Fluctuation mechanism of ultrashort pulse generation by laser with saturable absorber

This paper presents a theoretical treatment of the fluctuation mechanism involved in the generation of picosecond laser pulses with saturable absorbers. The processes responsible for the shortening of the pulsewidth and for selection of the most intense pulse are treated. Some experimental results that confirmed the treatment are presented. The influence of inertia of saturable absorber and nonlinear losses (self-focusing and self-modulation) is discussed.     

采用不同可饱和吸收体的Nd：YAG激光器的锁模运转

本文报道采用五甲川染料、Cr^4 ：YAG和LiF:F2分别作为可饱和吸引体实现闪光灯泵浦的Nd:YAG激光器的锁模运转,得到稳定的单脉冲序列。着重分析了Cr^4 :YAG激光态吸收饱和导致的被动锁模以及在LiF:F2^-调Q下Nd:YAG的自聚焦引起的锁模运转机制的锁模过程、理论分析与实验结果一致。     

Femtosecond Cr:forsterite laser with mode locking initiated by aquantum-well saturable absorber

We studied a mode-locked Cr:forsterite laser pumped by a diode pumped Nd:YVO₄ laser. Both the Kerr lens mode locking and the semiconductor saturable absorber initiated mode locking have been demonstrated. Using our measured dispersion data of the forsterite crystal, together with our dispersion compensation technique, we obtained 20-fs pulses for the pure Kerr lens mode locking and 36-fs pulses for semiconductor saturable absorber initiated mode locking, respectively     

Ultra-low repetition rate linear-cavity erbium-doped fibre laser modelocked with semiconductor saturable absorber mirror

Reported is an ultra-long linear-cavity erbium-doped fibre laser modelocked by a high modulation depth hybrid mirror-based semiconductor saturable absorber mirror with ultra-low repetition rate and highlychirped output pulses of high energy. With a repetition rate of 250.7 kHz, the laser delivers the single pulse energy of 14 nJ at a pump power of 430 mW. The minimum achievable repetition rate was as low as 25.4 kHz.     

Propagation of optical pulses in a saturable absorber

The coupled Maxwell-Schrodinger equations are used to describe propagation of a pulse in a nonlinear absorbing medium. The absorber is assumed to be comprised of a homogeneously broadened system of two-level atoms that are exactly resonant with the field. Numerical calculations have been performed for incident pulses of hyperbolic-secant shape and of duration that is long compared to the atomic phase-memory time. Selected values of input intensity are considered. For intensities below a certain level the calculations nearly agree with rate-equation predictions, but as the incident intensity is increased we find that optical nutation comes into play. The nutation effect leads to pulse breakup as the packet penetrates into the medium. An analytical calculation, for the case of an applied optical field of step-function form, has been performed in order to provide additional insight about the intensity threshold for nutation.     

Narrow-linewidth, singlemode erbium-doped fibre laser withintracavity wave mixing in saturable absorber

Narrow-linewidth, single longitudinal mode operation is demonstrated in an erbium-doped fibre laser with an intracavity nonlinear absorptive wave mixing of the counter propagating beams. An unpumped length of erbium-doped fibre serves as the saturable absorber. Linewidths of the order of a few kilohertz are obtained     

Dispersion compensation-free fiber laser mode-locked and stabilized by high-contrast saturable absorber mirror

We report here a compact diode-pumped fiber laser that represents a promising route to designing a portable and rugged picosecond light source. The laser presented in this paper is based on a high-contrast semiconductor saturable absorber mirror (SESAM) and targets reliable picosecond-range sources. The cavity is simple since no dispersion compensators are used, and the SESAM-based mode locking mechanism is robust and self-starting, resulting in low-maintenance turn-key operation. We investigated pulse formation in a short-length fiber cavity and found that nonlinear effects in a near-resonant SESAM in combination with large-cavity dispersion provide the predominant mechanism that causes pulse shaping. The role of a resonant high-contrast SESAM in preventing low-frequency Q-switching instability has been elucidated. The effect of the recovery time of the SESAM on the stretched pulse width and spectrum for resonant-type absorber mirrors was also studied.     

Theory of mode-locked lasers containing a reverse saturable absorber

An analytic solution is presented for mode-locking a laser using a saturable absorber and reverse saturable absorber with long relaxation times compared to the temporal pulse widths. A reverse saturable absorber is a material with an excited-state absorption cross section larger than the ground-state absorption cross section, where increasing the incident light intensity increases the absorption. The reverse saturable absorber plays an important role in mode-locking laser materials where individual pulses cannot saturate the gain. A numerical example of mode-locking a CW alexandrite laser with a reverse saturable absorber and a saturable absorber is presented.     

LD泵浦Nd:YVO4晶体Cr4+:YAG被动调Q激光特性研究

考虑LD泵浦光强和腔内振荡光强的空间高斯分布以及晶体热效应的影响,给出了Nd：YVO4晶体Cr^4 ：YAG被动调Q1．06μm激光的耦合速率方程组,数值求解该方程组获得了输出激光的平均输出功率、脉冲宽度、重复率随泵浦功率的变化特性,其理论值与实验结果相符。     

Passive mode locking in a diode-pumped Nd:GdVO/sub 4/ laser with a semiconductor saturable absorber mirror

We demonstrate Q-switched and CW passive mode locking in a laser-diode-pumped Nd:GdVO/sub 4/ laser with a semiconductor saturable absorber mirror. The repetition rate of the Q-switched envelope increased from 23.1 to 260 kHz as the pump power increased from 1.75 to 13.0 W. At a pump power of 13.7 W, the Q-switched mode locking changed to CW mode locking. The maximum average output power of 4.9 W with a 140-MHz repetition rate was obtained at a pump power of 17.9 W and the single mode-locked pulse energy was 0.035 /spl mu/J. The CW mode-locked pulse duration was measured to be /spl sim/11.5 ps.     

Generation and dynamics of special mode-locked pulses in an ultrafast Er-doped fiber laser with SMF-GIMF-SMF saturable absorber

<正>In this paper, we have demonstrated an Er-doped ultrafast laser with a single mode fiber-gradient index multimode fiber-single mode fiber(SMF-GIMF-SMF, SMS) structure as saturable absorber(SA), which can generate not only stable single-pulse state, but also special mode-locked pulses with the characteristics of high energy and noisy behaviors at proper pump power and cavity polarization state. In addition, we have deeply investigated the real-time spectral evolutions of the mode-locked pulses through the dispersive Fourier transformation(DFT) technique. It can be found that the pulse regime can actually consist of a lot of small noise pulses with randomly varying intensities. We believe that these results will further enrich the nonlinear dynamical processes in the ultrafast lasers.     

Stable single-frequency fiber ring laser for 25-GHz ITU-T grids utilizing saturable absorber filter

A stable single-frequency fiber ring laser is proposed that operates in a single mode for more than an hour by incorporating unpumped erbium-doped fiber (EDF) as a saturable absorber filter and optimizing the length of EDF used as gain medium. This laser can be continuously tuned to 25-GHz spacing that precisely matches the ITU-T grids by temperature control of etalon filter. This laser had a signal-to-source spontaneous emission ratio higher than 70 dB, and lasing frequencies of 361 channels was matched to ITU-T grids with excellent flatness. Frequency offset from the ITU-T grid was less than 0.14 GHz. The linewidth and the relative intensity noise value was less than 1.3 kHz and 130 dB/Hz (above 250 kHz), respectively.     

Tunable dual-wavelength ring fiber laser with stable output based on saturable absorber and thin core passive fiber

A dual-wavelength erbium-doped ring fiber laser is proposed and experimentally demonstrated though a detailed theoretical analysis and experimental verification. The proposed dual-wavelength erbium-doped fiber (EDF) laser, which is based on a ring fiber laser structure, is fabricated using two fiber Bragg gratings. By adjusting the gains and losses of the fiber laser structure, the laser can be switched between single- and double-wavelength modes. A saturable absorber (SA) is used to improve the output laser stability, which is further enhanced by splicing a thin core passive fiber (TCPF) into the laser cavity to produce a Mach–Zehnder filter effect. Optimizing the lengths of the SA and TCPF results in the adoption of a 1-m EDF and a 4-m passive fiber. On the basis of these enhancements and optimizations, a fiber laser with stable output is constructed that incurs single- or dual-wavelength laser shifts of less than 3 pm at room temperature over a period of 250 s.     

Laser mode locking using a saturable absorber incorporating carbon nanotubes

This paper describes a new class of saturable absorber device based on single-wall carbon nanotube (SWNT)-the saturable absorber incorporating nano tube (SAINT). The device possesses ultrafast optical properties comparable to that of the industrial standard semiconductor saturable absorber mirror (SESAM). Passively mode-locked picosecond fiber lasers in different configurations are demonstrated using SAINTs as mode lockers. This is the first demonstration of optical pulsed lasers based on the carbon nanotube technology, and the first practical application of carbon nanotubes in the field of applied optics.     

Topologically multicharged and multihumped rotating solitons in wide-aperture lasers with a saturable absorber

We present results of a semianalytical and numerical study of transverse two-dimensional stationary and oscillating solitons in a wide-aperture laser with a saturable absorber and fast nonlinearity of both gain and absorption. We determine the stability conditions and bifurcations of axially symmetric solitons with screw wavefront dislocations of different order. We demonstrate the existence of asymmetric rotating laser solitons with different numbers of intensity maxima.     

Analysis of wavelength conversion using a multisection DBR laserwith a saturable absorber

The static performance of a wavelength converter obtained by a multisection distributed Bragg reflector (DBR) laser with a saturable absorber between two gain sections is analyzed. For this device an optical input signal at one given wavelength is converted into an output signal at the lasing wavelength. The performances are evaluated in terms of conversion efficiency, suppression ratio, and minimum input power needed for wavelength conversion. It is shown that a proper choice of the injected signal wavelength with respect to the lasing wavelength enhances the conversion efficiency and the suppression ratio and reduces the switching power. The performance can be enhanced also by increasing the electrical current applied to the first gain section provided that the second gain section is biased above the transparency level. The authors have shown that reduction of the front facet reflectivity results in a dramatic increase for the conversion efficiency. The sensitivity to the electrical bias condition and to the resonant condition of the injected signal with respect to the cavity has also been investigated     

Quantum-dot-based saturable absorber with p-n junction for mode-locking of solid-state lasers

We demonstrate stable mode-locking in a Yb : KYW laser by using a quantum-dot (QD) saturable absorber structure that incorporates a p-n junction. A reduction in the output pulse duration was measured when a reverse bias was applied to the QD saturable absorber mirror.     

Cr4+:YAG作饱和吸收体的被动Q开关复合单晶光纤激光器

采用激光加热基座法(LHPG)将Cr4 :YAG单晶光纤和Nd3 :YAG单晶光纤生长为一体化复合单晶光纤。进一步实验研究该单晶光纤的一些性质,表明它满足全固化被动调Q激光器的要求。已实现了脉宽10ns、最大平均输出功率达30mW、重复频率为16kHz的调Q激光。     

230 fs, 25 W pulses from conventional mode-locked laser diodes with saturable absorber created by ion implantation

230 fs, 25 W pulses are obtained from conventional mode-locked AlGaAs laser diodes with highly-reflecting external cavities. Uncoated commercial diodes are used with a region of saturable absorption created by ion implantation. The overall pulse performances are believed to be among the best reported from simple electrically-pumped laser diodes without using additional amplifier sections.<>     

Generation of picosecond blue light pulse by frequency doubling ofgain-switched GaAlAs laser diode having saturable absorber

Picosecond pulse generation of blue light by frequency doubling of a GaAlAs laser diode is reported. High power pulse generation is realized by incorporating gain switching of a laser diode with a saturable absorber and frequency doubling in a proton-exchanged MgO:LiNbO₃ waveguide. The laser diode with a longer saturable absorber can produce optical pulses with higher peak power and narrower pulse width. The spectral bandwidth of second-harmonic generation for the waveguide is evaluated at about 20 nm. This is wide enough to frequency-double all the multilongitudinal modes of the gain-switched laser diode. A blue light pulse of 7.88-mW maximum peak power and 28.7-ps pulsewidth is obtained for a 1.23-W peak pulse of the laser diode