Intracavity Absorption Research Articles

External photoacoustic detection of a trace vapor inside a multimode laser

We combine highly sensitive intracavity absorption spectroscopy in a multimode laser with external photoacoustic detection, providing high detectivity. Photoacoustic measurements of the intracavity iodine concentration in a Rhodamine 6G laser are compared with simultaneous spectral recordings. They demonstrate slightly improved overall sensitivity and a greatly enhanced dynamic range of 5 orders of magnitude that may be shifted along the absolute scale of absorber density.

Dynamics of the intracavity absorption in the spectrum of a Co:MgF2 laser emitting for up to 1 ms

The dynamics of the spectral dips, observed in detection of weak absorption lines by intracavity laser spectroscopy with a Co:MgF2 laser, was investigated. When the pumping rate exceeds the threshold by factors of 2.6 and 1.4, the intracavity absorption increases linearly with increase in the duration of lasing to 0.5 and 1 ms, respectively. A deviation from linearity is observed for longer times. This ensures a sensitivity sufficient for measurement of the line absorption coefficient down to 3 × 10-9 cm-1 in the 1.6 — 2.5 μm spectral range of laser emission.

Bistability and self-pulsation in quantum-dot lasers with intracavity quantum-dot saturable absorbers

Self-organized In0.4Ga0.6As/GaAs quantum-dot single-mode ridge waveguide lasers with intracavity absorber were grown by molecular beam epitaxy. Bistability in the light–current characteristics of 3 μm single-mode edge-emitting laser was obtained by controlling the intracavity absorber voltage. Self-pulsation was also observed with a center frequency of 1.6 GHz and linewidth <10 MHz.

Photocurrent and electroluminescence in vertical-cavity surface-emitting lasers

We investigate both experimentally and theoretically the photocurrent and spontaneous emission spectra of vertical-cavity surface-emitting lasers below threshold. Special prominence is given to the spectral broadening due to finite numerical aperture. In the frame of a matrix formalism, photoresponsivity is determined as proportional to intracavity absorption, taking into account the angular dependence of the overlap factor, while an analytical approximation is proposed for the emitted flux as a function of the angle of collection.

Bias-controlled wavelength switching in coupled-cavity In0.4Ga0.6As/GaAs self-organized quantum dot lasers

Efficient wavelength switching is demonstrated in an In0.4Ga0.6As/GaAs self-organized quantum dot laser with an intracavity absorber section. A wavelength shift of ∼15 nm, believed to be caused by a shift of lasing between the bound states of the quantum dot, is obtained for a bias change of 6 V.

Piezoelectric InGaAs/AlGaAs laser with intracavity absorber

A novel InGaAs/AlGaAs laser integrated with an intracavity absorber grown on a (111)B GaAs substrate is demonstrated, making use of the piezoelectric effect. Transparency in the absorber section at the lasing wavelength can be achieved by using the blue-shifting characteristic of the absorption edge with reverse bias. This is shown by comparison of the lasing wavelengths with the absorption spectra of the laser structure under reverse bias. It is described how this approach could offer an alternative route to integrated laser-modulators.

Direct determination of triplet state influence on CW dye laser action – a new technique for intracavity absorption measurements

A new technique for intracavity absorption measurements is presented. The method is used to investigate triplet–triplet absorption of laser dyes. The triplet state population of the active medium is varied in a well-defined way. Due to the presented experimental setup, this can be done without changing any other molecular or optical parameter, which influences the laser action. In this way an increased triplet state population leads to an enhanced laser threshold which can be observed visually. Owing to the high sensitivity of the new technique, the triplet state influence on CW laser action can be studied simply by visual observation. No detection electronics is required. In order to analyse the experimental data, a refined theory of CW dye laser action is derived. The laser threshold of typical CW dye lasers can be calculated without numerical analysis. This theory can be applied even if the jet motion reduces the number of triplet molecules interacting with the dye laser beam to a dynamic equilibrium value. All experimental results are in good agreement with theoretical predictions. The triplet state properties, fundamental for laser action, can be extracted from the experiment. It turns out that the laser efficiency even of rhodamine 6G, one of the best laser dyes, is reduced significantly by triplet–triplet absorption. The triplet disturbance obtained for a new laser dye is found to be less than that of rhodamine 6G.

Fourier-transform intra-cavity laser absorption spectroscopy of HOD νOD=5 overtone

The newly developed high resolution Fourier-transform intra-cavity laser absorption spectroscopy (FT-ICLAS) was utilized to record the νOD=5 stretching overtone of HOD at a resolution of 0.05 cm-1 in the region 12550–12900 cm-1. The spectrum was rotationally analysed and the spectroscopic parameters were derived from nonlinear least-squares fitting. Good agreement of the observed with the calculated energy levels was achieved.

CO LASER MAGNETIC RESONANCE SPECTRUM OF 15N16O AND ITS ANALYSIS WITH SPECTRA OF 15N17O AND 15N18O

Employing the intracavity absorption technique,Lamb dip of the spectrum was obtained and the resolution and sensitivity of CO Laser magnetic resonance(LMR) spectrometer was greatly improved. By this technique, the X2Π3/2(υ=1←0) Zeeman transitions of 15N16O were observed with the Λ-doubling and hyperfine structures resolved. A correlative analysis of the LMR Spectrum of 15N16O with the previous available measurements was performed. The global least-square fit provided by far the most complete and the most accurate molecular constants of all the related isotopic species of 15NmO(m=16—18). The accuracy of these constants is improved by 1 or 2 orders. Many of the molecular constants including γ, AD, Δ01, Δ10, Δ00 were determined for the first time.

Dynamic behavior and applications of a three-contact vertical-cavity surface-emitting laser

We have developed a novel three-contact vertical-cavity surface-emitting laser (VCSEL) with an intracavity absorber for use in high-speed data communications. We demonstrate two distinct designs for our VCSEL and discuss the device physics underlying the behaviors of the two designs. Furthermore, we demonstrate a wide range of applications for these VCSELs, including optical intensity modulation, phase and amplitude modulation of a microwave optical subcarrier, optical bistability, self-pulsation, and optical disk readout.

Emission spectrum of a multimode dye laser with frequency-shifted feedback for the simulation of Rayleigh scattering

The output of a multimode cw Rh6G laser has been frequency-shifted by reflection from a moving mirror and used as a weak additional feedback to the laser for the experimental simulation of Rayleigh scattering inside the laser cavity. Reduced sensitivity of the laser spectrum to intracavity absorption has been observed, as well as increase of the laser bandwidth and of the emission bandwidth of individual longitudional modes. The effect of the frequency-shifted feedback on the laser dynamics is shown not to depend on the pump rate. The effect of both nonlinear mode coupling and Rayleigh scattering on laser spectral dynamics has been determined from a model and from the measurements. The product of spectral saturation time and emission bandwidth of a laser mode is found constant. Rayleigh scattering seems to be the principal mechanism governing the spectral dynamics and determining the stationary bandwidth of the modes in solid-state lasers.

Possible self-oscillatory processes in the radiation field of a CO2 laser with a nonlinear absorbing element

A theoretical investigation is made of the dynamics of operation of a wide-aperture CO2 laser containing an intracavity absorption cell with an SF6 — NH3 gas mixture. It is shown that one can select such parameters of the laser that the profile of its optical field is of self-oscillatory nature in a wide range of pressures of the active and nonlinear media and for various cavity dimensions. Self-wave generation is influenced mainly by the vibrational — vibrational exchange between nitrogen and CO2 and by the vibrational — translational relaxation of the lower laser-active level of the CO2 molecule. Each of these processes favours self-wave generation and, depending on the composition of the active medium, one or two self-wave systems can be observed. The results are obtained for situations attainable in electric-discharge and electron-beam-controlled discharge lasers.

Intracavity laser spectroscopy with a Co:MgF 2 laser

Absorption spectra of atmospheric carbon dioxide and water vapor are recorded by intracavity laser spectroscopy technique using a broadband Co:MgF 2 laser, tunable over the range from 1.6 to 2.5 μm. Pulsed Co:MgF 2 laser has been operated at room temperature. The dynamics of intracavity absorption was studied for the generation time of 0–100 μs. The observed linear dependence of sensitivity on the generation time demonstrates that Co:MgF 2 laser can be utilized for high sensitivity intracavity laser spectroscopy measurements in the near infrared (IR) region.

Excitability in a nonlinear optical cavity

We establish a nonlinear optical cavity to be excitable. Excitability in this system is shown to originate from the combined dynamical effects of nonlinear intracavity field saturation and temperature-dependent absorption in the medium on two different time scales. The model may be experimentally realized using optical bistable devices with possible useful applications.

Recording of selective intracavity absorption at doubled frequencies of multimode laser radiation

We carried out measurements of the spectral distribution of wideband dye laser generation intensity within the limits and in the vicinity of an absorption line with its simultaneous recording at the frequencies of the fundamental and second harmonics of laser radiation. In the laser cavity we placed optical cuvettes with active and absorbing media, as well as selecting and nonlinear-optical elements. We show that at double frequencies the contrast of the narrow-band hole in the multimode laser generation spectrum increases. The gain in the concentration sensitivity of measurements depends in this case on the value of the absorption coefficient being determined.

Iodine-stabilized extended-cavity diode lasers at λ ≈ 633 nm: result of an international comparison

A comparison of three 127I2-stabilized extended-cavity diode lasers has been carried out between the Danish Institute of Fundamental Metrology (DFM) and the Bureau International des Poids et Mesures (BIPM). Two of the lasers are stabilized using intra-cavity saturation spectroscopy, the third one using extra-cavity saturation spectroscopy. All lasers are locked using the third harmonic detection technique on different hyperfine components of the P(33)6-3 transition. The range of frequency differences measured during the four days of the comparison was from -340 kHz to 150 kHz. The large fluctuations are due to the poor repeatability of the extended-cavity diode lasers with intra-cavity absorption cells (ECL4 and BIREL1-1). The frequency stability and repeatability of the diode laser (ECL1) using an external absorption cell is roughly one order of magnitude lower in performance than the He-Ne lasers. Using an iodine-stabilized He-Ne laser (DK3) as reference and the recommended values given in the practical realization of the definition of the metre, we found a mean offset from the expected frequency difference between ECL1 and DK3 of -12 kHz and a standard uncertainty of 10 kHz.

Measurement of density in a discharge by intracavity laser absorption spectroscopy and CW cavity ring-down spectroscopy

Two highly sensitive and quantitative absorption techniques have been applied to the detection of in an argon-5% silane DC discharge, the new method of CW cavity ring-down spectroscopy (CWCRDS) and intracavity laser absorption spectroscopy (ICLAS). Doppler-limited absorption lines of the transition around 580 nm could be observed. By using the rotational constants and the electronic transition moment available in the literature, we have calculated the line intensity of some specific rovibronic transitions from which we deduced the concentration of in the discharge to be about . Taking into account the signal-to-noise ratio, concentrations as small as a few times can be detected by both methods. We also observed a weak broadband absorption of several due to the dust particles formed in the plasma volume, which for particles of 1 nm diameter would correspond to a few times . The performances of ICLAS and CWCRDS are compared.

Absorption spectroscopy of SiH2 near 640 nm

The à 1B1–X̃ 1A1 absorption spectrum of SiH2 has been observed using intracavity laser absorption spectroscopy with an equivalent path length of up to 13.0 km and the à 1B1(0, 0, 0)–X̃ 1A1(0, 0, 0) band near 640 nm recorded for the first time. The silylene radical was generated in a continuous discharge in a flowing mixture of silane in argon, giving a concentration of the order of 1010 SiH2/cm3. The spectrum spans the region between 15350 and 16100 cm−1. Rotational transitions have been assigned to levels up to J=16 and Ka=9, with ΔKa up to 5, ΔKc up to 4. Perturbations have been detected in the spectrum, due to Renner–Teller and spin-orbit interactions between both electronic states and the 3B1 state, predicted to be between them. However, the strength of the irregular perturbations affecting the rotational states of à 1B1(0,0,0) state is found to be much weaker than that affecting the other (0, v2′, 0) levels previously studied. The analysis of the spectrum has allowed the determination of the rotational constants of the 1B1 (0,0,0) level, and a new estimation of those of the vibrational and electronic ground state. The geometry of the excited electronic level has also been determined for the first time from accurate experimental data. A change in the structure of this molecule takes place with this transition, the equilibrium angle opening from 92° to 122.4°, while the bond distance is reduced from 1.51 to 1.485 Å.

Coherent-absorber mode locking of solid-state lasers

We study solid-state laser mode locking in the self-induced transparency regime of an intracavity absorber. Depending on the absorber dephasing, pulse energy, and resonator dispersion, we find stable coherent 2pi -pulse operation, pulse splitting, oscillatory pulse shapes, and smooth transition to incoherent saturable-absorber mode locking.

Synchronization of a laser system to a modulation signal artificially constructed from its strange attractor

We demonstrate experimentally and numerically that a laser system can be synchronized to any chaotic pulsation intrinsic to the system by modulating a system parameter. A sequence of pulses is prepared, the heights and interpulse intervals of which are artificially constructed from the correlation function of a prerecorded chaotic pulsation. When an on-off modulation signal obtained from this pulse sequence is applied to intracavity absorption, the laser reproduces the chaotic time sequence.