Gaussian Reflectivity Mirrors Research Articles

Double-pass pumping KTA OPO based on unstable resonator with Gaussian reflectivity mirror

A novel double-pass pumping optical parametric oscillator (OPO) with unstable resonator based on Gaussian reflectivity mirror (GRM) was proposed and demonstrated. The output characteristics of double-pass pumping OPO based on non-critical phase matching (NCPM) KTiOAsO4 (KTA) crystal were researched at a pulse repetition frequency of 100 Hz. Compared with the single-pass pumping OPO, the output energy and the conversion efficiency of double-pass pumping OPO were improved by 36 %. The beam qualities of signal and idler were measured and compared with different pump structures, and the results show that beam quality of signal for double-pass pumping OPO barely deteriorated. In addition, the pulse widths of signal and idler under two pumping structures and their variation trends with different pump energies were researched and compared.

Comparison of a high-power 3.75 µm BaGa4Se7 OPO based on a plane-parallel resonator and an unstable resonator with a Gaussian reflectivity mirror.

Using a homemade Nd:YAG laser with a pulse repetition frequency of 300 Hz as a pump source, we demonstrated a tunable BaGa4Se7 (BGSe) optical parametric oscillator (OPO). Wavelength-tuning ranges of 1.42-1.59 µm and 3.21-4.22 µm were realized, and a maximum average output power of 1.03 W at 3746 nm was achieved in a plane-parallel resonator. To date, this is the highest output power at around 4 µm obtained from a BGSe OPO pumped by a 1 µm laser, to our knowledge. Moreover, the BGSe OPO employing a plano-convex Gaussian reflectivity mirror (GRM) as an output coupler (OC) was demonstrated for the first time, to our knowledge. At the same pump power, the corresponding output power and M2 value of the idler at 3746 nm were 0.86 W and 10.2 (x direction) and 11.6 (y direction), respectively. The results indicate that the beam quality factor M2 of the idler has an over 30% improvement in comparison with the BGSe OPO based on a conventional flat OC of a plane-parallel resonator. Limited by the beam quality of the pump source, there is little room for improvement in the beam quality of the BGSe OPO with a GRM OC, which could be improved in the future by optimizing the pump beam.

Investigations on beam quality improvement of an NCPM-KTA-based high energy optical parametric oscillator using an unstable resonator with a Gaussian reflectivity mirror [Invited

Investigations on beam quality improvement of an NCPM-KTA-based high energy optical parametric oscillator using an unstable resonator with a Gaussian reflectivity mirror [Invited

圆形高斯镜平凹腔腔镜倾斜时光场模式分析

By means of boundary finite-element method,the field distributions and eigenvalues of the fundamental mode of the plano-concave resonator with a tilted Gaussian-reflectivity plane mirror are calculated and discussed.The results show that the laser mode moves along the direction of the mirror tilting.When the tilt angle of the mirror is big enough,the mode is distorted,no longer with a Laguerre-Gaussian distribution.Furthermore,following the increasing of the tilt angle,the far field distributions become bad,and the eigenvalue decrease.By decreasing the characteristic radius of the Gaussian-reflectivity,the distortion of the mode that is induced by the mirror tilting is decreased.

圆形高斯镜平凹腔腔镜倾斜时光场模式分析

圆形高斯镜平凹腔腔镜倾斜时光场模式分析

Gaussian-reflectivity mirror resonator for a high-power transverse-flow CO_2 laser

A Gaussian-reflectivity mirror resonator is proposed to achieve high-quality laser beams. To analyze the laser fields in a Gaussian-reflectivity mirror resonator, the diffraction integral equations of a Gaussian-reflectivity mirror resonator are converted to the finite-sum matrix equations. Consequently, according to the Fox-Li laser self-reproducing principle, we describe the mode fields and their losses in the proposed resonator as eigenvectors and eigenvalues of a transfer matrix. The conclusion can be drawn from the numerical results that, if a Gaussian-reflectivity mirror is adopted for a plano-concave resonator, a fundamental mode can easily be obtained from a transverse-flow CO2 laser and high-quality laser beams can be expected.

Theoretical models and analytic expressions for buildup time of pulsed confocal unstable optical parametric oscillators with uniform or Gaussian reflectivity mirrors

A theoretical model and a simplified analytic expression are developed to describe the buildup time of a pulsed confocal unstable optical parametric oscillator (OPO) with a uniform-reflectivity mirror (URM) or a Gaussian-reflectivity mirror (GRM). Two analytic expressions have been demonstrated to correspond to theoretical models with a sufficient degree of accuracy. The effects of a variety of cavity and pump parameters on the buildup time of an OPO were investigated and analyzed. It was found that a GRM unstable OPO generally exhibits a shorter buildup time than the corresponding URM unstable OPO with equally effective output coupling.

GRM(Gaussian Reflectivity Mirror)을 이용한 불안정 공진기형 Q-스위치 Nd:YAG 레이저의 출력특성

출력거울로 GRM(Gaussian reflectivity mirror)을 채택한 불안정 공진기를 구성하여 그 Q-스위치 출력의 특성을 분석하였다. 입력 전기에너지가 55J 일 때 1064 nm의 기본파장에서 470 mJ, 532 nm의 제2고조파 파장에서 280 mJ의 출력 에너지를 얻었다. 출력빔의 발산각은 1.7 mrad 이었으며 근접장 영역에서 Top-Hat 형태의 빔을 얻을 수 있었다. We investigated the operational characteristics of a Q-switched Nd:YAG laser, which has an unstable resonator with a GRM(Gaussian reflectivity mirror). With electrical input energy of 55 J, we obtained the fundamental energy of 470 mJ at 1064 nm and the frequency doubled energy of 280 mJ at 532 nm. The Top-Hat profile of the output beam was obtained at the near field, and beam divergence was 1.7 mard.

Low threshold characteristic of pulsed confocal unstable optical parametric oscillators with Gaussian reflectivity mirrors

An iterative threshold model for a pulsed singly resonant Gaussian-reflectivity-mirror (GRM) confocal unstable optical parametric oscillator (OPO) has been proposed. It is found that OPO threshold is determined by important parameters such as GRM central reflectance, Gaussian reflectivity profile, cavity magnification factor, cavity physical length, crystal length, pump pulsewidth. It is demonstrated that this model can be extended to plane-parallel resonator or uniform-reflectivity-mirror (URM) unstable resonator when some specific values are taken. Experimental results show excellent agreement with values calculated from theoretical model. Both theoretical calculations and experimental data illustrate that GRM is a useful solution to reduce threshold of unstable OPO.

Optical beam propagation in gain media written in terms of complex-order Fourier transforms

The optical beam propagation in gain media is represented in terms of fractional-order Fourier transforms. It is shown that in a uniform amplifying medium characterized by a linear gain there exists a complex-order Fourier transform between the fields on two ‘complex-spherical’ reference surfaces of the given radii and separation. Analytical expressions for the transform order and scale factors are derived and, as an application example, the resonator with Gaussian reflectivity mirrors and linear gain medium is illustrated.

Propagation and focusing of Gaussian beams generated by Gaussian mirror resonators.

The propagation and focusing properties of a class of Gaussian beams generated by optical resonators with Gaussian reflectivity mirrors are investigated. Attention is concentrated on the following two beams in this class: (a) the annular Gaussian beam (the Gaussian doughnut mode) and (b) the flat-topped Gaussian beam. A class of flat-topped Gaussian beams is introduced. All analysis is limited to a coherent superposition scheme of the lowest-order Gaussian modes (TEM00) that have different parameters.

Evolution of the beam quality factor for various active medium positions within a Gaussian cavity

A 2-m-long plane-parallel cavity with a Gaussian reflectivity mirror has been applied to a XeCl discharge chamber with a 35-cm-long active medium and the temporal evolution of the main parameters of the intracavity laser radiation after reflection on the Gaussian mirror, has been analysed for various active medium positions within the cavity. It is shown that in cavities of equal length and effective Fresnel number, the properties of the intracavity radiation are dependent on the Gaussian mirror distance from the active medium, since the onset of laser action. Indeed, it has been found that the beam quality factor M 2 reaches smaller values by setting the Gaussian mirror closer to the active medium. It is also shown that a theory formerly developed for the evolution of the parameters of Schell–Gauss model beams propagating in Gaussian-mirror cavities provides a satisfactory description of experimental results.

Coherence temporal evolution in Gaussian cavities of different lengths

The temporal evolution of the beam-quality factor M2 is investigated in plane-parallel cavities of different Fresnel numbers with a Gaussian reflectivity mirror and applied to a Xe–Cl excimer laser. The Fresnel number is changed by varying resonator length. Laser radiation of higher spatial coherence is provided by the cavity of greater length (2.5 m) and then of lower Fresnel number after the first transit. Indeed, the beam spatial coherence decreases with cavity length. It is also shown that the Gaussian mirror affects the properties of the oscillating laser radiation only at the very first cavity round trips. The near- and far-field spatial characteristics of the laser radiation do not vary after a few transits inside the cavity. Experimental results are supported by a theory formerly developed for the evolution of the parameters of Gaussian Schell-model beams propagating in Gaussian cavities.

Parameters evolution of laser beams with quite general transverse intensity profile

A plane-parallel cavity with a Gaussian reflectivity mirror has been applied to a XeCl laser medium having a spatially variable gain distribution. The evolution of the beam parameters has been experimentally analyzed as a function of the number of round trips. It is shown that in this case of intensity profiles affected by the spatial and temporal properties of the active medium gain, a theory formerly developed for the beam-parameter evolution of Gaussian Schell-model beams provides a satisfactory description of experimental measurements for the first few round trips.

Coherence growth of laser radiation in Gaussian cavities

The beam quality and coherence growth of the laser radiation in stable and unstable cavities equipped with a Gaussian reflectivity mirror as output coupler has been investigated. An experimental analysis of the time evolution of the near- and far-field beam quality factor and spot size in dependence on the cavity configuration has been carried out. A theoretical analysis of the time evolution of a Schell-Gauss model beam propagating through Gaussian cavities is seen to provide a satisfactory description of the process in agreement with the experimental measurements for all the tested resonators.

Mode-medium instability and its correction with a Gaussian-reflectivity mirror

A high-power CO(2) laser beam is known to deteriorate after a few microseconds because of a mode-medium instability (MMI) that results from an intensity-dependent heating rate that is related to the vibrationalto-translational decay of the upper and lower CO(2) lasing levels. An iterative numerical technique has been developed to model the time evolution of the beam as it is affected by the MMI. The technique is used to study the MMI in an unstable CO(2) resonator with a hard-edge output mirror for different parameters, e.g., the Fresnel number and the gas density. The results show that the mode of the hard-edge unstable resonator deteriorates because of the diffraction ripples in the mode. We use a Gaussian-reflectivity mirror to correct the MMI. This mirror produces a smoother intensity profile, which significantly reduces the effects of the MMI. Quantitative results on the peak density variation and beam quality are presented.

High-order transverse modes of misaligned laser resonators with Gaussian reflectivity mirrors

Analytical expressions of high-order transverse modes of misaligned laser resonators with Gaussian reflectivity mirrors are presented. We found that modal discrimination is independent of the mirror tilt angle. The propagation laws of the beam parameters are also discussed.

Gaussian reflectivity mirror with an absorbing lens

A simple method for the generation of a Gaussian reflectivity mirror by using an absorbing lens is reported. The efficiency of an unstable resonator using such a Gaussian mirror as the output coupler has been analyzed.

Focusing Properties of the Gaussian Beam Generated by Optical Resonators with Gaussian Reflectivity Mirrors

Abstract This paper presents a parametric study concerning the focusing properties of the light beam generated by optical resonators with Gaussian reflectivity mirrors. The diffraction integral has been evaluated and analytical expressions are derived for intensity patterns near the focus in systems of different Fresnel numbers. Universal curves have been plotted against dimensionless parameters to show the variations in the intensity patterns due to the change in focusing geometry and the incident beam intensity profile. Modification to the well known diffraction formula are considered in order to extend the conventional Gaussian formalism to the case of Gaussian mirror resonators.

Laser mode control with variable reflectivity mirrors

Global efficiency, transverse mode discrimination, and the near- and far-field optical quality of unstable laser resonators are improved with variable reflectivity mirrors (VRMs). Analytical and numerical results are given for Gaussian and parabolic reflectivity mirrors. The VRM design is described, and experimental results obtained using different lasers with Cassegrain cavities are presented.