Design and operation of a very large ring laser gyroscope

The design and initial operation of a vertical square He-Ne ring laser G0 with a perimeter of 14 m is discussed. This builds on earlier demonstrations of the feasibility of large ring lasers (perimeter approximately 4 m) for single-mode gyroscope operation and with lesser pulling than navigation gyroscopes. With servoing of the rf excitation to yield single-mode operation, G0 gave a quality factor 1 x 10(12) and a Sagnac line with a frequency of 287.8 +/- 1.0 Hz induced by Earth rotation Omega(E). This has confirmed some vital questions over the feasibility of very large gyroscopes for geodetic measurements at the level of 10(-9) Omega(E).     

Doppler-induced unidirectional operation of a continuous-wave Raman ring laser in H2

We demonstrate stable operation of a diode-pumped cw Raman ring laser in diatomic hydrogen gas. Doppler-induced asymmetry between the the forward and the backward Raman gains leads to inherent unidirectional operation in the forward direction without intracavity optical elements. Use of the ring-cavity geometry dilutes the deleterious effects of thermal lensing and significantly reduces optical feedback to the pump laser.     

Unidirectional single-frequency operation of a Nd:YVO4 ring laser with and without a Faraday element

We demonstrate high-performance unidirectional and single-frequency ring-laser operation based on a diode-side-pumped Nd:YVO4 bounce amplifier, obtained in a ring system both with and without a Faraday rotating element. Ring-laser operation with intracavity Faraday unidirectional element produces 15-W cw output in a TEM00 and single-longitudinal mode with beam propagation parameter M2 < 1.1 with 35-W diode pumping. A novel non-Faraday-based ring laser uses a polarization-dependent output coupler and asymmetric polarization state in the birefringent Nd:YVO4 gain medium and is demonstrated to produce highly unidirectional (1200:1) single-frequency output of 14 W in a TEM00 mode with beam propagation factor M2 < 1.2 at 30 W of diode pumping.     

Laminar heat transfer over the initial section of a rectangular channel

The author describes a study, based on the linearized energy equation, of heat transfer over the initial section of a rectangular channel with a laminar incompressible flow and both uniform and nonuniform temperature fields at the inlet. Temperature and Nusselt number distributions over the channel perimeter are given.     

Fiber ring laser with a feedback mirror

We describe the spectral and power features of a ytterbium-doped double-clad photonic crystal fiber laser that is operated in a ring configuration with an external mirror that feeds back only one of its two output beams. We compare the operation of the laser with and without an external feedback mirror. We find that the feedback mirror reduces significantly the spectral and power fluctuations. It is also responsible for an interesting spectral phenomenon: The laser frequency is drifting periodically over 9 nm at a rate of 2 nm/s from a short wavelength to a longer wavelength and vice versa.     

Use of a ring laser for angle measurements

Measurement Techniques -     

Design of organic semiconductor laser structures for low threshold operation

Abstract

A theoretical analysis is undertaken of the optical mode confining properties of novel DFB and DBR ridge guided lasers fabricated from organic semiconducting materials. The analysis reveals that single transverse mode operation of the laser is possible by virtue of the increased lateral confinement and favourable values for gain threshold are obtained. A design for an efficient optical pumping arrangement is presented which makes use of the large Stokes-shift typical of organic semiconductors to employ a multi-periodic grating for both input and output coupling. Initial results of an analysis of this approach are also presented.     

Asynchronously modulated waves in a ring laser cavity

When modulated through the harmonic motion of one mirror, the counterpropagating waves in a ring laser oscillate out of phase. A solution to the wave equation is presented that satisfies both the time-dependent boundary condition and the resonance condition. This theoretical prediction is confirmed experimentally to leading order in terms that are inversely proportional to the speed of light. The method of solution is applicable to arbitrary phase modulation at more than one spatial location in the cavity. Potential uses include the reduction of the locking problem in ring lasers and the testing of higher-order kinematic effects in the theory of relativity.     

Sideband analysis and seismic detection in a large ring laser

Aring laser unlocked by the Earth's Sagnac effect has attained a frequency resolution of 1 part in 3 × 10(21) and a rotational resolution of 300 prad. We discuss both theoretically and experimentally the sideband structure of the Earth rotation-induced spectral line induced in the microhertz-hertz region by frequency modulation associated with extra mechanical motion, such as seismic events. The relative sideband height is an absolute measure of the rotational amplitude of that Fourier component. An initial analysis is given of the ring laser record from the Arthur's Pass-Coleridge seismic event of 18 June 1994.     

Random field of initial deflections and strength of thin rectangular plates

The use of an integral measure of initial deflections of thin plates, based on the strain energy, has proved to be of importance in studying the influence of the imperfections on the strength of plates subjected to in-plane compression. The energy measure allows for a straightforward definition of compound modes and for a computational determination of the lower bound strength. The last quantity may be essential for assessment of plate design strength considering the imperfections as a random field.     

Action of a rectangular pulse of a neodymium laser on porous metal targets

By the method of laser probing the erosion products of porous metal targets of Al and W under the action of a rectangular radiation pulse of a neodymium laser are investigated. The diameters of metal particles in the erosion flame measured using an electron microscope and using laser probing are fairly close, which indicates the reliability of control of particle sizes in real time by the laser probing method. The possibility of decreasing the particle sizes by reevaporating them is shown.A. N. Sevchenko Research Institute of Applied Physical Problems, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 2, pp. 179–183, February, 1994.     

Efficient operation of a solid-state adaptive laser oscillator

We present the results of a cw diode-pumped Nd:YVO4 laser oscillator based on a self-starting adaptive gain-grating resonator. Adaptive laser operation has been demonstrated with 12-W output for 37 W of diode pumping, producing a TEM00 mode that compensates for thermal aberrations. The issue of the finite aperture of the amplifier is discussed, and a design that incorporates an intracavity lens is used to improve the collection efficiency with severe thermal lensing at high pump powers. The powers of the beams involved in the resonator are compared with theory and are found to be in good agreement. Spectral and temporal behavior of the adaptive laser is investigated, and very interesting behavior is shown, including self-induced temporal modulation dynamics and a switching between a narrowband and a broad bandwidth of operation.     

Dual-wavelength operation of a self-seeded dye laser oscillator

We demonstrate simultaneous dual-wavelength operation of a self-seeded dye laser. The laser cavity consists of one dye cell, two pairs of grating and tuning mirrors, and two reflecting mirrors. This configuration can be decomposed with two grazing-incidence cavities and a standing-wave cavity. The self-seeded dual-wavelength output beams are collinear and independently tunable. We were able to vary the output powers at the two wavelengths smoothly by changing the cavity length of a master oscillator.     

Efficient double-clad thulium-doped fiber laser with a ring cavity

We have constructed a novel ring cavity for a double-clad thulium-doped fiber laser, by placing the fiber's 45 degrees angle-polished output end before the input end and relaunching the pump and the laser power into the fiber. This design can reduce reabsorption by using short fibers without loss of pump efficiency. The dependence of the laser's performance on the fiber's length and the output coupler's reflectivity is investigated experimentally and theoretically. With an 80-cm-long fiber, 2.7-W single-mode continuous-wave output is generated for 11.5 W of launched pump power.     

Mode matching for a passive resonant ring laser gyroscope

An analytical method of matching the mode of an input laser to the lowest-order mode of a passive resonant ring laser gyro is described, as are the steps in determining the location and focal length of cylindrical mode matching lenses. Results were obtained with no mode matching, with a compromise spherical lens, with horizontal mode matching only, and with the proper cylindrical mode matching lenses. Compared with no mode matching, the latter case shows that the amplitude of the lowest-order mode is increased approximately 2.5 times. In addition, the number and intensity of higher-order modes are reduced to near zero, and the relative intensity of the lowest-order mode to the higher-order mode increased from approximately 5 to approximately 60 times greater.     

Single-frequency Q-switched erbium-doped fiber ring laser by combination of a distributed Bragg reflector laser and a Mach-Zender interferometer

A single-frequency Q-switched erbium-doped fiber ring laser is implemented for producing a single frequency with 25-Mhz laser linewidth, Q-switched pulses with a high peak power at 1557.5 mm. The single longitudinal mode is selected by a distributed Bragg reflector fiber laser, and a fiberoptic Mach-Zehnder interferometer acts as a Q-switch. The peak power and the average power of the Q-switched pulses vary with the repetition rate.     

Dual-color operation of a laser diode under current and temperature control

We describe a novel method that operates a laser diode with dual colors. Our system requires no external optical parts but does require current and temperature control. We can use either a single color on a time-sharing basis or dual colors simultaneously. The difference between the wavelengths is -0.6 nm, which is as much as 10 times that generated by current control alone. Temporal stability of the generated two wavelengths and the response time of the wavelength change were confirmed through a number of experiments.