Mode-locking Of Nd Research Articles

Nonlinear Optical Response of the Colloidal CdSe Nanoplatelets under One-Photon Stationary Excitons Excitation

Nonlinear change in transmission and photoluminescence of the colloidal CdSe nanoplatelets in the case of stationary exciton excitation by the third harmonic of mode-locked Nd3+:YAP laser pulses allowed to identify peculiarities of the exciton dynamics. The values of saturation intensity were determined from the measured differential transmission spectra. The revealed broadening and red shift of the photoluminescence spectra can be the evidence of the formation of trions and their radiative recombination at room temperature.

Dynamical equations of intra-cavity optical parametric oscillator synchronously pumped by SESAM mode-locked laser

By considering the intensity fluctuation mechanism of the fundamental laser, the rate-equation-based model for the CW mode-locking intra-cavity OPO (IOPO) is developed, which includes the behavior of the fundamental laser, the signal and idle light. In the derived model, the OPO nonlinear conversion is considered as a loss for the fundamental laser and thus the mode-locked signal or idle profile originates from the mode-locked fundamental laser. In experiment, the CW mode-locked Nd3+: GdVO4/KTA IOPO with semiconductor saturable absorber mirror (SESAM) is realized. The near-infrared signal light is obtained, which are generated from the IOPO pumped by CW mode-locked fundamental laser. The signal and fundamental spectra are experimentally measured, and then the wavelength of the idle light is estimated to be 3.31 μm. The theoretical values from the rate equations agree with the experimental results well. The developed model explains the behavior of the mode-locked IOPO, which is helpful to system optimization.

Passively mode-locked Nd^3+:YVO_4 laser using a molybdenum disulfide as saturable absorber

A molybdenum disulfide (MoS2) saturable absorber (SA) was fabricated by vacuum filtration method and employed to achieve passively mode-locked Nd3+:YVO4 laser. The optical properties of MoS2 were systematically characterized and the modulation depth was measured to be 7%. Stable continuous-wave mode-locked (CWML) laser at 1064.2 nm was realized with a pulse repetition frequency of 88.3 MHz and a pulse width of 12.7 ps. The maximum output power of 89 mW was obtained under an incident pump power of 2.1 W. The single pulse energy and peak power were calculated to be 1.0 nJ and 83.3 W, respectively.

Two-Photon Excited Diffraction Grating: Self-Diffraction and Nonlinear Optical Properties of Colloidal CdSe/ZnS QDs

Specific features have been revealed of nonlinear optical processes occurring when the total energy of two photons of a mode-locked Nd3+:YAG laser coincides with the energy of the main electron—hole (exciton) transition in colloidal CdSe/ZnS QDs and the effective self-diffraction of two laser beams arises on the induced diffraction grating.

Neodymium laser with negative feedback: Suppression of self-mode-locking, control of mode-locking regime

A simple way of suppression of self-mode-locking in a nanosecond Q-switched Nd3+:YAlO3 laser by placing an element introducing a negative feedback into the laser cavity, which consists of a plate of singlecrystal GaAs exhibiting two-photon absorption (complete suppression) or a cell containing colloidal solution of CdSe/ZnS quantum dots (partial suppression), is implemented. Placing the element introducing the negative feedback into the cavity of a pulsed picosecond mode-locked Nd3+:Y3Al5O12 laser allowed an increase in the number of pulses in the pulse train and a change in the energy distribution between the pulses. Specificities of laser oscillation regimes in the presence of a nonlinear absorbing element in the cavity were analyzed by numerically solving the set of balance equations describing the population inversion density and the photon flux density in the cavity.

Passive mode-locking of diode-pumped Nd:GdVO4 laser with carbon nanotube intracavity absorber

By using single-walled carbon nanotubes as the saturable absorber fabricated by a vertical evaporation method, passive mode-locking of a Nd:GdVO4 laser was realized in a W-type folded cavity. The laser generated 8 ps pulses at a repetition rate of 81 MHz. At 10.4 W of the incident pump power, average output power of 1.22 W was achieved and the corresponding peak power and energy of a single pulse were 1.88 kW and 15 nJ, respectively.

Dual-wavelength asynchronous and synchronous mode-locking operation by a Nd:CLTGG disordered crystal

We have developed a diode-pumped passively mode-locked Nd3+:CLTGG laser operated at 1059 and 1061 nm with a semiconductor saturable absorber mirror (SESAM). The relative intensity of the two spectrum wavelengths is adjustable, allowing asynchronous and synchronous generation of the dual-wavelength pulses. In synchronous mode-locking regime, a total average output power of 383 mW was obtained with pulse duration of 3.5 ps and repetition rate of 42 MHz. The two spectral bands of 1059 and 1061 nm had the same intensities and areas, indicating 1:1 for the pulse energy ratio. It is desirable for efficiently generating a terahertz wave by difference-frequency generation.

自聚焦透镜耦合激光二极管抽运Nd:YVO4锁模激光器的研究

自聚焦透镜耦合激光二极管抽运Nd:YVO₄锁模激光器的研究

Passive mode-locking of a diode-pumped Nd:YVO_4 laser by intracavity SHG in PPKTP

Experimental results on passive mode-locking of a Nd:YVO(4) laser using intracavity frequency doubling in periodically poled KTP (PPKTP) crystal are reported. Both, negative cascaded chi((2)) lensing and frequency doubling nonlinear mirror (FDNLM) are exploited for the laser mode-locking. The FDNLM based on intensity dependent reflection in the laser cavity ensures self-starting and self-sustaining mode-locking while the cascaded chi((2)) lens process contributes to substantial pulse shortening. This hybrid technique enables generation of stable trains of pulses at high-average output power with several picoseconds pulse width. The pulse repetition rate of the laser is 117 MHz with average output power ranging from 0.5 to 3.1 W and pulse duration from 2.9 to 5.2 ps.

Stable Q-switched mode-locked Nd3+:LuVO4 laser by Cr4+:YAG crystal

In use of saturable Cr(4+):YAG crystals, we have demonstrated the stable Q-switched and mode-locked (QML) operation of the Nd:LuVO(4) laser. The operation range of QML in use of the Cr(4+):YAG is larger than that use of SESAM and NLM. The obtained shape of Q-switched envelope, repetition rate and pulse energy are demonstrated to depend on the initial transmittance of the Cr(4+):YAG and reflectivity of the output coupler. Using R = 60% and T(0) = 40%, the highest pulse energy of 77 microJ of each Q-switched envelope, and the highest peak power about 200 kW of Q-switched mode-locked pulses can be obtained at 15 W pump power. It demonstrate the superior characteristic of the Nd:LuVO(4) crystal.

Analysis of a laser-diode end-pumped intracavity frequency-doubled passivelyQ-switched and mode-locked Nd:GdVO4/KTP laser

A diode-pumped intracavity frequency-doubled passively Q-switched and mode-locked c-cut Nd3+:GdVO4/KTP green laser with a Cr4+:YAG saturable absorber is experimentally demonstrated for the first time. Over 95% modulation depth for the mode-locked green pulses has been achieved. By using hyperbolic secant function methods, considering the influences of a continuous pump rate, the upper state lifetime of the active medium, and the excited-state lifetime of the saturable absorber, a rate equation model developed for Q-switched and mode-locked lasers has been given. With this model, the theoretical evaluations are in good agreement with the experimental results, and the width of the mode-locked green pulse was estimated to be about 280 ps.

Direct amplification of picosecond pulses in F2- : LiF crystals

An amplifier of picosecond pulses with an output power up to 1010 W and an energy up to 30 mJ at 1180 nm is developed on the basis of F2- : LiF colour-center crystals. A 3—5-ps, 0.03-mJ probe pulse at 1.18μm was obtained upon intracavity SRS conversion in a passively mode-locked Nd3+ : KGd(WO4)2 laser. The F2- : LiF crystals were pumped by 1053-nm nanosecond pulses from a Nd : YLF laser, amplified in a GLS-22 phosphate glass to an energy of 5 J. The probe SRS pulses were amplified in a four-crystal two-cascade amplifier based on F2- : LiF crystals with the total length of the active medium of 360 mm, by using counterpropagating pump beams. The dependences of the output radiation energy on the pump and input signal energies are measured.

The role of phase-matching and nanocrystal-size effects in three-wave mixing and CARS processes in porous gallium phosphide

Nonlinear-optical interactions, such as second-harmonic and sum-frequency generation and coherent anti-Stokes Raman spectroscopy (CARS), are investigated in porous GaP for the first time by means of a novel laser source based on mode-locked picosecond Nd3+:YVO4 laser and subsequent continuum generation in an optical fiber. The efficiency of the former two nonlinear optical processes is shown to be strongly dependent on the wavelengths of the interacting waves and tends to increase with the decrease of the excitation wavelength. The power of the generated second-harmonic and sum-frequency increases by a factor of 2 and 30, respectively, compared to the crystalline GaP. In contrast, the CARS signal in porous GaP is found to be less efficient than one in crystalline GaP. The observed results are explained in terms of competition of the phase-matching effects in GaP nanocrystals and the enhanced photon lifetime in scattering porous GaP layers.

Mode-locking of neodymium lasers by glasses doped with PbS nanocrystals

Nonlinear optical absorption properties of silicate glasses doped by the PbS nanocrystals were investigated by means of the picosecond pump-probe absorption spectroscopy and absorption bleaching technique. The glass samples were used as saturable absorbers for passive mode-locking of Nd : YAG and Nd : glass lasers. Application of the PbS doped glass together with the active mode-locking and laser cavity quality control enabled the stable of generation of 28 ps and 5 ps duration pulses in Nd : YAG and Nd : glass lasers respectively.

Photoemission monitored cleaning of pure and implanted tungsten photocathodes by picosecond UV laser

New results about picosecond laser cleaning of pure and implanted tungsten photocathodes are reported. During the transport from the preparation cell to the experimentation cell, the exposure of photocathodes to air leads to the contamination and the formation of surface oxides. Before any photocurrent measurement, in situ cleaning of surfaces is required. The surface cleaning effects are investigated in high vacuum (5×10−8 Torr) by using a picosecond mode-locked Nd3+:YAG laser with fifth order harmonic generator (λ=213 nm, τ=16 ps, repetition rate 10 Hz) irradiation. This non-destructive processing allows real-time monitoring by measuring continuously the surface photocurrent. During cleaning, the photocurrent increases versus time and tends to reach a plateau, depending on the pressure in the vacuum cell. The influence of the laser energy density and the effects of surface recontamination by residual gas are investigated. A phenomenological model is developed to describe the laser cleaning. Fitting the experimental data of photoemitted charges with calculated values given by this model is able to estimate the contamination rate and the work function at the surface during the cleaning.

Passive mode-locking of a Nd:YAP laser at 1.3414 μm by using a convex-antiresonant ring unstable resonator

The colliding pulse mode-locking of Nd:YAP lasers which have a plane-convex unstable resonator was investigated at 1.3414 μm. The experimental results showed that the mode-locked output energy reached 57.3 mJ (the biggest pulse in the pulse train was more than 8 mJ), with pulse duration of 78.7 ps. The stability of the dye solution was also investigated.

Widely tunable femtosecond neodymium fiber laser

Continuous tuning of a mode-locked Nd3+ fiber laser over 75 nm is reported. This wide tuning range, which extends over more than twice the FWHM gain bandwidth of Nd:glass, is achieved by optimization of the reflection characteristics and the band-gap energy of the multiple-quantum-well semiconductor saturable absorber. The pulse duration achieved is 300–400 fs over the entire tuning range.

CuInSSe-doped glass saturable absorbers for the passive mode-locking of neodymium lasers

By using a CuInS2xSe2(1−x)-doped glass as an intracavity saturable absorber, passive mode-locking of Nd:YAG and Nd:YAlO3 lasers is obtained. Ultrashort laser pulses are achieved with duration of 16 ps (for Nd:YAlO3 at 1.08 μm) and 36 ps (for Nd:YAG at 1.064 μm), respectively. The intensity dependent transmittance and transient absorption change measurements are performed on CuInS2xSe2(1−x)-doped glasses at 1.08 μm with the use of laser pulses of 15 ps width. The bleaching relaxation time is found to be ∼11 ps.

Very sensitive two-photon absorption GaAs/AlGaAs waveguide detector for an autocorrelator

Two-photon-induced conductivity (TPC) in a reverse biased pin GaAs/AlGaAs optical waveguide is observed, and the intensity-dependence of the photocurrent characterised. When this waveguide was used as the nonlinear detection element of an autocorrelator, an autocorrelation trace of a CW mode-locked Nd3+: YAG laser at 1.06 μm was successfully obtained.

Polarization Properties of a Synchronously Pumped Dye Laser.

A rhodamine 6G (RH-6G) dye laser was actively mode-locked by synchronous pumping using a frequency-doubled mode-locked Nd3+ glass laser. Output light intensities and polarization were measured as a function of the pumping power and dye concentration. Dye laser pulses were observed with a streak camera of 8 ps resolution. The laser pulse width decreased down to the minimum value of 18 ps as the degree of polarization increased up to the maximum value of 0.75. The addition of DODCI as a saturable absorber enhanced the degree of polarization up to 0.9.