Generation of pulsed squeezed light in a mode-locked optical parametric oscillator

The generation of pulsed squeezed light using an optical parametric oscillator (OPO) is discussed. This mode-locked optical parametric oscillator consists of a nonlinear crystal in a cavity which is resonant for both signal and idler waves and which is synchronously pumped by the second-harmonic of an acousto-optically mode-locked cw Nd: YAG laser. The fundamental wavelength of the pump laser provides local oscillator pulses for balanced homodyne detection of squeezed vacuum pulses emitted by the oscillator when operated below oscillation threshold. Photocurrent noise reduction to 30% below the classical shot-noise limit is observed, corresponding to squeezing of the field to a level approximately a factor of two below the mean square vacuum noise.     

Generation of 15 W femtosecond laser pulse from a Kerr-lens mode-locked Yb:YAG thin-disk oscillator

We demonstrated a robust power-scalable Kerr-lens mode-locked(KLM) operation based on a Yb:YAG thin-disk oscillator.15-W,272-fs pulses were realized at a repetition rate of 86.7 MHz with an additional Kerr medium and a 2.5 mm hard aperture in the cavity.247-fs pulses with an average power of 11 W could also be obtained by using a 2.4 mm hard aperture.Based on this shorter pulse,high efficient second-harmonic generation(SHG) was performed with a 1.7-mm-long Li B3O5(LBO) crystal.The SHG laser power was up to 5 W with the power fluctuation RMS of 1% measured over one hour.     

High-power picosecond optical parametric oscillator based on periodically poled lithium niobate

A high-power picosecond optical parametric oscillator (OPO) based on a 47-mm periodically poled lithium niobate crystal is described. More than 12 W of total average power-almost 8 W of signal power at 1.85 microm and more than 4 W of idler radiation at 2.5 microm -is simultaneously extracted from less than 18 W of average pump power. The OPO is synchronously pumped by 80-ps (FWHM) cw mode-locked pulses at 1.064 microm , and its output is tunable from 1.7 to 2.84microm . Nearly transform-limited signal pulses are obtained following the introduction of two intracavity etalons.     

Stable operation of a cw optical parametric oscillator near the signal-idler degeneracy

The frequency stability of a cw optical parametric oscillator (cw OPO) near the signal-idler degeneracy has been studied. The strong tendency of a near-degenerate OPO to mode hop has been suppressed by using a bulk Bragg grating as a spectral filter in the OPO cavity. An experimental demonstration of stable parametric oscillation in a single longitudinal mode of the OPO cavity is reported, together with the capability of tuning the signal-idler difference frequency from 1 to 4 THz. The OPO has potential use in cw terahertz generation.     

Diode-pumped femtosecond Yb:KGd(WO(4))(2) laser with 1.1-W average power

We demonstrate what is to our knowledge the first mode-locked Yb:KGd(WO(4))(2) laser. Using a semiconductor saturable-absorber mirror for passive mode locking, we obtain pulses of 176-fs duration with an average power of 1.1 W and a peak power of 64 kW at a center wavelength of 1037 nm. We achieve pulses as short as 112 fs at a lower output power. The laser is based on a standard delta cavity and pumped by two high-brightness laser diodes, making the whole system very simple and compact. Tuning the laser by means of a knife-edge results in mode-locked pulses within a wavelength range from 1032 to 1054 nm. In cw operation, we achieve output powers as high as 1.3 W.     

All-solid-state cw mode-locked picosecond KTiOAsO4 (KTA) optical parametric oscillator

4 (KTA) optical parametric oscillator (OPO) synchronously pumped by a cw diode-pumped mode-locked Nd:YVO₄ oscillator–amplifier system. The laser system (pumped by 84 W of cw 808-nm diode radiation) generates 7-ps-long pulses at 1.064 μm with a repetition rate of 83.4 MHz and an average power of 29 W. The OPO, synchronously pumped by the 1.064-μm laser pulses, consists of a 15-mm-long KTA crystal (cut for type II noncritical phase-matching) in a folded signal resonant linear resonator. The average powers of the 1.54-μm signal radiation and the 3.47-μm idler radiation are 14.6 W and 6.4 W, respectively. The total OPO output of 21 W corresponds to an internal efficiency of 75%. The experimental investigations include measurements of the OPO output power (and its dependence on the pump power, the transmission of the output coupler, and the resonator length) and of the pulse properties (such as pulse duration and spectral width). The measured results are in good agreement with the predictions of a numerical analysis based on a split-step Fourier method. Received: 4 May 1998     

Actively Q-switched mode-locked Yb-doped fiber laser with high mode-locking contrast

Reliable Q-switched and mode-locked operation of Yb-doped fiber lasers is investigated by employing an acousto-optic modulator (AOM) in a linear cavity configuration. The widths and shapes of the Q-switched envelopes mainly depend on the external modulation frequency of the AOM and near symmetric Q-switched pulses can be generated. Within the Q-switched envelopes, harmonic mode-locked pulses with near 100% modulation depth at the 40 MHz repetition rate are experimentally observed.     

2.5-GHz repetition-rate singly resonant optical parametric oscillator synchronously pumped by a mode-locked diode oscillator amplifier system

We report on an optical parametric oscillator (OPO) that is synchronously pumped directly by a diode laser. This laser is an actively mode-locked master-oscillator power-amplifier system that produces 20-ps pulses at 927 nm with a repetition rate of 2.5 GHz and an average power of 0.9 W. The OPO, which is a singly resonant device based on periodically poled lithium niobate, generates 7.8-ps pulses. The OPO threshold is 300 mW of average pump power, and the maximum average idler output power is 78 mW at a wavelength of 2100 nm. By changing the crystal temperature we can wavelength tune the output in the ranges 1530-1737 nm (signal) and 1986-2348 nm (idler). Rapid wavelength tuning of the OPO over 46 nm (signal) and 74 nm (idler) is achieved through tuning the cavity length over 28 microm by use of a piezoelectric transducer.     

Stable Q-switch mode-locking of Nd:YVO<Subscript>4</Subscript> lasers with a semiconductor saturable absorber

This paper reports on a passively mode-locked and Q-switched Nd:YVO₄ laser generating picosecond pulses with an average output power exceeding 7 W. In a first step Q-switch mode-locking was obtained by self Q-switching of a mode-locked oscillator with appropriate cavity design, pump power and output coupling. In a second system the Q-switching was actively controlled and stabilized by modulating the resonator internal losses with an acousto-optic modulator. In the Q-switch mode-locking operation the laser provided 12.8 ps long mode-locked pulses with a repetition rate of 80 MHz. The repetition rate of the Q-switch envelope was 185 kHz. The maximum pulse energy of a single ps pulse was 0.55 μJ which is 5.5 times the pulse energy measured for cw mode locking. The total energy of the pulses within the Q-switch envelope was 42 μJ. PACS  42.55.Xi; 42.60.Fc; 42.60.Gd     

Experimental study of actively mode-locked semiconductor laser with grating external cavity

In this paper,complete mode-locking optical pulses have been obtained froman actively mode-locked GaAs/GaAlAs semiconductor laser with grating external cavity.Theshortest optical pulse is 7.3 ps measured by second harmonic generation(SHG)autocorrelator.The repetition rate is 995.12 MHz and the central wavelength is 798.4 nm.The effect ofmodulation frequency,modulation current,and bias current on the optical pulses width areinvestigated.     

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.     

Multiwavelength Dispersion-Tuned Actively Mode-Locked Erbium-Doped Fibre Ring Laser with Gain Competition Suppression

Multiwavelength dispersion-tuned actively mode-locked erbium-doped fibre ring laser is demonstrated by incorporating a section of highly nonlinear fibre （HNLF） in the laser cavity. The HNLF and the time gate element （modulator） in the fibre laser successfully suppress the gain competition in the erbium-doped fibre, and thus enable multiwavelength operation. Simultaneous generation of 10 GHz pulses up to eight different wavelengths is achieved. Wavelength, spacing and modes number tuning are investigated by changing fibre cavity length, dispersion, and erbium-doped fibre amplifier power, respectively.     

Broadband, rapidly tunable Ti:sapphire-pumped BiB₃O₆ femtosecond optical parametric oscillator

We report a femtosecond optical parametric oscillator (OPO) based on the nonlinear material BiB?O? (BIBO) pumped directly by a Kerr lens mode-locked Ti:sapphire laser. Using a 1.5 mm long BIBO crystal cut at θ=11.4° for collinear type I (e→o+o) phase matching in the xz optical plane, femtosecond signal pulses across 1.4-1.6 μm, and idler pulses across 1.6-1.87 μm spectral range are generated, limited by the reflectivity bandwidth of the OPO mirrors. The high nonlinear gain and large spectral acceptance for type I interaction in the xz plane of BIBO permit rapid and continuous tuning across the entire range by simple fine adjustment of OPO cavity delay or through small changes in the pump wavelength, without varying any other parameters. Additionally, owing to the near-zero group velocity mismatch and dispersion, the OPO supports broad spectrum as wide as 33 nm, which results in self-compressed signal pulses. For 150 fs pump pulses, signal pulses with durations down to 106 fs with a time-bandwidth product of 0.48 are obtained without the need for intracavity dispersion compensation.     

Tunable, high-repetition-rate, femtosecond pulse generation in the ultraviolet

We report efficient generation of tunable femtosecond pulses in the ultraviolet (UV) by intracavity doubling of a visible femtosecond optical parametric oscillator (OPO). The OPO, based on a 400 microm BiB3O6 crystal and pumped at 415 nm in the blue, can provide visible femtosecond signal pulses across 500-710 nm. Using a 500 microm crystal of beta-BaB2O4 internal to the OPO cavity, efficient frequency doubling of the signal pulses into the UV is achieved, providing tunable femtosecond pulses across 250-355 nm with up to 225 mW of average power at 76 MHz. Cross-correlation measurements result in UV pulses with durations down to 132 fs for 180 fs blue pump pulses.     

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.     

8字形腔波长可调谐锁模脉冲光纤激光器

采用非线性光纤环形镜加脉冲锁模技术及可调谐光纤光栅滤波器,对8字形腔被动锁模掺铒光纤激光器进行了波长可调谐输出的实验研究.在EDFA抽运光功率一定的情况下,通过调节偏振控制器和可调谐光纤光栅滤波器,获得了光谱稳定、重复频率1.1 MHz、输出功率起伏小于0.8 dBm、中心波长在1 548~1 570 nm内连续可调的短脉冲输出.该激光器可实现自启动锁模,且长时间稳定工作无需任何调整.     

Synchronously pumped femtosecond optical parametric oscillator of congruent and stoichiometric MgO-doped periodically poled lithium niobate

A synchronously pumped femtosecond optical parametric oscillator based on congruent MgO-doped periodically poled lithium niobate (c-MgO:PPLN) is reported. The system, operating at room temperature, was pumped by a mode-locked Ti:sapphire laser. The wavelengths of the signal and idler waves were tuned from 870 nm to 1.54 μm and 1.58 to 5.67 μm, respectively, by changing the pump wavelength, the grating period or the cavity length. Pumped by 1.1 W of 755 nm laser radiation, the OPO generated 310 mW of 1080 nm radiation. This signal output corresponds to a total conversion efficiency of 50%. Without dispersion compensation the OPO generated phase-modulated signal pulses of 200 fs duration. Besides the OPO of c-MgO:PPLN, an OPO of stoichiometric (s) MgO:PPLN was investigated. Because of the reduced sensitivity to photorefractive damage, both crystals allowed efficient OPO operation at room temperature. Received: 19 August 2002 / Revised version: 11 December 2002 / Published online: 19 March 2003 RID="*" ID="*"Corresponding author. Fax: +49-631/205-3906, E-mail: andres@physik.uni-kl.de     

Pulse picking by phase-coherent additive pulse generation in an external cavity

We have implemented a simple method for generating an "amplified" phase-coherent light pulse in which a pulse train of phase-coherent, equidistant input light pulses from a mode-locked Ti:sapphire laser is coupled into a ring cavity resonator whose length is matched to the mode-locked pulse repetition frequency at 82 MHz. Pulses are thus coherently superimposed and added inside the buildup cavity and form an intense pulse that is switched out from the cavity via a fast acousto-optic modulator. The method thus provides a pulse train at a reduced and controlled repetition frequency and with higher pulse energies than the original mode-locked pulses.     

Femtosecond fiber-feedback optical parametric oscillator

We demonstrate what is to our knowledge the first synchronously pumped high-gain optical parametric oscillator (OPO) with feedback through a single-mode fiber. This device generates 2.3-2.7 W of signal power in 700-900-fs pulses tunable in a wavelength range from 1429 to 1473 nm. The necessary high gain was obtained from a periodically poled LiTaO(3) crystal pumped with as much as 8.2 W of power at 1030 nm from a passively mode-locked Yb:YAG laser with 600-fs pulse duration and a 35-MHz repetition rate. The fiber-feedback OPO setup is compact because most of the resonator feedback path consists of a standard telecom fiber. Because of the high parametric gain, the fiber-feedback OPO is highly insensitive to intracavity losses. For the same reason, the synchronization of the cavity with the pump laser is not critical, so active stabilization of the cavity length is not required.     

A novel actively and passively mode-locked semiconductor optical amplifier fiber ring laser

A novel actively and passively mode-locked semiconductor optical amplifier fiber ring laser was presented, where semiconductor optical amplifier provided cavity gain and introduced nonlinear polarization rotation, whereas, intensity modulator not only acted as modulator but also polarizer. The pulses with duration below 3 ps (FWHM) and peak power about 16 mW at a repetition rate of 10 GHz can be obtained in our system and the system stability may be enhanced. To investigate system parameters effects on mode-locked pulses, a theoretical model was developed.