Intracavity shaping of mode-locked laser pulses

A laser synthesizer of optical pulses is proposed. It is based on injection locking of numerous weakly coupled laser oscillators with a common resonator. A proper shaping of the susceptibility through shaping the pump beam reduces the dispersion of all orders due to the resonance transition and leads to generation of pulses close to the inverse bandwidth of the gain medium. A simple intracavity shaping mechanism allows synthesis of higher-order time supermodes directly from the laser. This technique could be applied to both active and passive mode-locked lasers with homogeneously and inhomogeneously broadened transitions. The possibility of using a compound gain medium is also discussed     

Spectrum and width of mode-locked laser pulses

An analytical theory is given of the spectrum of the pulses generated by a ring laser that is mode locked by a synchronously modulated absorber. A steady-state solution is defined by requiring that, in a round trip, the joint effect of the active medium and the modulated absorber leave the pulses unchanged. The resulting integral equation is solved approximately, and the frequency spectrum of the pulses is obtained in closed form. Although the spectrum cannot be transformed analytically to obtain the pulse shape, the second moment of the shape, which gives a measure of the width, is found. The spectrum and width are found to depend on the curvature of the modulator waveform, near its maximum transmission, and on the gain and bandwidth of the active medium, which is assumed to have a Lorentzian line shape.     

Temporal compression of mode-locked pulses for laser-fusion diagnostics

Regenerative compression of mode-locked laser pulses has been developed to provide a temporally short probe pulse for diagnosing laser-fusion plasmas. A single mode-locked pulse injected into a regenerative amplifier is compressed by an intracavity saturable dye. Analysis indicates the best operational mode and choice of experimental parameters. Experiments using Nd:YAG and Eastman A9740 dye demonstrate an eightfold compression from 120 to 15 ps with a shot-to-shot stability of ±4 percent. An oscillator/regenerative compressor system demonstrates a 15 ps probe pulse synchronized within ±5 ps to a 1000 ps target-heating pulse.     

从锁模脉冲序列中先后选出两个单脉冲的同步研究

采用再生放大腔内的短程放大,利用硅光导开关的长的复合时间,实现光导后产生快上升和下降时间、宽度可调的千伏电脉冲,完成从锁模脉冲序列中先后选出两个单脉冲,这两个单脉冲同步精度高、运转稳定。     

Stabilisation of mode-locked pulses using travelling-wave semiconductor laser amplifier

Numerical and experimental results show, for the first time, that a saturated travelling-wave laser amplifier (TWLA) can be used to amplify and limit the amplitudes of pulses from an actively mode-locked semiconductor laser while removing unwanted secondary pulses.<>     

Demonstration of down-chirped and chirp-free pulses fromhigh-repetition-rate passively mode-locked lasers

Knowledge and control of the chirp parameters of semiconductor lasers is a prerequisite to obtaining transform-limited pulses and/or to compensate for group velocity dispersion in fiber. Here, we report measurements of the sign and magnitude of chirp in high-repetition-rate mode-locked semiconductor lasers. The chirp of these monolithic lasers is measured in the frequency domain, using filtering and cross-correlation techniques. For different injection currents, a range of different chirp values is measured, including strongly down-chirped pulses at higher injection currents and transform-limited pulses to slightly up-chirped pulses at lower injection currents. The pulse chirp and the resulting broadening are due to the algebraic addition of opposite-signed chirps due to saturation of the absorption section and the gain section. These may cancel each other under some conditions, leading to a soliton-like transform-limited pulse     

Stability of passively mode-locked pulses in the fast absorber limit

We have reexamined the stability criterion derived by Haus in the analysis of a laser system which is passively mode locked by a fast saturable absorber. In his stability analysis, Haus required perturbationsdeltaupsilon(t)of the formdeltaupsilon(t) = (sech (t/tau_{p}))^{nu}where τpis the steady-state pulsewidth and ν is a parameter which is varied, to be stable and arrived at an approximate stability criterion. Upon numerical evaluation, Haus observed that the result was very close to the locus of apices separating the two branches of solutions, and proposed it as a stability criterion. Here we test the stability of arbitrary small perturbations and show that the result proposed by Haus is exact.     

Picosecond synchronisation on mode-locked laser pulses by double constant-fraction triggering

A novel technique is introduced for the synchronisation with better-than-30 ps jitter of electrical pulses to ultrafast light pulses at high repetition rate (74 MHz and more). The technique makes it possible to perform time-correlated single-photon counting measurements at picosecond resolution using mode-locked lasers without cavity dumping.<>     

Compression of Q-switched and mode-locked CW Nd:YAG laser pulses

Using the optical compression technique with a single-mode optical fiber and a grating pair, the 85 ps pulses from aQ-switched, mode-locked CW Nd:YAG laser have been compressed by a factor of 30. On average, an overall enhancement of 7 × in the peak power was achieved.     

Amplification of mode-locked semiconductor diode laser pulses in erbium-doped fibre amplifier

Amplification of picosecond pulses from an actively mode-locked semiconductor diode laser in an erbium-doped fibre amplifier pumped at 532 nm is demonstrated. Peak emission was centred on 1.536 mu m and a saturated amplifier gain of 13 dB yielded less than 10 ps pulses with a peak power of 0.58 W at 600 MHz. Optimisation of the mode-locked oscillator allowed amplified peak pulse powers greater than 3 W to be generated.<>     

Cross-correlation studies of pulses from the double mode-locked CW dye laser

A detailed investigation of the dual-wavelength pulse trains from the double mode-locked CW dye laser is made using cross-correlation measurements. Direct displays of pulse shapes and of the system jitter distribution are experimentally determined on a picosecond time scale. Techniques for determining the relative time of generation between the two double mode-locked pulse trains are also demonstrated. A variety of operating modes for this system is discussed in detail, providing further insight into the fundamental mechanisms involved in the production of the two pulse trains.     

The role of cavity dispersion in CW mode-locked dye lasers

The contribution to dispersion of a few components of a mode-locked dye laser cavity has been evaluated. The chirp produced by the self-phase modulation within the saturable absorber has also been evaluated and compared with that resulting from the dispersive components. Cavity mirrors and blocks of transparent materials (glass or quartz) of a length exceeding 1 mm give the largest dispersion. The effect of self-phase modulation, at least for high saturation of the absorber, seems to play a comparable role. The dispersive contributions should influence the mode-locking behavior for pulses of about 100 fs or shorter.     

Coherence analysis of noise-like pulses generated by an erbium-doped fiber mode-locked laser

The noise-like pulses (NLPs) with tunable fraction of the pedestal height in the whole intensity autocorrelation (AC) trace are numerically demonstrated in the designed erbium-doped fiber (EDF) mode-locked laser, which contains the saturable absorber (SA) with nonlinear polarization rotation (NPR), sinusoidal-shaped or Gaussian-shaped filter, two segments of EDFs, and two pieces of single-mode fibers (SMFs) with normal dispersion and anomalous dispersion, respectively. The pedestal ratio of the intensity AC trace can be tuned by changing the gain saturation energies of EDFs. The results show that when the net cavity dispersion is 1.06 ps2, the tuning range of the pedestal ratio for the NLPs can reach its maximum values, which are 0.51—0.89 and 0.58—0.88 for the sinusoidal-shaped and Gaussian-shaped filters, respectively. In addition, an appropriate choice of filter bandwidth is also conducive to obtain a wide range of the tuning pedestal ratio for the intensity AC trace.     

Real-time oscilloscope observation of an ultrafast photodiode response to mode-locked laser pulses

Pulses of 100 ps full width at half maximum (FWHM) have been displayed on a direct current to 5-GHz real-time oscilloscope. The 100-ps duration includes contributions from the oscilloscope, the photodetector, and the laser pulse,Maximum current in the linear regime of the photodiode is ≈3 amperes so that electric pulses of ≈70 ps FWHM and ≈150 volts can be obtained with the laser-detector combination. Results of a simple optical method for determining the exposure time of high-speed electronic cameras are also briefly given.     

Pulse repetition frequency multiplication via intracavity opticalfiltering in AM mode-locked fiber ring lasers

We demonstrate pulse repetition frequency multiplication in AM mode-locked fiber ring lasers using optical filtering realized via an intracavity fiber Fabry-Perot filter (FFP) and show that the generated optical pulses are highly stable in amplitude noise and timing jitter. A 3.477-GHz optical pulse train is generated using a modulation signal of 869.284 MHz, a fourth subharmonic multiple of the 3.48-GHz free spectral range of FFP. The generated optical pulses exhibit a high degree of pulse stability in terms of a large suppression of supermode noise, a low amplitude noise of 0.93 %, and a timing jitter of 1.2 ps     

Picosecond pulses, TEM00mode, mode-locked ruby laser

Picosecond pulses with a single transverse-mode operation have been obtained in a mode-locked ruby laser by using a special rooftop prism cavity. Addition of rhodamine 6G to the dye (DDI in methanol) enabled us to obtain consistently pulses as short as 5 ps.     

Generation of wavelength-tunable transform-limited pulses from amonolithic passively mode-locked distributed Bragg reflectorsemiconductor laser

Generation of wavelength tunable transform-limited picosecond pulses from a monolithic passively mode-locked distributed Bragg reflector (DBR) laser is demonstrated for the first time. A wide tuning range of 12 nm is realized by changing the refractive index of the passive DBR region through a thin-film heater embedded on the DBR section without causing significant changes in pulse characteristics     

All-normal dispersion fiber lasers mode-locked with a nonlinear amplifying loop mirror

We review our recent progress on the design, modeling and construction of all-normal dispersion Yb-doped fiber lasers mode-locked using a nonlinear amplifying loop mirror. The all-fiber nature of the devices we consider permits accurate numerical simulations with minimal approximations or free-running parameters, and we describe in detail a refined numerical modeling scheme that combines generalized nonlinear envelope equations with analytically simulated gain dynamics. Guided by insights obtained from numerical modeling, we have experimentally realized robust, environmentally stable laser designs that offer flexible operation performance for a wide variety of applications. In particular, the unique all-PM-fiber design makes our devices ideally suitable for industrial laser micromachining applications.     

Soliton-supported femtosecond pulses at normal dispersion inoptical fibers

A numerical and analytical examination is made of the subpicosecond properties of a novel type of optical pulse which, with the aid of a supporting soliton pair, may propagate stably at normal dispersion in silica core fibers     

Effect of chromatic dispersion on pulses of arbitrary coherence

Chromatic signal distortion in fibre waveguides depends on the coherence of the optical carrier. The theory derived here covers carriers of arbitrary coherence and arbitrary dispersion characteristics. It gives simple estimates for the available signal bandwidth.