Low Timing Jitter and Tunable Dual-Wavelength Picosecond Pulse Generation from a Fabry--Pérot Laser Diode with External Injection

A novel scheme to generate tunable dual-wavelength optical pulses with low timing jitter at arbitrary repetition rates is proposed and demonstrated experimentally. The pulses are generated from a gain-switched Fabry-Pérot laser diode with two external cw beams for injection seeding simultaneously. The cw light is generated by two independent distributed feedback laser diodes, and their wavelengths can be tuned independently by two temperature controllers. The dual-wavelength pulses with the pulse width of 57 ps, the timing jitter of 340 fs, are obtained. The sidemode-suppression ratio of the output pulses is better than 23dB over a 10-nm wavelength tuning range.     

A long-pulse xenon ion laser as a pumping source for dye lasers

A simple xenon ion laser that is either sealed or has a gas flow mode is described. The laser delivered long pulses ( 15 μs) of almost 1 kW peak power. It has been used to pump a dye laser employing the same configuration as cw dye lasers. The system is inexpensive and can be mode-locked, enabling it to yield ultrashort pulses comparable in duration to those delivered by cw argon laser-pumped dye lasers but with much higher peak powers.     

光纤零色散波长的精确测量

提出了一种测量单模光纤零色散波长的新方法,即让可调谐的连续波（波长λｓ）和波长λｐ位于光纤正常色散区的泵浦脉冲串在光纤中共同传输,交叉相位调制与群速度色散的相互作用可使得连续波的强度得到调制。对连续波λｓ进行调谐,若连续波被调制成亮脉冲,则表明λｓ位于光纤负色散区;若连续波被调制成暗脉冲,则表明λｓ位于光纤正色散区;若连续波的强度不能被调制,则表明λｓ位于光纤的零色散波长λ０附近。利用这一方法对长度为０．９８ｋｍ的色散位移光纤的零色散波长进行了测量,测量精度可达０．５ｎｍ。     

Recent developments in picosecond photochronoscopy

Recent developments in the techniques of generation and measurement of picosecond and sub-picosecond pulses from mode-locked lasers are reviewed. Particular attention is paid to frequency tunable, bandwidth-limited pulses from dye lasers, especially the cw dye laser. In measurement the main emphasis is put on the rapid advances of the last few years in ultra-fast streak-cameras, ans the recent developments in streak-camera synchronization to a cw mode-locked laser is described. Future prospects for shorter wavelenght pulses in the uv and vuv are briefly considered.     

Production of 300W,nanosecond, transform limited optical pulses

Intense nanosecond pulses have been produced from a cw dye laser using a dye amplifier pumped by 6 ns nitrogen laser pulses. The pulses have a transform limited spectrum and are convenient for coherent propagation experiments.     

Significance of intra-cavity power density in synchronous mode-locking of CW-dye lasers

It is shown that there is a well-defined relation between the intra-cavity power density and the temporal structure of ultrashort light pulses generated by a synchronously pumped cw dye laser. To obtain pulses of good quality with high output power the beam cross-section in the lasing medium must be large, because the best performance is achieved at low power density.     

Diode-pumped, high-average-power femtosecond Cr3+ :LiCAF laser

We demonstrate a high-average-power continuous wave (cw) and cw mode-locked Cr3+ :LiCAF laser pumped by broad-area laser diodes. In cw lasing experiments, up to 580 mW of output was obtained with 4.35 W of incident pump. A semiconductor saturable absorber mirror was used to initiate stable, self-starting, mode locking. In the cw mode-locked regime, the Cr3+ :LiCAF laser produced nearly transform-limited, 67 fs long pulses near 800 nm with an average output power of 300 mW. The pulse repetition rate was 120 MHz, with a pulse energy of 2.5 nJ.     

Photorefraction in LiNbO<Subscript>3</Subscript>:Fe crystals with femtosecond pulses at 532 nm

Photorefractive index gratings are written into iron-doped lithium niobate crystals using femtosecond laser pulses and cw light, both having a wavelength of 532 nm. The saturation value of the refractive index changes in as-grown samples is found to decrease with increasing peak pulse intensity. Furthermore, in oxidized crystals, writing with femtosecond pulses is much faster than with cw light and retains about the same writing speed than in as-grown crystals. We propose a charge transport model that addresses the special case of recording with high intensity femtosecond pulses.     

Self-switching of optical pulses in dispersion-imbalanced nonlinear loop mirrors

We report a novel nonlinear filter that transmits and shortens incident pulses while rejecting cw background as well as resonant continuum. A relative extinction of 22dB is reported for the cw background.     

Frequency-modulation-mode-locked optical parametric oscillator

We demonstrate a novel technique for the generation of mode-locked pulses from a continuous-wave (cw) optical parametric oscillator (OPO). The technique is based on the deployment of a phase modulator in combination with an antiresonant ring interferometer internal to a cw OPO, simultaneously providing spectral broadening and phase-to-amplitude feedback modulation. The scheme is implemented in a doubly-resonant cw OPO based on MgO:sPPLT, configured in a standing-wave cavity and pumped at 532 nm. With the phase modulator activated and the cavity length synchronized, a stable train of 800 ps pulses is generated at a repetition rate of 160 MHz. Using single-pass second harmonic generation (SHG) of the OPO output, we observe a four times enhancement in SHG compared with cw operation, confirming the real achievement of energy concentration as a result of mode-locked operation.     

Highly efficient, low-cost femtosecond Cr3+ :LiCAF laser pumped by single-mode diodes

We describe efficient continuous-wave (cw) and cw mode-locked operations of a Cr3+ :LiCAF laser, pumped by inexpensive single spatial mode laser diodes. Up to 280 mW of cw output power was obtained with 570 mW of absorbed pump power, with a corresponding slope efficiency of 54%. Continuous tuning between 765 and 865 nm was demonstrated using a fused silica prism. A semiconductor saturable absorber mirror was used to initiate and sustain stable, self-starting, mode-locked operation. In cw mode locking, the laser produced 72 fs (FWHM) duration pulses, and 1.4 nJ pulse energy, at an average output power of 178 mW. Electrical to optical conversion efficiencies of 7.8% in mode-locked operation and 12.2% in cw operation were demonstrated.     

Spectral distribution measurement of single laser pulses

We show that the transition from cw laser emission to ultrashort pulses can be a non-equilibrium phase transition of first or of second order depending on laser length.     

Two-level model of a superradiant laser with distributed feedback

Numerical one-dimensional simulation of the superradiance phenomenon in a sample of a two-level medium with cw pumping under the conditions of resonant Bragg backscattering of counterpropagating waves has been performed. A range of parameters is determined in which a superradiant laser generating a chaotic sequence of ultrashort high-power pulses can be implemented, and the properties of these pulses are studied.     

Experimental Study of a Pulsed Ytterbium-Doped Fibre Laser with Fast and Slow Saturable Absorbers in a Linear Cavity

We present a linear-cavity stretched-pulse fibre laser and by semiconductor saturable-absorber mirrors. A with mode locking by a nonlinear polarization rotation Q-switched mode-locking cw train and a mode-locking pulse train are obtained in the experiment. We investigate the effects of the equivalent fast saturable absorber and the slow saturable absorbers in experiment. It is found that neither the nonlinear polarization evolution effect nor a semiconductor saturable absorber mirror is enough to produce the stable cw mode-locking pulses in this experiment. A nonlinear polarization evolution effect controls the cavity loss to literally carve the pulses; semiconductor saturable absorber mirrors provide the self-restarting and maintain the stability of the modelocking operation.     

Picosecond and subpicosecon pulse generation in synchronously pumped mode-locked cw dye lasers

Generation of tunable near-infrared picosecond and subpicosecond pulses in a synchronously pumped cw mode-locked Oxazine-1-perchlorate dye laser has been investigated for different values of the important system parameters. The experimental results confirm the predictions of a simple theoretical model which describes the steady-state pulse duration in terms of gain modulation strength, pump power, intracavity bandwidth, pump pulse length and cavity detuning. For a pump-pulse length of 100 ps and a bandwidth of more than 500 Å for the intracavity tuning element dye-laser pulses as short as 0.35 ps have been obtained. Under these conditions up to 100 mW of average output power were provided. In addition, mode-locking of an Oxazine 750 dye laser by synchronous pumping with the cw train of pulses obtained from the Oxazine-1-Perchlorate laser is reported.     

Mid-infrared pulse generation using a sub-picosecond OPO

We describe a synchronously pumped LBO parametric oscillator pumped by a cw mode-locked Ti:Sapphire laser. We demonstrate the synchronization between the pump pulses and the signal pulses by measuring a 100 fs cross correlation. We then generate pulses tunable from 2.6 to 5.3 µm by mixing the signal and idler pulses in an AgGaS₂ crystal and obtain as much as 400 µW of average power.     

掺铒光纤光栅的开关动力学特征研究

研究在连续光入射下掺饵光纤光栅的开关动力学特征，发展其开关过程有类似于相变的特征。数值结果表明，主动光纤光栅在连续光条件下更适合于脉冲串产生。     

Generation of picosecond optical phase conjugate pulses using cw mode-locked lasers

Low power picosecond optical phase conjugation has been demonstrated using cw mode-locked argon-ion and dye lasers via 4-wave mixing in ruby. Streak camera and power measurements show that the generated pulses are identical to the input pulses.     

UV-excimer-laser ablation of polymethylmethacrylate at 248 nm: Characterization of incubation sites with Fourier transform IR- and UV-Spectroscopy

Ultraviolet and Fourier transform infrared (FTIR) spectroscopic experiments with thin films of polymethylmethacrylate (PMMA) are reported. During the incubation with 248 nm excimer laser light or continuous (cw) UV light sources PMMA exhibits a rapidly increasing, broad UV absorption. This is caused by the production of unsaturated species, which are detected in the infrared spectrum of irradiated PMMA films. The spectral data explain the incubation process preceding the ablation of PMMA at 248 nm. Taking advantage of the increased UV absorption, cw light incubated PMMA films can be selectively ablated by standard 308 nm excimer laser pulses.     

Multiple-beam interference patterns in optical fiber generated with ultrafast pulses and a phase mask

We compare the cladding patterns present in grating structures fabricated with an ultrafast laser and a phase mask with a cw beam interference model. We find that the observed patterns agree well with the model results for picosecond pulses; however, for femtosecond pulses, we show that the full bandwidth and the pulsed nature of the sources must be considered because the pattern can be affected by group-velocity walk-off. An interesting consequence of order walk-off is the possibility of pure two-beam interference generation with a phase mask in the femtosecond pulse regime.