laser lines were obtained by collision energy transfer from a potassium dimer in an excited state to the potassium atom in the ground state, and then followed by the resonance excitation of the potassium atom from the 4P to 6S state. In the latter, 2.71, 3.14, and 3.16 μm dissociation laser lines were obtained by two-photon pumping of the potassium dimer covering a wide pumping range about 650 Å at the red wavelength region.

Observation of superfluorescence and stimulated emission in Bi I after nonresonant two-photon pumping

We report the observation of superfluorescence and of stimulated emission in the near-infrared at 965.69 nm in atomic Bi. The atoms are prepared in the 6p2(3P0)7p3/2 upper state by nonresonant two-photon excitation. The cooperative character of the emission is demonstrated by the delay of the light pulses and their N2 dependence upon the atomic density.

Light amplification in CdTe and InSe under two-photon pumping

Photoluminescence measurements in CdTe and InSe under high intensity two-photon pumping are reported. The relative non-linear absorption coefficients of both materials have been measured. Stimulated emission spectra of both CdTe and InSe show an amplification effect due to excitonic recombination involving a cooperative process; the related optical gain coefficients have been measured.

Time-resolved infrared-ultraviolet double resonance in D 2CO and HDCO: Spectroscopic applications

Spectroscopic results, from an extensive study of rotationally resolved infrared-ultraviolet double resonance (IRUVDR) effects in the molecules D 2CO and HDCO, are reported. The experiments involve rovibrational pumping (in the ν 4 or ν 6 bands of D 2CO and the ν 5 or ν 6 bands of HDCO) and rovibronic probing of the A 1A 2 ← X 1A 1 electronic system (in the 4 0 1 or 6 0 1 bands of D 2CO and the 5 0 1 or 6 0 1 bands of HDCO) with visible-fluorescence detection, using sequential pulsed excitation by CO 2 and dye lasers. A remarkable result is the observation of IRUVDR rovibronic features in the very weak and heavily overlapped 6 0 1 band of D 2CO, which has not previously been detected by conventional means. Further experiments which probe the 4 1 2 band of D 2CO are interpreted in terms of single-photon rovibrational pumping in the (2 ν 4 - ν 4) hot band, rather than two-photon pumping in the 2 ν 4 band. The results reported are obtained under effectively collision-free conditions, achieved by maintaining the product of pump-probe delay and sample pressure below ∼10 nsec Torr; collision-induced rotational and rovibrational relaxation is apparent when this product is increased. Other aspects of the IRUVDR technique which are considered include: the relation of IRUVDR results for D 2CO and HDCO to coincidences between CO 2-laser and molecular rovibrational frequencies, previously demonstrated by sub-millimeter optically pumped laser emission, infrared-radiofrequency double resonance, and Lambdip absorption studies; the role of saturation broadening in promoting multiple coincidences of molecular rovibrational transitions with a given CO 2-laser line; relevance to mechanisms of infrared multiple-photon excitation of D 2CO; inconsistencies between observed IRUVDR signal intensities and those anticipated from rovibronic transition probabilities.

Two-photon optical pumping of NH3in a multipass cell

A multipass cell was used in optical pumping of ammonia molecules by CO/sub 2/ laser radiation. Several new lasing lines were observed in the case of two-photon optical pumping of the NH/sub 3/ molecule at wavelengths in the range 16--35 ..mu... The output power of the various lines was in the range 10--50 kW. The divergence of the resultant radiation was diffraction-limited. A theoretical study was made of the two-photon pumping process. A stable (on the frequency scale) maximum was found in the gain profile of the output radiation. It was concluded that it should be possible to increase the energy and extend the emission spectrum of an ammonia laser pumped by double-photon absorption.

Infrared laser emission in atomic sodium vapor pumped by collision assisted laser excitation

A collision-assisted two-step two-photon pump mechanism for generating a population inversion among the 5 2S and 4 2P levels in atomic sodium is reported. By tuning a pulsed dye laser to the 3 2P to 5 2S resonances IR laser emission on the 3.415 μm (5 2S 1/2-4 2P 3/2) and on the 3.408 μm (5 2S 1/2-4 2P 1/2) lines is observed. The conversion efficiency is e stimated to be 5% and up to 5W IR peak power is observed in the present experimental setup.

New cw two-photon pumped and Raman fir laser lines in 14NH 3 and 15NH 3

Application of infrared-microwave two-photon pumping on 14NH 3 and 15NH 3 yields 17 new cw laser lines in the far infrared. In addition a new Raman laser line in 15NH 3 is found.

Two-photon optical pumping of CO(A1Π

By a two-photon transition, we have selectively excited CO in some levels of the A1π(ν = 0) state. Measurements of lifetimes and self-quenching cross sections have been achieved, which exhibit the influence of local perturbation of the A1Π state.