Matrix formalism for dispersive laser cavities

A matrix formalism for dispersive optical elements is applied to the study of laser cavities with dispersive elements such as gratings or prisms. The formalism consists of 3×3 matrices describing each element with complex coefficients to account for loss or gain. It is shown how to determine the frequency dependence of the beam center, propagation angle, gain, and transit time delay. In this manner, the linewidth selectivity, cavity group velocity dispersion, output spectral angular dispersion, and transverse walkoff of any arbitrary design can be determined     

Blumlein放电长脉冲XeCl激光器的窄线宽输出

本文在一台长脉冲Blumlein放电XeCl准分子激光器上采用光栅、棱镜和标准具等腔内选择元件,研究了XeCl激光器的调谐特性、谱线宽度和光束发散特性。得到了单脉冲能量2mJ、窄线宽(～10~(-2))和衍射极限发散角(0.15mrad)的激光输出。     

Characteristics of a grating-external-cavity semiconductor lasercontaining intracavity prism beam expanders

A grating tuned external cavity semiconductor laser incorporating a gradient-index rod lens and a pair of intracavity silicon prism beam expanders was constructed using a configuration aimed at simultaneously achieving the following objectives: the ability to operate at any external cavity longitudinal mode without tuning gaps caused by residual resonances of the laser diode cavity, stable feedback coupling between the diode and external cavities, narrow optical linewidth, and a high degree of external cavity longitudinal sidemode suppression     

Tunable,Grating-Gated,Graphene-On-Polyimide Terahertz Modulators

An electrically switchable graphene terahertz (THz) modulator with a tunable-by-design optical bandwidth is presented and it is exploited to compensate the cavity dispersion of a quantum cascade laser (QCL). Electrostatic gating is achieved by a metal grating used as a gate electrode, with an HfO₂/AlO_x gate dielectric on top. This is patterned on a polyimide layer, which acts as a quarter wave resonance cavity, coupled with an Au reflector underneath. The authors achieve 90% modulation depth of the intensity, combined with a 20 kHz electrical bandwidth in the 1.9–2.7 THz range. The modulator is then integrated with a multimode THz QCL. By adjusting the modulator operational bandwidth, the authors demonstrate that the graphene modulator can partially compensate the QCL cavity dispersion, resulting in an integrated laser behaving as a stable frequency comb over 35% of the operational range, with 98 equidistant optical modes and a spectral coverage ~1.2 THz. This paves the way for applications in the terahertz, such as tunable transformation-optics devices, active photonic components, adaptive and quantum optics, and metrological tools for spectroscopy at THz frequencies.     

Measurement of the linewidth enhancement factor of semiconductor lasers based on the optical feedback self-mixing effect

A new method for the measurement of the linewidth enhancement factor of semiconductor lasers is presented, based on the interferometric self-mixing effect. It is a fast and easy to perform method that does not require radio frequency nor optical spectrum measurements. A small fraction of the emitted light is backreflected into the laser cavity by a remote target driven by a sine waveform. The mixing of the returned and the lasing fields generates a modulation of the optical output power in the form of an interferometric waveform, with a shape that depends on the optical feedback strength and the linewidth enhancement factor /spl alpha/, according to the well-known Lang-Kobayashi theory. We show that the value of /spl alpha/ can be retrieved from a simple measurement of two characteristic time intervals of the interferometric waveform. Experimental results obtained on different laser diodes show an accuracy of /spl plusmn/6.5%.     

Theoretical stability analysis of single-mode operation inuncontrolled mode-selection semiconductor lasers

An uncontrolled mode-selection laser is a laser containing an intracavity filter under which the cavity mode alignment is uncontrolled. We present a theoretical stability analysis of the single-mode operation of uncontrolled mode-selection semiconductor lasers. We find that to maximize the stability the cavity length and intracavity filter bandwidth must be minimized, and a specific, nonzero, linewidth enhancement parameter must be chosen. For a given cavity mode spacing to filter bandwidth ratio, a shorter cavity is more stable     

Feedback effects at stable and unstable resonant external cavity lengths

External feedback applied to a high-power semiconductor laser is found to be responsible for a drop in output power and an increased noise-level when the optical external cavity length is an integral multiple of the optical internal cavity length. The power drops and extra noise originates from a scan of the quasi-single-mode laser over its internal cavity modes, caused by a lack of interferometric stability. In the case of interferometric stability, the wavelength of the laser exhibits a staircase-like dependence on the external cavity length. All experimental results can be described by a simple rate equation model.     

Theory of spontaneous emission noise in open resonators and its application to lasers and optical amplifiers

A theory of spontaneous emission noise is presented based on classical electromagnetic theory. Unlike conventional theories of laser noise, this presentation is valid for open resonators. A local Langevin force is added to the wave equation to account for spontaneous emission. A general expression is found relating the diffusion coefficient of this force to the imaginary part of the dielectric function. The fields of lasers and amplifiers are found by solving the wave equation by the Green's function method. The lasing mode is a resonant state associated with a pole in Green's function. In this way, noise in lasers and amplifiers is treated by a unified approach that is valid for either gain guiding or index guiding. The Langevin rate equations for the laser are derived. The theory is illustrated with applications to traveling wave and Fabry-Perot amplifiers and Fabry-Perot lasers. Several new results are found: optical amplifier noise increases inversely with quantum efficiency; spontaneous emission into the lasing mode is enhanced in lasers with low facet reflectivities; and the linewidth of a Fabry-Perot laser with a passive section decreases as the square of the fraction of the cavity optical length that is active.     

On the physics of semiconductor quantum dots for applications in lasers and quantum optics

The progression of carrier confinement from quantum wells to quantum dots has received considerable interests because of the potential to improve the semiconductor laser performance at the underlying physics level and to explore quantum optical phenomena in semiconductors. Associated with the transition from quantum wells to quantum dots is a switch from a solid-state-like quasi-continuous density of states to an atom-like system with discrete states. As discussed in this paper, the transition changes the role of the carrier interaction processes that directly influence optical properties. Our goals in this review are two-fold. One is to identify and describe the physics that allows new applications and determines intrinsic limitations for applications in light emitters. We will analyze the use of quantum dots in conventional laser devices and in microcavity emitters, where cavity quantum electrodynamics can alter spontaneous emission and generate nonclassical light for applications in quantum information technologies. A second goal is to promote a new connection between physics and technology. This paper demonstrates how a first-principles theory may be applied to guide important technological decisions by predicting the performances of various active materials under a broad set of experimental conditions.     

半导体激光器参数估计的改进算法

为了精确估计带外腔半导体激光器的线宽展宽因数,采用了光反馈自混合技术和梯度最优算法,可以达到数据—理论的最佳拟合,同时提出了改进的梯度迭代公式,并在参数迭代时引入可变步长,取得了仿真和实验数据,该算法不仅测量精度较高,而且抗噪声性能较好,仿真结果表明当信噪比大于20分贝时,线宽展宽因数的相对标准差小于2.55% ,实验数据处理结果表明线宽展宽因数的相对标准差小于5.1%,这对半导体激光器的应用是有帮助的。     

碰撞锁模染料激光器中激光脉冲的啁啾特性及其色散补偿

从实验上研究了碰撞锁模染料激光器中激光脉冲的啁啾性质.分析了采用两块棱镜组成的棱镜对进行内腔补偿时,棱镜对的色散对输出激光脉冲的宽度、稳定性及光谱特性的影响.     

Laser-controlled optics using near-resonance nonlinear dispersion in gaseous media

Nonlinear dispersion in gaseous media is analyzed from the standpoint of its potential applications to laser-controlled optics. Refractive optics as well as real-time holographic optics are considered. The nonlinear refractive index for a gaseous medium is calculated for near-resonance conditions using the density-matrix formalism, including gaseous collisions. A coupled-wave theory is used to analyze interaction in a laser-controlled, real-time holographic grating. It is shown that the collision-dominated, rather than the collision-free regime, is the more useful for laser-controlled optics applications. The effect of diffusion in the gaseous medium is incorporated in the analysis. Expressions for intensity requirements are derived for laser-controlled holographic optical applications as well as for refractive-optics applications.     

Skin optics

Quantitative dosimetry in the treatment of skin disorders with (laser) light requires information on propagation of light in the skin related to the optical properties of the individual skin layers. This involves the solution of the integro-differential equation of radiative transfer in a model representing skin geometry, as well as experimental methods to determine the optical properties of each skin layer. These activities are unified under the name skin optics. This paper first reviews the current status of tissue optics, distinguishing between the cases of: dominant absorption, dominant scattering, and scattering about equal to absorption. Then, previously published data as well as some current unpublished data on (human) stratum corneum, epidermis and dermis, have been collected and/or (re)analyzed in terms of absorption coefficient, scattering coefficient, and anisotropy factor of scattering. The results are that the individual skin layers show strongly forward scattering (anisotropy factors between 0.7 and 0.9). The absorption and scattering data show that for all wavelengths considered scattering is much more important than absorption. Under such circumstances, solutions to the transport equation for a multilayer skin model and finite beam laser irradiation are currently not yet available. Hence, any quantitative dosimetry for skin treated with (laser) light is currently lacking.     

采用色散型布儒斯特棱镜扩束器和光栅调谐的高效率脉冲钛宝石激光器

详细推导了采用色散型布儒斯特扩束器加光栅调谐脉冲钛宝石激光器压窄线宽的原理，纠正了原有理论的错误之处，实验结果和理论结果相吻合。该系统具有较宽的连续调谐范围和较窄的线宽，并获得较高的窄线宽运转的激光效率。     

The results of lasing linewidth narrowing on VEPP-3 storage ringoptical klystron

Lasing in the visible and ultraviolet ranges was reached in the optical klystron installed on a VEPP-3 storage ring (see N. A. Vinokurov et al., 1977) with minimum relative linewidth Δλ/λ = 10^-4. In order to decrease the linewidth the authors performed the experiments reported here. The optical cavity on VEPP-3 storage ring optical klystron was updated to install intracavity selective elements. The authors used the simplest selective element-a glass plate with parallel planes as a natural interferometer. With a 1.2 mm thick glass plate installed inside the optical cavity, lasing has been reached with a very narrow linewidth. The minimum relative lasing linewidth, 2.7×10^-6 (λ=6250 Å, Δλ=0.017 Å), was 30 times narrower than the minimum one without the plate (Δλ=0.6 Å). The average power was the same in both cases     

Dye-laser cavity employing a reflective beam expander

A repetitively pulsed dye laser employing a reflective intracavity beam expander achieves a 50-MHz full width at half-maximum (FWHM) linewidth. A geometrical technique for partially correcting the expander astigmatism and maintaining cavity stability is derived. The use of reflective cavity elements minimizes cavity losses and eliminates spurious reflections.     

Semiconductor laser stabilization by external optical feedback

A report is presented on a general theory describing the effect of external optical feedback on the steady-state noise characteristics of single-mode semiconductor lasers. The theory is valid for arbitrarily strong feedback and arbitrary optical feedback configuration and spectrum. A generalized Langevin rate equation is derived. The equation is, in general, infinite order in d/dt constituting an infinite-order correction to the low-frequency weak-feedback analysis. The general formalism includes relaxation oscillations and permits analysis of the effect of feedback on the laser linewidth, frequency noise, relative intensity noise, and the relaxation oscillation sidebands in the field spectrum. The theory is applied to two important feedback configurations: the laser coupled to a single mirror and the laser coupled to a high-Q cavity     

Dynamic spectral broadening in digitally modulated lasers

It is demonstrated that Gbit/s digitally modulated, voltage controlled singlemode multiple quantum well semiconductor lasers with an intracavity saturable absorber show reduced spectral broadening compared to conventional high contrast modulation schemes. The intracavity loss modulated laser linewidth is also calculated using experimentally determined voltage and intensity dependence of absorption in MQW modulators and excellent agreement with experiment is found.<>     

自适应光学对星地相干激光通信性能改善研究

相干激光通信能够实现每秒数百吉比特的通信速率和接近量子极限的灵敏度,在未来天地一体化信息网络中具有广泛的应用前景。大气湍流引入的光学波前畸变是影响星地相干激光通信链路性能的重要因素。本文将自适应光学技术应用于大口径光学地面接收站,并系统地开展了4 Gbps高速相干激光通信试验,试验结果表明,自适应光学技术能够有效抑制中等大气湍流的影响,并提高相干激光通信的灵敏度和稳定性。