Mode Competition In Lasers Research Articles

Consistency of splitting frequency difference with longtudinal modes spacing variation in Zeeman dual-frequency laser

Phase anisotropy in laser resonant cavity will bring about an influence on laser frequency and polarization, such as laser frequency splitting, of which the frequency difference is determined by their introduced phase retardation. For a helium-neon laser with a small phase retardation in the cavity, the two split modes are very close to each other whose burned holes are overlapped. Then only one mode oscillates while the other is always in lock-in state due to strong mode competition, which forms hidden frequency split. Meanwhile the spacing between adjacent longitudinal modes deviates from original value and produces a certain variation equal to twice the hidden splitting frequency difference. As a result the longitudinal modes spacing variation is dominated by the phase retardation. On the other hand, by applying transverse magnetic field to a laser tube along the polarization direction, the neon atoms will undergo transverse Zeeman effect and be divided into two groups to provide the gain for polarized light beams parallel to the magnetic field and perpendicular to the magnetic field respectively. Then the laser mode competition is greatly weakened so that the two split modes can oscillate simultaneously to obtain the frequency difference. In order to make profound study of the consistency between longitudinal mode spacing variation and splitting mode frequency difference in the presence of transverse magnetic field, the samples of tilted quartz plate or half wave plate is placed into laser cavity to produce phase retardation. By the two mentioned methods, the splitting frequency difference varying with phase retardation of samples is deduced to make a comparison. Two measurements show that the average relative deviation is less than 1%, while the experimental results accord with theoretical analyses quite well. In this way splitting frequency difference of Zeeman dual-frequency laser can be determined accurately, and a new method to measure the phase retardation of half wave plate is provided.

Laser mode competition effects on output optical pulse high-frequency noise

High-frequency noise in an output optical pulse severely affects amplitude stability and pulse within the high-power acousto-optic Q-switched diode-pumped solid-state laser. In this study, we assessed the output optical pulse via fast Fourier transform (FFT) method under high pump power conditions to find that high-frequency noise in the output optical pulse is chiefly concentrated in the 0.25–1.8 GHz frequency band. High-frequency noise within 0.25–1 GHz and 1–1.8 GHz is mainly caused by high transverse and multi-longitudinal modes in the laser resonator. Our experimental and theoretical analysis results are in close accordance; both indicate that mode competition is the main factor affecting the output optical pulse high-frequency noise.

Self-Induced Second-Harmonic and Sum-Frequency Generation from Interfacial Engineered Er3+/Fe3+ Doped LiNbO3 Single Crystal via Femtosecond Laser Ablation

An interfacial engineered 1 mol % Er3+ and 0.07 mol % Fe3+ doped LiNbO3 single crystal was prepared by processing its surface into periodic rectangular arrays under femtosecond laser ablation. We demonstrated effective self-induced second-harmonic and sum-frequency generation emission peaks at 391, 487, 582, and 762 nm excited by a continuous wave laser at 980 nm, which were accompanied by the typical upconversion spectrum. Significant scattering and localization effects were analyzed as two main factors that contributed to the second-harmonic and sum-frequency generations. In addition to these observations, nanosecond second-harmonic laser emission peaks centered at 534.6 and 532.0 nm with a full width at half-maximum of approximately 0.77 nm were also generated under nanosecond laser illumination at 1064 nm. The obvious laser mode competition between these two emission peaks was investigated, and finally, the peak at 532.0 nm won with the increase of the pumping laser energy. These findings may play a v...

Topologically Controlled Intracavity Laser Modes Based on Pancharatnam-Berry Phase

Incorporation of a metasurface that involves spin-orbit interaction phenomenon into a laser cavity provides a route to the generation of spin-controlled intracavity modes with different topologies. By utilizing the geometric phase, Pancharatnam-Berry phase, we found a spin-enabled self-consistent cavity solution of a Nd:YAG laser with a silicon-based metasurface. Using this solution we generated a laser mode possessing spin-controlled orbital-angular momentum. Moreover, an experimental demonstration of a vectorial vortex is achieved by the coherent superposition of modes with opposite spin and orbital angular momenta. We experimentally achieved a high mode purity of ∼95% due to laser mode competition and purification. The photonic spin-orbit interaction mechanism within a laser-cavity can be implemented with multifunctional shared-aperture nanoantenna arrays to achieve multiple intracavity topologies.

Theoretical study of laser-mode competition in quantum-dot semiconductor lasers using a self-consistent electro-opto-thermal model

We present a new model for quantum-dot (QD) semiconductor lasers which includes the self-consistent treatment of electrical, optical, and thermal interactions. The approach is developed from the energy balance equation to incorporate the carrier temperature and a three-level rate equation to describe the carrier and photon dynamics within the QD active region operating simultaneously on two longitudinal modes: via ground-state (GS) and first-excited-state (ES) transitions. Using the presented model, the steady-state, small-signal modulation response and transient device characteristics are calculated and analyzed. Similar to the situation of mode competition of laser modes, it is found that the light output power of the GS mode enters the roll-off regime, while the power of the ES mode increases. The model also predicts the negative temperature dependency of the power threshold for the ES mode, which can be understood from the negative temperature-dependent behavior of incomplete clamping of the ES population above the GS threshold. The simulated results are in good agreement with experimental data from the devices reported earlier.

Simple tunable dual-wavelength fiber laser and multiple self-mixing interferometry to large step height measurement.

A simple tunable dual-wavelength fiber laser was developed and multiple self-mixing interferometry to large step height measurement was demonstrated. The fiber laser, which can emit two wavelengths without laser mode competition, is composed of a single fiber ring cavity and two fiber branches. Each branch includes a length of erbium-doped fiber and a fiber Bragg grating. Large step heights can be measured using multiple self-mixing interference of the two wavelengths. The maximum height that can be measured is half synthetic wavelength of the two wavelengths. A step height of 2mm constructed with two gauge blocks has been measured. The standard deviation of measurement results is 2.5nm.

Development of dual-wavelength fiber ring laser and its application to step-height measurement using self-mixing interferometry.

A dual-wavelength erbium-doped fiber (EDF) ring laser was developed and its application to step-height measurement using two-wavelength self-mixing interferometry (SMI) was demonstrated. The fiber laser can emit two different wavelengths without any laser mode competition. It is composed of two EDF laser cavities and employs fiber Bragg gratings to determine which wavelengths are emitted. The step heights can be measured using SMI of the two wavelengths, and the maximum height that can be measured is half the synthetic wavelength of the two wavelengths. A step height of 1mm was constructed using two gauge blocks and then measured using the laser. The measurement was repeated ten times, and the standard deviation of the measurements was 2.4nm.

Modeling of laser mode self-adapted filtering by photorefractive Fabry–Perot interferometers

The reduction of the number of oscillating modes by a self-adapted Fabry–Perot (FP) filter was first demonstrated in a dye laser in 1987 [Opt. Lett. 12 (1987) 117]. A renewal of interest in this technique arose recently with the observation of a dramatic reduction of the number of modes in a pulsed Sapphire:Ti laser [Appl. Phys B 69 (1999) 155]. A self-adapted Fabry–Perot filter is made of a photorefractive crystal inserted inside a linear laser cavity between the amplifier and the output coupler. This coupler acts as one mirror of this Fabry–Perot while the Bragg reflection grating recorded by the standing waves inside the crystal plays the role of the second mirror. The dynamic properties of the photorefractive effect make this Fabry–Perot continuously adapted to the oscillating modes. Its spectral reflectivity reinforces the competition between these modes which, in some cases, leads to a single-mode operation. We analyze the laser mode competition taking into account the laser gain properties and the wavelength dependence of the cavity losses induced by the self-adapted Fabry–Perot.

Numerical analysis of laser mode competition and stability

The competition between simultaneously oscillating modes in a laser oscillator is discussed. We analyze numerically the mode completion in a laser with two or three modes that are oscillating over their threshold, starting from the stability conditions in different situations of coupling between modes. For the two-mode oscillating case, our results represented in the intensity–time plane lead to the same conclusions as those from the published literature represented in the intensity–intensity plane.

Longitudinal Mode Competition and Asymmetric Gain Saturation in Semiconductor Injection Lasers. I. Experiment

Longitudinal mode competition in transverse-mode-controlled laser diodes has been experimentally investigated. A careful examination of the output power change associated with both random mode switching and hysteretic mode jumping has revealed a peculiar feature of mode competition in laser diodes; in most devices, the output power is decreased as the lasing mode jumps from a shorter to a longer wavelength mode, which it is increased at mode jumping toward shorter wavelengths. The peculiar feature has been interpreted in terms of an asymmetry in gain saturation, which was experimentally observed. A terminal voltage change associated with mode jumping has also been measured. In some devices, a small shift of the beam profile was observed at mode jumping.

SNR Fluctuation and Nonlinear Distortion in PFM Optical NTSC Video Transmission Systems

The causes of SNR fluctuation and nonlinear distortion, uncovered during field trials of PFM optical video transmission systems, are investigated theoretically and experimentally. Degradations are found to be significant in long distance transmission at a wavelength around 0.85 μm. This is because PFM pulse jitter closely relating to the degradation is caused by laser mode competition and its interaction with fiber material dispersion. However, at a wavelength around 1.3 μm, where fiber material dispersion is negligible, only small nonlinear distortion due to feedback light from connectors is observed. Thus, good picture quality is maintained over long distance transmission.

Mode competition in lasers with homogeneous line broadening

This paper deals with the general concepts of mode interaction in the case of homogeneous line broadening. A simple analysis of rate equations for the radiation fields of the operating modes based on a somewhat phenomenological picture describes the asymptotic values of the mode intensities. Conditions are deduced in which mode interaction leads to the survival of only the most strongly excited mode, although initially all competing modes are above threshold. It is argued that this theory holds for CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> lasers. As examples we calculate competition between 1) the TEM <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</inf> and TEM <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</inf> mode and 2) two rotational transitions.