Michelson mode selectors and spatial hole burning in single-mode cw dye lasers

Single-mode selection with Michelson selectors in cw standing-wave dye lasers is analyzed. The application of single and double Michelson mode selectors for compensation of spatial hole burning effects is described in detail. Upper limits for the pumping are considered. It is shown that with spatial hole burning compensation, even the single Michelson selector provides sufficient selectivity for high power single-mode operation in linear cavities.     

A high-power single-mode cw dye ring laser

Due to spatial hole burning, standing-wave dye lasers require a large amount of selectivity inside the cavity for single-mode operation. The output power of these lasers is limited by losses caused by the frequency selecting elements. In a travelling-wave laser, on the other hand, spatial hole burning does not exist, thereby eliminating the need for high selectivity. A travelling-wave cw dye laser was realized by unidirectional operation of a ring laser, yielding single mode output powers of 1.2 W at 595 nm and of 55 mW in the UV-region with intracavity frequency doubling.     

1018 nm短波长掺镱光纤激光高功率自组织相干合成

搭建了两台高功率、低量子损耗的1018 nm短波长掺镱光纤激光器,进行了全光纤结构下两路光纤激光器的相干合成实验。获得了功率为55 W、合成效率为90.2%的相干输出,这是当前严格单模1018 nm光纤激光器的最高功率水平。同时,验证了Michelson腔自组织相干合成技术能够实现光纤激光器的高功率单模输出。     

The conditions for total reflection of low-energy atoms from crystal surfaces

A single-mode dye laser is described in which a “double Michelson” mode selector is used instead of intracavity Fabry-Perot systems. This simple device gives a lower threshold, a high single-mode power (≳250 mW), and a good geometrical quality of the laser beam. Synchronous pressure scanning of the cavity and the mode selector frequencies makes it possible to continuously sweep the optical frequency over 40 GHz without any difficulty. Another version, in which one mirror of the “double Michelson” has been replaced by a retroreflecting optical grating, is also reported. In this case, no selective element (Lyot filter, wedge, ...) has to be inserted in the laser cavity.     

Single mode operation of cw dye lasers

This paper describes an investigation of the special problems of single mode operation in cw dye lasers. Single mode operation in homogeneously broadened lasers can be obtained, if the gain due to spatial hole burning is compensated by dispersive elements, as prisms, Fabry-Pérot etalons and single dielectric interfaces within the resonator. The gain and the influence of the dispersive elements were calculated for two commonly used types of resonators. The calculations make it possible to design simple continuously tunable single-mode systems.     

Proposed enhancement of single mode operation in VCSELs using diffused quantum well structure

The use of interdiffused quantum wells to enhance single transverse mode operation in vertical cavity surface emitting semiconductor lasers is proposed and analysed theoretically. It is found that by introducing a step diffused quantum well structure inside the core region of a quantum-well active layer, the influence of self-focusing (due to carrier spatial hole burning and thermal lensing) on the profile of transverse modes can be minimized. Therefore, stable single-mode operation in vertical cavity surface emitting lasers can be maintained.     

光谱烧孔中孔的宽度和深度与烧孔光持续时间的关系

本文由光学Bloch方程出发,讨论了二能级系统光谱烧孔中孔宽和孔深与烧孔激光脉冲持续时间的关系.在强场下短脉冲烧孔中,用π脉冲可以得到足够深且宽度小于稳态值的孔.弱场下,孔深与烧孔时间成指数关系.Bloch方程的修正对上述两种条件下烧孔行为的描述无明显影响.以二能级系统光谱烧孔为基础,讨论了永久性光谱烧孔和光子选通光谱烧孔中孔的行为.     

Output spectrum of Yb-doped fiber lasers

An analytical model for self phase modulation in Yb-doped fiber laser (YDFL) describing output spectrum and its broadening with increasing power has been developed. Spectral measurements in continuous wave (CW) cladding-pumped YDFL have proved the validity of the model demonstrating hyperbolic secant shape of the spectrum and linear increase of the line width with power in 1-12 W range. At lower powers, spatial hole burning and line self-sweeping effects become important and define the lower limit for the line width.     

A single-mode cw dye laser and the spatial hole burning effect

Single-mode operation of a cw dye laser apparently due to the spatial hole burning effect has been obtained by using a thin metallic absorbing film.     

Continuous-wave mode-locked solid-state lasers with enhanced spatial hole burning

In Part I of this paper [1] experimental results were presented and discussed. In this part, we investigate theoretically the dynamics of end-pumped solid-state lasers due to enhanced spatial hole burning. This becomes possible by a fast numerical implementation of the saturated gain in the presence of strong spatial hole burning that allows to treat the multimode case for an arbitrary pumping level. We find for a wide range of laser parameters that the mode spacing of the cw running modes is essentially determined by the length of the gain medium and only weakly depends on the absorption depth of the pump transition. It is shown that spatial hole burning can lead to a completely flat saturated gain profile over half of the gain bandwidth. In mode-locked lasers, the flat gain due to spatial hole burning results in shorter pulses. But the pulses are neither Gaussian-nor sech-shaped as they are in actively or passively mode-locked lasers without spatial hole burning. Further, we show that soliton-like pulse shaping can be used to restore a transform-limited sech-shaped pulse in an end-pumped solid-state laser while exploiting the full gain bandwidth of the laser material.     

Passive mode locking of thin-disk lasers: effects of spatial hole burning

We recently demonstrated that passive mode locking of a thin-disk Yb:YAG laser is possible and that this concept leads to sources of femtosecond pulses with very high average power. Here we discuss in detail the effect of spatial hole burning on the mode-locking behavior of such lasers. We have developed an efficient numerical model and arrive at quantitative stability criteria which agree well with experimental data. The main result is that stable soliton mode locking can in general be obtained only in a certain range of pulse durations. We use our model to investigate the influence of various cavity parameters and the situation for different gain media. We also consider several methods to reduce the effect of spatial hole burning in order to expand the range of possible pulse durations. Received: 4 September 2000 / Published online: 10 January 2001     

Switchable dual-wavelength polarization-maintaining erbium-doped fiber laser using an optical circulator as the all-reflecting mirror

A simple and effective switchable dual-wavelength polarization-maintaining erbium-doped fiber laser is proposed and demonstrated. Only using a uniform fiber Bragg grating written directly in a segment of the photosensitive and polarization-maintaining erbium-doped fiber as the wavelength selector and an optical circulator as the all-reflecting mirror, a stable simultaneous dual-wavelength oscillation is achieved with a wavelength spacing of 0.364 nm experimentally by exploiting the polarization hole burning effect at room temperature. The output can be switched between single- and dual-wavelength by adjusting the polarization controller. The 3-dB bandwidth and the side mode suppression ratio of the laser’s outputs are measured to be less than 0.01 nm and more than 50 dB. The power fluctuation and wavelength drift are measured to be less than 0.50 dB and 0.020 nm over an hour.     

Stable single-mode vertical-cavity surface-emitting laser with a photoresistive aperture

It is numerically demonstrated that on-axis current channeling through the use of a photoactive layer or layers in vertical-cavity surface-emitting laser cavities counteracts hole burning and allows single-mode operation at high currents. The photoactive layers act as a variable-resistivity screen whose radial aperture is controlled by the light itself. Absorption of a small fraction of the light intensity suffices for significant on-axis current peaking with minimum efficiency loss and optical mode distortion.     

Observation of Antiphase State in a Self-Q-switched Nd,Cr:YAG Laser

We experimentally investigate the antiphase dynamics phenomenon in a self-Q-switched Nd, Cr：YAG laser operating at 946 nm. Due to the effect of spatial hole burning, the Q-switched pulses sequences of one, two and three modes at different pump power are observed. The experimental results show that the pulse sequences display classic antiphase dynamics.     

理论研究电流注入对垂直腔面发射激光器多横模行为的影响

从包含时空变量的速率方程出发,针对弱折射率导引垂直腔面发射激光器(VCSELs),利用空间积分法分析了典型电注入参数对VCSELs多横模行为的影响,在不降低模型准确性的前提下提高了仿真效率。仿真结果表明,注入盘孔径和注入环越小、注入强度越低以及电流扩散越弱时,VCSELs更易实现单横模工作;反之,VCSELs高阶横模开始出现并呈现较强的模式竞争,引发了载流子空间烧孔效应,并导致基模强度降低。进一步得出,在环形注入方式下,高阶模式更容易出现且彼此间的竞争较盘形注入时强。     

Two-wave mixing by means of dynamic Bragg gratings recorded by saturation of absorption in erbium-doped fibers

We present experimental results of two-wave mixing in single-mode Er-doped optical fibers for which dynamic Bragg reflectance gratings are formed as a result of saturation of fiber-optic absorption (i.e., by means of the effect of spatial hole burning). The gratings are probed by the same recording waves at lambda approximately = 1549 nm and are detected as periodic changes of the intensity of light reflected from a Sagnac interferometer (with a piece of the doped fiber included) observed when periodic phase modulation is induced in one of the waves. Both rectangular and sinusoidal modulation were used, which permitted evaluation of the grating recording time (tau(g) approximately = 3 ms for OFS-Fitel EDF-HG980 fiber) and the grating amplitude, which proved to be approximately 6-7 times lower than expected from measurements of saturation of fiber-optic absorption by one wave only.     

Phase-Drift-Suppression in Heterodyne Detection Using Coherent Light Source

The validity of the phase-drift-suppression method (PDSM) using coherent light sources of a single-mode laser diode (LD) or multimode Nd:YAG laser has been experimentally shown. PDSM can enhance the stability of an output signal in heterodyne detection using higher order harmonics. In the Michelson interferometer, the fundamental and second harmonics in heterodyne beat signals were detected by two lock-in amplifiers, and the computed signal intensity (CSI) was obtained in the computer as an output signal. Relations between the stability of CSI and modulation indexes in sinusoidal phase modulations were measured. The CSI stability was enhanced about twice by PDSM using a single-mode laser diode, and from 4 times to 9 times using a multimode laser.     

A comparison of the intensity contours of fringes due to multiple reflection and spatial hole burning in semiclassical theory of laser

A comparison between spatial burning in the semiclassical theory of laser and the intensity contours of the fringes due to multiple reflections in a Fabry-Perot cavity is presented. The concept of spatial hole burning is also used in a quantum well system.     

Linear wavelength sweep of a semiconductor laser and its consequence for dispersion measurements and interference noise in optical fibers

The wavelength shift of a semiconductor laser during triangular pulse modulation has been investigated, using both a Michelson interferometer and direct spectral measurements. This property is used to establish a method for high-resolution dispersion measurements limited to 10 ps, and not affected by material dispersion or detector rise time. A theoretical investigation shows under what conditions the method is equivalent to the standard dispersion measurement setup. The technique is applied to measure polar mode dispersion in single-mode fibers. Examples of polarization noise caused by polarization anisotropy and the variation of source wavelength are presented.     

Linear wavelength sweep of a semiconductor laser and its consequence for dispersion measurements and interference noise in optical fibers

The wavelength shift of a semiconductor laser during triangular pulse modulation has been investigated, using both a Michelson interferometer and direct spectral measurements. This property is used to establish a method for high-resolution dispersion measurements limited to 10 ps, and not affected by material dispersion or detector rise time. A theoretical investigation shows under what conditions the method is equivalent to the standard dispersion measurement setup. The technique is applied to measure polar mode dispersion in single-mode fibers. Examples of polarization noise caused by polarization anisotropy and the variation of source wavelength are presented.