TEM00 Mode Research Articles

Testing the suppression of opto-acoustic parametric interactions using optical feedback control

We report an investigation designed to suppress three-mode opto-acoustic parametric interactions in advanced gravitational-wave detectors, through optical feedback control. In this paper, we present our initial results on the control of parametric instability in a high-finesse Fabry–Pérot cavity using low input laser power. We show that injection of an anti-phase TEM01 mode with appropriate power will optically interfere and suppress the excited high-order mode in the cavity within a few seconds.

Generating Ultrashort Coherent Soft X-Ray Radiation in Storage Rings Using Angular-Modulated Electron Beams

A technique is proposed to generate ultrashort coherent soft x-ray radiation in storage rings using angular-modulated electron beams. In the scheme a laser operating in the TEM01 mode is first used to modulate the angular distribution of the electron beam in an undulator. After passing through a special beam line with nonzero transfer matrix element R54, the angular modulation is converted to density modulation which contains considerable high harmonic components of the laser. It is found that the harmonic number can be 1 or 2 orders of magnitude higher than the standard coherent harmonic generation method which relies on beam energy modulation. The technique has the potential of generating femtosecond coherent soft x-ray radiation directly from an infrared seed laser and may open new research opportunities for ultrafast sciences in storage rings.

Laser assisted emittance exchange: Downsizing the x-ray free electron laser

A technique is proposed to generate electron beam with ultralow transverse emittance through laser assisted transverse-to-longitudinal emittance exchange. In the scheme a laser operating in the TEM10 mode is used to interact with the electron beam in a dispersive region and to initiate the emittance exchange. It is shown that with the proposed technique one can significantly downsize an x-ray free electron laser (FEL), which may greatly extend the availability of these light sources. A hard x-ray FEL operating at 1.5 {angstrom} with a saturation length within 30 meters using a 3.8 GeV electron beam is shown to be practically feasible.

Experimental investigation of displacement measurement with homodyne detection

We report one-dimensional small displacement measurement of TEM00 mode with balanced homodyne detection. The smallest measurable displacement in our experimental setup is 0.3 nm. The conjugate properties of displacement and tilt are tested. Finally we analyze the effect of the deviation of local oscillator beam from TEM10 mode on the displacement measurement result. Experimental results are consistent well with the theoretical analyses.

高重复频率LD端面抽运声光调Q腔内倍频绿光激光器

A high effect green laser is realized by acousto-optic(A-O) Q-switched intracavity frequency doubling Nd∶YVO4 /KTP laser,which is formed with a simple two-mirror line cavity.The TEM00 mode green light power of 999 mW is obtained with 1 608 mW of an input 1 064 nm fundamental pump power at the pulse repetition rate of 40 kHz.The corresponding to optical-optical conversion efficiency is up to 62.1%.The spectral width(full width at half maximum) of green laser is about 0.11 nm or less.±1.2% instabilityof output power is obtained.

A high efficient end-pumped TEM00 laser with pulse repetition rate of 5 kHz

An end-pumped Nd:YVO4 laser fiber-coupled diode was designed. A maximum output power of 4.74 W TEM00 mode CW laser was obtained for a pump power of 10.5 W. The optical efficiency and slope efficiency were measured as 45.1 and 57.8% at 1064 nm, respectively. In Q-switching operation, 4.45 W average power at a pulse repletion rate of 5 kHz was produced, with a stability of pulse peak value <2%.

On the potential energy output of a system transporting the electromagnetic energy by means of microwave beams

It is proposed to use such distribution of the radiated field in a wireless energy transportation system that is similar to the distribution of the modified TEM10 mode generated by a laser. It is shown that, in this case, the product of the aperture efficiencies of radiating and receiving apertures substantially exceeds the value of this parameter corresponding to the uniform and optimum Gaussian field distributions. It is found that, in this case, the potential energy output of the energy transportation system increases approximately by a factor of three and can reach about 15 GW at a wavelength of 5 cm for the antenna and rectenna diameters of 1.0 km and 7.4 km, respectively.

High repetition rate dual-rod acousto-optics Q-switched composite Nd:YVO4 laser

We demonstrate the high-repetition rate acousto-optic Q-switching of a dual-rod Nd:YVO4 laser. Two thermally bonded composite YVO4-Nd:YVO4-YVO4 rod crystals were used as the gain medium to reduce the serious thermal effect. The pump mode and its influence on the laser mode were analyzed, and the effective pump radius was controlled by tuning the spectrum of laser diodes with adjustment on the temperature of laser diodes. Three different configurations of cavity optics were designed and the output performance using these cavities was investigated. In Q-switching operation, 73.2 W TEM00 mode average power at 650 kHz was obtained. The stable Q-switching range was from 80 kHz to 650 kHz with the pulse duration increasing from 17.5 ns to 80 ns. In CW operation, 78 W TEM00 mode and 93 W multi-mode output power was achieved with different cavity designs, corresponding to the optical-optical efficiency of 46.5% and 52.2% respectively.

A birefringence-compensated two-rod Nd:YAG laser operating in TEM00 mode with a CW 61W output power

Two identically pumped Nd:YAG rods with a imaging system and a polarization rotator are used in experiments to achieve a complete birefringence compensation. The measured depolarization ratio is from 1.0 to 2.5%, which increases with the increasing of pump power. With a TEM00-mode operation, the depolarization ratio achieved is less than 1%. A dynamically stable resonator is performed using two flat mirrors and an intra-cavity lens. 61 W linearly polarized output was achieved with a M 2 factor of 1.6, which is the state of the art for a lamp pumped laser.

Diodes-double-end-pumped high efficiency continuous wave 36 W TEM00 mode Nd:GdVO4 laser

A continuous wave (CW), high power, diodes-double-end-pumped TEM00 mode Nd:GdVO4 laser operating at 1063 nm is presented. 36 W TEM00 mode output power has been achieved with a maximum absorbed pump power of 65.4 W, corresponding to an optical-to-optical efficiency of 55%. To the best of our knowledge, this is the highest TEM00 mode output power with single Nd:GdVO4 crystal pumped by two high power fiber-coupled diodes using double-end-pumped configuration. Using the moving knife-edge method, the TEM00 mode beam quality factor is measured to be M2 = 1.77.

A 15.1 W continuous wave TEM00 mode laser using a YVO4/Nd:YVO4 composite crystal

A effective continuous-wave (CW), high power laser generated using a YVO4/Nd:YVO4 composite crystal is presented. 18.8 W output power in multi-mode has been achieved with a maximum absorbed pump power of 31.2 W, corresponding to an optical-to-optical efficiency of 60.26%. In TEM00 mode operation, 15.1 W output power also has been achieved with the maximum absorbed pump power of 31.2 W, corresponding to an optical-to-optical efficiency of 47.69%. With a 200 mm focal-length positive lens and using the moving knife-edge method, the beam quality factor is measured to be M2 = 1.2 for TEM00 mode beam.

Birefringence compensation of two tandem-set Nd:YAG rods with different thermally induced features

How to reduce the thermally induced effects in a solid-state rod is a critical assignment for the applications of high-powered diode-pumped solid-state lasers (DPSSLs). In this paper, we study the birefringence compensation in a solid-state laser system containing two tandem-set Nd:YAG rods with different thermally induced characteristics. By reason of the uneven emission wavelengths of the pump LDs, the thermal focal length of one Nd:YAG rod is about 1.3 times as much as that of the other in our study. Using a 90° quartz rotator and a pair of coupling lenses, we investigated the depolarization dependence on different laser structures. It has been found that the birefringence in two laser rods with such different thermally induced features can be excellently reduced by adopting an optimized lens configuration which is not a traditional telescope image system as usually adopted by many researchers. Both the theoretical analyses and the experimental results have demonstrated the performance of our approach. The conclusions have been thought to be useful for constructing a high-average-power laser oscillator with a near- TEM00 mode.

20 W single longitudinal mode Nd:YVO4 retro-reflection ring laser operated as a self-intersecting master oscillator power amplifier

We demonstrate the stable operation of a 20 W single longitudinal mode TEM00 Nd:YVO4 ring laser at 1064 nm. Unidirectionality of 2500:1 was imposed through retro-reflection of one of the output arms. An additional extra-cavity pass of the intra-cavity gain medium, in a self-intersecting master oscillator power amplifier setup, is shown to improve the stable TEM00 operation power from ≈15 to 20.0 W. The spatial quality improvement involves splitting of the gain region into oscillator and amplifier sections leading to enhanced fundamental mode selection. It is believed that the segregation is, at least in part, self-organising.

High-power non-astigmatic TEM00 and vortex mode generation in a compact bounce laser design

A novel design of a diode-side-pumped bounce amplifier laser is described that can produce a high-power TEM00 mode and Laguerre–Gaussian (LG) vortex mode operation with high circularity and low astigmatism. The design utilises control of pump size and bounce angle such that the laser mode experiences substantially circular symmetric gain and spherical thermal lensing, in a highly compact fundamental mode resonator. In a simple plane–plane Nd:YVO4 laser resonator with no other optical components and total length of just 13.4 cm, highly circularised TEM00 operation is produced at wavelength 1064 nm, with 14.2 W of power and high beam quality M 2<1.05. Stable Q-switched TEM00 operation is demonstrated up to 900 kHz and second harmonic power of 7.2 W at 532 nm is generated with conversion efficiency up to 64%. Minor modification of the design to exploit the spherical aberration of the thermal lens is shown to allow for generation of a doughnut-shaped LG vortex mode with average power 16.6 W, maintaining extremely low astigmatism. Q-switched operation of the vortex mode is accomplished up to 400 kHz. A detailed numerical thermal analysis of the amplifier design is performed and gives quantitative agreement with experimental results.

Prospects of higher-order Laguerre-Gauss modes in future gravitational wave detectors

The application of higher-order Laguerre Gauss (LG) modes in large-scale gravitational wave detectors has recently been proposed. In comparison to the fundamental mode, some higher-order Laguerre Gauss modes can significantly reduce the contribution of coating Brownian noise. Using frequency domain simulations we give a detailed analysis of the longitudinal and angular control signals derived with a LG33 mode in comparison to the fundamental TEM00 mode. The performance regarding interferometric sensing and control of the LG33 mode is found to be similar, if not even better in all aspects of interest. In addition, we evaluate the sensitivity gain of the implementation of LG33 modes into the Advanced Virgo instrument. Our analysis shows that the application of the LG33 mode results in a broadband improvement of the Advanced Virgo sensitivity, increasing the potential detection rate of binary neutron star inspirals by a factor 2.1.

Diffraction losses and selection of transverse modes in complex resonators

Diffraction losses are estimated for TEM00, TEM01, and TEM10 modes which can be generated in complex resonators. Dependences of the output power of the laser operating in the regime of transverse oscillation suppression on the transmission of the mirror are obtained. Optimal relationships between the field stop aperture area and the optical beam cross section are determined as functions of the gain of the active medium.

Analytical non-paraxial TM polarized Gaussian beam in the source region

The non-paraxial TM polarized Gaussian beam, which approximately reduces to be a Gaussian TEM00 mode at the paraxial case, is the rigorous solution of Maxwell's equations for a confocal resonator. By means of mathematical techniques, the analytical expression in the source region has been derived without any approximation and expressed as a sum of the propagating part and the evanescent part. With some certain given values of the initial Gaussian half width w 0, the distributions of the squared modulus of the propagating part, the evanescent part, and the whole beam are depicted in the reference plane close to the source. When w 0 is small enough, the squared modulus of the non-paraxial TM polarized Gaussian beam is composed of two lobes, which results from the contribution of the evanescent wave. This research further reveals the difference of a non-paraxial TM polarized Gaussian beam from a non-paraxial Gaussian beam.

183 WTEM00 mode acoustic-optic Q-switched MOPA laser at 850 kHz

We report a high-power, high-repetition-rate TEM00 mode MOPA laser using acoustic-optic Q-switching. Seed laser from the dual-end- pumped Nd:YVO4 oscillator was scaled up to 183.5 W average power at 850 kHz after behind amplified by the four-stage power amplifiers. The stable Q-switching operation worked at different pulse repetition rate from 60 kHz to 850 kHz while the pulse duration increased from 12.8 ns to 72 ns. The beam quality was near diffraction-limit with M2 factors measured as M2x = 1.28 and M2y = 1.21. In CW operation, 195 W TEM00 mode output was achieved corresponding to the total optical-optical efficiency of 44.7% and the absorbed pump power to output power efficiency of 53.3% respectively.

Measurement and analysis of the characteristics of transverse modes of a sealed-off He-N2-CO2 laser

The characteristics of the transverse modes of a sealed-off He-N2-CO2 laser are measured on-line by using a laser beam analyzer. The influence of the transverse modes on discharge current is observed. It is shown that this laser tube can easily operate on lower order modes under optimum discharge current，but hardly operate on the TEM00 mode. Under the condition of improved symmetry of laser tube and increasing the speed of cooling water, the laser can operate on the TEM00 mode. The variety of laser modes is analyzed through the kinetic process theoretically, which is helpful to the control and improvement of laser mode for high power lasers.

Diode-pumped self-Q-switched Cr,Nd:YAG laser with 7-W average output power

We report a diode-pumped self-Q-switched 1064-nm Cr,Nd:YAG laser with pulse duration in the range of 16?18 ns. The maximum average output power up to 7 W, corresponding to a slope efficiency of 33%, is obtained in a simple and compact linear cavity by using a plane-concave output coupler with a transmittance of 15%. The laser operates at TEM00 mode with a pump power of 14.2 W.