B. Ståhlberg

Nonlinear forward scattering of resonant laser light from excited neon systems

We investigate forward scattering induced by a powerful single mode dye laser interacting with excited neon systems. We present experimental data obtained with the three transitions: 1s4(J=1)-2p3(J=0), 1s2(J=1)-2p1(J=0), and 1s5(J=2)-2p4(J=2). The lineshape dependences on the gas pressure, the laser power and the laser field fluctuations are discussed in the context of published theories. Our data resemble the calculated lineshapes in which fluctuations in the interaction processes between atoms and laser fields are taken into account. In atomic systems having more complex level degeneracies [1s5(J=2)-2p4(J=2)] signal structures expected from higher order nonlinear coherences can occur. To theoretically reproduce these lineshapes a simple J=1→J=0 model is fully appropriate provided that the level with J=1 has a narrow width.

Laser-induced dispersion in a three-level system

A theoretical calculation of the polarization changes of a weak probe laser beam as it traverses a strongly pumped gaseous atomic medium is presented. The medium is chosen to be a three-level cascade (J = 0–J = 1–J = 0) system. The polarization of the probe changes from linear to elliptical owing to the asymmetrical population transfer induced by a strong, circularly polarized pumping laser beam. We study this phenomenon as a function of laser intensities, laser detunings, and the relaxation parameters of the medium. We compare the predictions of the theory with results obtained from experimental studies of the neon 1s4(J = 1)–2p4(J = 2)–3s2(J = 1) system.

Forward scattering induced by laser fields in atomic J=1→J=0 systems

Abstract We investigate resonant forward scattering of laser radiation. Calculations based on the semiclassical laser theory are performed up to the second order in the laser intensity. The response of the atomic J =1→ J =0 transition to a laser beam is considered. Experimental verification of the theoretical lineshapes is carried out using a neon gas absorber. The agreement between the calculated results and the measurements is excellent and indicates that higher order nonlinearities such as hexadecapole couplings are not easily discerned in the lineshapes.

Stabilization of a single mode dye laser to a HeNe laser using magnetic modulation of a three-level neon system

Abstract We describe a simple stabilization method where a tunable single mode (594.5 nm) cw dye laser is locked to a stabilized (633 nm) HeNe laser via the 1s 5 -2p 4 -3s 2 Ne transitions. By using longitudinal Zeeman modulation of the absorber and a circularly polarized HeNe laser beam derivative signals are obtained. Utilization of routine lock-in techniques produces a dye laser frequency stability comparable with that of the reference HeNe laser.

Laser wavelength measurement with a Fourier transform wavemeter

We report results from spectral measurements in the optical and near infrared region performed with a Fourier transform wavemeter. Characteristics of a variety of lasers and the performance of the wavemeter have been studied. The group of cw lasers measured in this work is comprised of a 1550-nm multimode diode laser, an 820-nm single-mode diode laser, a 594.5 nm dye laser, and He-Ne lasers at wavelengths of 1523, 633, and 543 nm. The Fourier transform wavemeter is powerful in multimode laser investigations and in long-term frequency stability determinations. The measurements show that the wavemeter also easily reveals very low power laser modes; it is suitable for the investigation of the single-mode purity of lasers. The line position uncertainty <10(-8) can be concluded in the measurements with polarization-stabilized 633- and 543-nm He-Ne lasers.

Collision-induced resonances in Doppler-broadened systems

Abstract This paper discusses the occurrence of collision-induced resonances in a Doppler broadened system. They consist of a narrow coherent signal and a broad population transfer signal. The latter has a strength proportional to the rate of phase perturbing processes. The specific example of Hanle level-crossings is discussed in detail. The disappearance of the broad resonance is shown to derive from cancellation of coherent and incoherent contributions. Their origin is elucidated by a diagrammatic density matrix perturbation expansion. Finally the results are verified experimentally on the red transition in a Ne gas. The narrow and broad resonances are identified, and the ratio of their strengths is shown to disappear with the pressure in the sample cell.

Measurements of 22Ne-20Ne isotope shifts by laser-induced line narrowing in three-level systems

Application of laser-induced absorption line narrowing (ALN) to neon isotope shift investigations in the stretched three-level systems 1s5-2p4-3s2 and 1s4-2p4-3s2 is reported. The measurements have been performed with a frequency and intensity-stabilized 633-nm He-Ne probe laser and with a tunable single-mode R6G dye laser. Utilization of longitudinal magnetic modulation to the neon gas absorber yields background-free resonance signals. Measurements of 594.5-, 609.6-, and 633-nm 22Ne-20Ne isotope shifts result in (1712 ± 8) MHz, (1753 ± 8) MHz, and (904 ± 8) MHz, respectively. These values agree with previous data.

Laser induced polarization properties of a neon three-level system

Abstract We investigate polarization spectroscopy as a probe of broken left-right symmetry in neon atoms. In the cascade 1s 4 -2p 4 -3s 2 three-level system the upper transition is probed by a linearly polarized weak HeNe laser beam. The symmetry of the lower level is broken by a circularly polarized strong dye laser beam acting on the lower transition. We present the experimental setup, the resulting measurements and a comparison with a straightforward theory of symmetry breaking.

Construction and alignment of a compact wavelength meter for cw lasers

Abstract We describe a simple and reliable automatic fringe-counting interferometer featuring a real-time display of cw laser wavelengths. The wavemeter and its reference laser constitute a compact construction and offer easy operation. The accuracy of the system is better than one part in 106.

Modulation techniques in three-level laser spectroscopy of a neon discharge

Abstract The interaction between a chopped laser pump beam and a neon discharge is compared with the interaction between the unchopped beam and a Zeeman modulated discharge response. Experimental sensitivity and reliability is obtained by unconventionally utilizing a fixed frequency and intensity stabilized single mode 633 nm He-Ne laser as a probe and a tunable single mode dye laser as a pump. Neon atoms in the metastable first excited state 1s 5 are pumped to the lower energy level of the (633 nm) 2p 4 -3s 2 transition. Pumping to uncoupled nearby levels of 2p 4 is also studied. Several gigahertz wide backgrounds originating from the plasma ionization changes induced by the chopped pump beam are shown to be eliminated by the more adiabatic magnetic modulation technique. Connections between high resolution spectroscopy, polarization spectroscopy line shape asymmetries and optogalvanic spectroscopy are discussed. The usefulness of the magneticmodulation technique in high resolution studies is demonstrated.