Laser Emission Frequency Research Articles

Frequency Manipulation of THz Bound-to-Continuum Quantum-Cascade Lasers

The laser emission frequencies of existing designs are controlled by uniform thickness transformations. Experimental results from a total of ten wafers are presented demonstrating a predictable shift in the emission wavelength concurrent with an anticipated alteration in electrical transport. Wafers based on a design around 2.9 THz produced a frequency shift of 0.35 THz. Furthermore, a 2.5% thickness reduction in our 2-THz design saw a 0.1-THz frequency shift and changes in electrical transport predicted by simulations.

Diode laser coupled to an atomic line by incoherent optical negative feedback

We report on experiments using optical negative feedback with orthogonal polarization to control the emission frequency of single-mode AsAlGa diode lasers. We obtain linewidth reduction and absolute frequency stabilization by injecting into the semiconductor laser a beam whose intensity is controlled by a Cs–D2 absorption line shape.

Analysis of accuracy of measurement by Doppler laser meters

We discuss the accuracy analysis of laser meters based on the Doppler effect and used in the measurement of automobile velocity. Usually, the systematic errors are assessed during calibration and are eliminated by instrumental means. Nevertheless, it is impossible to eliminate random errors. Their analysis is also important for such measurements, and this has been less extensively analyzed in scientific papers. A probabilistic method is used for error analysis assuming that only random errors are present. The accuracy of measurement by Doppler meters depends mostly on parameters of two kinds—laser source stabilization, measuring laser emission frequencies, and the errors in determining the emission speed in the atmosphere. Such analysis shows a value of the random error occurring during the measurement of automobile speed that also can be applied for assessment of other kinds of measurements of moving objects.

CO Laser Absorption Coefficients for Gases of Biological Relevance: H2O, CO2, Ethanol, Acetaldehyde, and Ethylene

The pressure-broadened spectra of water vapor, carbon dioxide, ethylene, ethanol, and acetaldehyde were recorded with the use of a liquid nitrogen-cooled CO laser-based photoacoustic spectrometer. The results obtained for CO2 and H2O gases were compared with those from the Hitran database. The absorption coefficients of ethylene, ethanol, and acetaldehyde on CO laser emission frequencies were determined as well. Finally, the measured spectra were used in a multicomponent analysis of trace gases released by pears ( Pyrus communis, cultivar Conference).

Frequency-sweep generation by resonant self-injection locking

We report a novel application of self-injection locking. A diode laser is injection locked to its own frequency-shifted emission. By resonant phase modulation of the fed-back light, the laser's emission frequency is shown to swing periodically through the locking range. The laser operates as a sweep generator driven by resonant self-injection locking.

Global solutions and attractors of a Maxwell-Bloch Raman laser system in two transverse dimensions

We study a Maxwell-Bloch system describing the dynamics of single-longitudinal Raman lasers in the two transverse space dimensions. Raman lasing is generated by a coherent external pump laser, as a three-wave interaction involving two optical and one material wave. On the other hand, a two-level laser involves incoherent external pumping through, for example, an electrical discharge or flashlamp. Raman lasers have the advantage of being tunable and display a novel explicit nonlinear detuning between the pump and laser emission frequencies. Consequently these lasers exhibit much richer nonlinear dynamics. We establish the global existence of classical solutions, and show that for periodic domains the dynamics is governed by a global smooth attractor of finite dimensions. We explain the structures of nonlinear interactions and couplings that lead to the time asymptotic smoothing. We also construct mild solutions with the dispersive Strichartz inequality for rough but spatially decaying data (in , ) on the whole plane, which physically corresponds to the absorbing boundary condition.

Stability and dynamical properties of the coexisting attractors of an external-cavity semiconductor laser

Coexisting attractors, which arise from different external-cavity modes of the same longitudinal mode of the solitary laser, retain distinct stability properties, particularly when the laser is biased far above threshold and subjected to moderately strong optical feedback from a distant reflector. When the laser is modeled by the Lang and Kobayashi equations with additional gain nonlinearity, the dynamics is limited to external-cavity attractors that develop from the external-cavity modes which have a positive but not too large frequency shift with respect to the solitary laser emission frequency v 0 . Although relaxation oscillations about these externalcavity modes are the first to become undamped as the feedback intensity increases, the attractors that arise from these modes remain stable over the largest range of feedback strengths. Stronger feedback destabilizes the individual attractors, creating new solutions which form from their ruins. At the beginning of the merging, the attractor ruins are not equally visited; the most visited ruins are those of the attractors last destabilized. We explore and explain these results by examining the dynamics of the laser when operating on a single externalcavity attractor. @S1050-2947~98!08101-3#

Prospects for frequency stabilisation of metal vapour lasers

A proposal is made for extending the range of laser wavelengths in which measurements are possible with the precision expected of frequency standards. The proposed stabilisation of the emission frequency of metal vapour lasers is by reference to 127I lines.

Fiber optic temperature sensor using sampled homodyne detection

A method of homodyne detection using laser emission frequency modulation and sampling of the interferometer output signal is described for a temperature sensor using a Mach-Zehnder all-fiber interferometer configuration. Both ac and dc signal detection are possible with this scheme. Temperature changes over the 5-80 degrees C range are measurable with a resolution of 1.4 mK by fringe counting and electronically determining the slope of the phase change.

Electrostatic FEL frequency stabilization: optical design and amplifying medium

We propose a resonator optical system usable from 100 μm (free propagation in the wiggler) to 1 mm (guided propagation) for an electrostatic FEL. This resonator allows single mode selection. The oscillating medium eigenfrequency, which depends on the electron energy and on the wiggler local spatial period, must be the same as the laser emission frequency. We propose to make the electrons' accelerating potential grow, to compensate for the extracted energy, and to create an electrostatic field in the wiggler during laser startup, so that the tapering is compensated for.

Influence of the line overlap on the spectral and energy characteristics of CO electron-beam-controlled lasers

A time-dependent kinetic model of a CO electron-beam-controlled laser, allowing for the PP and PR overlaps of the emission lines, is used in an investigation of the output characteristics in a laser. It is shown that, beginning from pressures of ~ 0.1 atm (T ~ 100 K), the line overlap alters significantly the vibrational–rotational emission spectrum and, in particular, many of the P lines are no longer observed. At pressures of the order of or higher than the atmospheric value the line overlap reduces considerably (by up to tens of times) the efficiency and limits greatly the feasibility of continuous tuning of the laser emission frequency.

Deep-water fiber-optic hydrophone

A prototype hydrophone was constructed using a He–Ne laser coupled optically to a single-mode fiber waveguide. An active homodyne system for recording of the signal was developed and tested. This system utilized control of the laser emission frequency and its phase sensitivity limit was 10 − 5 rad/Hz1/2. Winding of the waveguide on an elastic mandrel increased the hydrophone sensitivity by 45 dB.

Determination of losses in lithium niobate optical waveguides using a single-frequency semiconductor laser

A description is given of a method for determination of the optical losses in a waveguide using a waveguide resonator in which the difference between the paths of interfering beams is altered by varying the emission wavelength of a single-frequency semiconductor laser. The measurements made on lithium niobate waveguides yielded the losses of 0.6 dB/cm at the rate of change of the laser emission frequency when the pump current was altered at a rate of 1.3 GHz/mA.

Spectrometer based on injection lasers emitting near-infrared radiation

A two-beam spectrometer utilizing injection lasers emitting in the near infrared was constructed. The spectrometer utilizes rapid scanning of the laser emission frequency followed by recording with an analog–digital converter. The spectrometer parameters are as follows: a spectral resolution of at least 2 × 10 −3 cm−1, a response time 50 ns, and a detectivity amounting to 0.0003% of the incident power carried by one pulse.

Carbon dioxide absorption of He–Ne laser radiation at 42 μm: characteristics of self and nitrogen broadened cases

A laser resonance absorption spectrometer is used to investigate the characteristics of both self and nitrogen collision broadened carbon dioxide in resonance with He-Ne laser radiation at 4.2 microm. The absorption coefficient in these broadening conditions has contributions from the R(28) to R(34) absorption lines of the nu(3) CO(2) spectrum. The Fletcher-Powell optimization method is used to reduce the raw absorption data and to find the best value average collision broadening coefficient and laser emission frequency for a Lorentzian line shape model of the contributing lines. Pure carbon dioxide absorption in a pressure range of from 0.0016 atm (1.25 Torr) to 0.33 atm (250 Torr) is described well by the model with an average self broadening coefficient of 0.084 +/- 0.008 cm(-1) atm(-1) for laser frequencies located at either 2370.591 +/- 0.020 cm(-1) or 2371.135 +/- 0.019 cm(-1). Nitrogen broadened carbon dioxide in the total pressure range of from 0.13 atm (100 Torr) to 1.18 atm (900 Torr) is characterized by the same model with the laser frequency at 2371.102 +/- 0.007 cm(-1) atm(-1). The average absorption coefficient for low concentrations of carbon dioxide in a 1-atm total pressure nitrogen environment has been determined experimentally as 9.90 +/- 1.49 cm(-1) atm(-1). All the listed results are at 296 K.

Interferometric optical path difference measurement using sinusoidal frequency modulation of a diode laser

We describe a technique applicable to interferometric systems illuminated by a laser diode, whereby the optical path difference is recovered by means of sinusoidal modulation of the laser emission frequency.

Stress-induced tuning of a diode-laser-excited monolithic Nd:YAG laser

We report the application of a stress-induced change in the cavity of a monolithic Nd:YAG laser as a means for precisely tuning the laser's emission frequency. By using a piezoelectric transducer to vary the applied stress, we can scan the laser emission frequency rapidly and monotonically over as much as 76.5 GHz. As a consequence of the stress-induced birefringence, the device can also be operated simultaneously in two orthogonally polarized modes that exhibit different tuning rates with applied stress.

Doubling of the emission frequency of CO lasers with an efficiency of 3%

A study was made of second-harmonic generation in a high-quality ZnGeP2 crystal (absorption coefficient 0.1 cm−1 ) . The second-harmonic power ranged from 2.45 to 4 mW when the CO laser power was 81.25–194 mW. The maximum external efficiency of second-harmonic generation reached 3%.

Causes of scatter of the emission frequency of gas lasers stabilized using the Lamb dip

Frequency shifts of the order of tens of megahertz were induced by misalignment or asymmetric stopping down of a resonator of a compact He–Ne laser the emission frequency of which was stabilized using the Lamb dip. These shifts were due to the fact that motion of a mirror along the resonator axis was accompanied by angular scanning because of the excitation of higher harmonics of mechanical vibrations of a mirror together with its piezoelectric ceramic base. Parasitic amplitude modulation produced by such vibrations shifted the frequency of the power minimum. In the case of symmetric stopping down of the laser the shift of the emission frequency did not exceed 2–4 MHz, indicating that in this case the Garside effect and the lens-like action of the inhomogeneous population inversion region had little influence.

Frequency resonance in a three-mode laser with a nonlinearity absorbing cell

A three-mode method for the separation of frequency resonances in a laser with a nonlinear absorbing medium is proposed. The results are reported of a study of frequency resonances in an He?Ne/I2 laser emitting the wavelength of 0.63?. It was found that the three-mode method ensures considerable enhancement of the frequency resonance gain compared with the two-mode method, which is desirable in spectroscopic applications of lasers and in the stabilization of the laser emission frequency.