Broadband semiconductor saturable-absorber mirror for a self-starting mode-locked Cr:forsterite laser

We report a low-loss broadband semiconductor saturable-absorber mirror (SESAM) that uses gold film as the reflector. A semiconductor- SiO(2) double-layer stack enhances the reflectivity of the gold film. This low-loss SESAM was used in a mode-locked Cr:forsterite laser to produce self-starting 20-fs-scale laser pulses at 1.3 microm . The structure can be applied to SESAM's for other wavelengths.     

High-peak-power femtosecond Cr:forsterite laser system

Received: 25 June 1998     

Self-starting mode-locked femtosecond forsterite laser with a semiconductor saturable-absorber mirror

We report on a self-starting mode-locked femtosecond Cr:forsterite laser pumped by a diode-pumped Nd:YVO(4) laser. The mode locking is initiated by a semiconductor saturable-absorber mirror (SESAM). We also present the measured group delay of the forsterite crystal and the SESAM.     

Cr:forsterite laser pumped by broad-area laser diodes

We report the demonstration of a Cr:forsterite laser pumped by broad-area laser diodes producing non-diffraction-limited beams. The use of a thin crystal to reduce losses at the lasing wavelength and of short-wavelength pump diodes reduces the lasing threshold to <500mW .Relatively low output powers (5mW) are obtained, but prospects for increasing the power and achieving mode-locked operation of this laser are good and are discussed.     

Dispersion-tuned multiwavelength actively mode-locked fiber laser using a hybrid gain medium

We demonstrate a multiwavelength 10 GHz pulse source using a dispersion-tuned actively mode-locked fiber ring laser incorporated with a semiconductor optical amplifier and an erbium-doped fiber amplifier. Simultaneous seven-wavelength operation of the laser is obtained. The side-mode suppression of all wavelengths is above 30 dB. Smooth wavelength tuning is achieved over more than 12 nm by changing the modulation frequency or the length of the optical delay line. Pulse characteristics are almost constant over the entire tuning span. Wavelength spacing can also be varied from 0.9 to 10 nm by adjusting the dispersion of the cavity. These experimental observations agree well with theoretical analyses.     

宽谱可调谐的全固化Cr:LiSAF激光器

报道了调谐范围达130 nm的的V型腔端面泵浦全固化Cr:LiSAF激光器。研究了V型腔结构的重要参数,优化了腔型设计以提高激光器的效率。激光器自由运转输出时,斜效率最高达39.2%,泵浦阈值最低为32.8 mW。对比分析了双折射滤光片(BF)和棱镜的调谐效果。在腔内插入BF调谐,实现了783~913 nm连续可调谐输出,在840 nm处获得115 mW的最大输出功率,在800~900 nm的区间内,输出功率超过80 mW。用棱镜作为调谐元件,调谐范围达802~887 nm,最大输出功率为6.5 mW。从调谐范围和输出功率看,BF的调谐效果更好。     

Absolute-frequency measurements with a stabilized near-infrared optical frequency comb from a Cr:forsterite laser

A frequency comb is generated with a chromium-doped forsterite femtosecond laser, spectrally broadened in a dispersion-shifted highly nonlinear fiber, and stabilized. The resultant evenly spaced comb of frequencies ranges from 1.1 to beyond 1.8 microm. The frequency comb was referenced simultaneously to the National Institute of Standards and Technology's optical frequency standard based on neutral calcium and to a hydrogen maser that is calibrated by a cesium atomic fountain clock. With this comb we measured two frequency references in the telecommunications band: one half of the frequency of the d/f crossover transition in 87Rb at 780 nm, and the methane v2 + 2v3 R(8) line at 1315 nm.     

Stabilized frequency comb with a self-referenced femtosecond Cr:forsterite laser

A frequency comb is generated with a Cr:forsterite femtosecond laser, spectrally broadened through a highly nonlinear optical fiber to span from 1.0 to 2.2 ,m, and stabilized using the f-to-2f self-referencing technique. The repetition rate and the carrier-envelope offset frequency are stabilized to a hydrogen maser, calibrated by a cesium atomic fountain clock. Simultaneous frequency measurement of a 657-nm cw laser by use of the stabilized frequency combs from this Cr:forsterite system and a Ti:sapphire laser agree at the 10(-13) level. The frequency noise of the comb components is observed at 1064, 1314, and 1550 nm by comparing the measured beat frequencies between cw lasers and the supercontinuum frequency combs.     

Pulse timing stabilization of a mode-locked Cr:LiSAF laser

The pulse repetition frequency of a mode-locked Cr:LiSAF laser has been stabilized to an electrical reference oscillator by use of an electrical feedback technique. The phase and frequency differences between the laser and the reference are detected by use of a digital phase detector, which overcomes the difficulties of a conventional double-balanced mixer. We obtained rms timing jitters of 20 fs (25 mHz-10 kHz) and 7 fs (25 mHz-1 kHz) relative to the reference.     

Femtosecond Cr:forsterite laser diode pumped by a double-clad fiber

We present a compact, all-solid-state femtosecond Cr:forsterite laser. The laser is pumped by diodes through a double-clad fiber. Kerr-lens mode locking is initiated and stabilized by a semiconductor saturable-absorber mirror with a single InGaAs quantum well. This system generates transform-limited 80-fs pulses near 1.3microm . An average power of 68 mW with fluctuation of much less than 1% is obtained with 3.8 W of absorbed pump power. The stability, efficiency, compactness, and potential for scaling to higher power of this system make it an attractive short-pulse source for applications.     

Multipulse operation regime in a self-mode-locked Cr:forsterite femtosecond laser

We report the observation of pulse splitting generated from a self-mode-locked Cr⁴⁺:forsterite laser operating near zero group-velocity dispersion. This new behavior of a femtosecond Cr⁴⁺:forsterite laser could be due to a combination of self-phase modulation, group-velocity dispersion and higher-order phase dispersion inside the laser cavity. The experimental study shows that large third- and fourth-order dispersion inside the cavity leads to the splitting of the solitary pulse into two or three identical pulses, and the results fit reasonably well with those of theoretical calculations.     

Blue-lines pumped Kerr-lens mode-locked Cr:LiSGaF laser

We report a blue-lines pumped femtosecond Kerr-lens mode-locked Cr:LiSGaF laser based on a tight-focusing geometry. With a combination of 488, 476 and 458 nm lines as a pump source, 58 fs pulses centered at 845 nm were generated. The average output power is 30 mW, and time–band product is 0.331, assuming a sec h² pulse shape. Neither acousto-modulator nor physical aperture or slit were used in this cavity.     

Spectral broadening of radiation from a femtosecond Cr:forsterite laser in highly nonlinear fibers

Spectral broadening of radiation emitted by a femtosecond Cr:forsterite laser in highly nonlinear fibers (HNLFs) has been investigated. Tapered HNLFs as well as fibers with constant dispersion and dispersion varying over the fiber length are investigated. The nonreciprocal effect of spectral broadening in fibers with varying dispersion is observed. A supercontinuum is obtained in the range from 990 to 2100 nm.     

Generation of 12-fs pulses from a diode-pumped Kerr-lens mode-locked Cr:LiSAF laser

We demonstrate 12-fs-pulse generation from a diode-pumped Kerr-lens mode-locked Cr:LiSAF laser. This is to our knowledge the shortest pulse ever produced from a mode-locked Cr:LiSAF laser. Based on an improved estimation of the intracavity dispersions, we utilized BK7 glass for the Brewster-prism-pair material.     

Multimodal nonlinear spectral microscopy based on a femtosecond Cr:forsterite laser

We demonstrate a novel multimodal nonlinear spectral microscopy based on a femtosecond Cr:forsterite laser at 1230 nm. By acquiring the whole nonlinear spectrum in the visible and near-NIR region, this novel technique allows a combination of different imaging modalities, including second-harmonic generation, third-harmonic generation, and multiple-photon fluorescence. Combined with the selected excitation wavelength, which is located in the IR transparency window, this microscopic technique can provide high penetration depth with reduced damage and is ideal for studying living cells.     

Stable mode-locking operation in a Cr:forsterite laser with a five-mirror cavity

The experimental finding of more-stable mode-locking operation in a five-mirror cavity than in a conventional four-mirror cavity for a Cr:forsterite laser [IEEE J. Quantum Electron. 33, 1975 (1997)] was interpreted by ABCD-matrix formalism. Since the optimum cavity configuration operation for mode-locking operation was attainable in the middle of the stable cavity condition, we conclude that one can easily achieve KLM alignment and stable mode locking with a five-mirror cavity.     

Mode-locked self-starting Cr:forsterite laser using a single-walled carbon nanotube saturable absorber

We report what we believe to be the first passive mode-locking of Cr:forsterite laser using a single-walled carbon nanotube saturable absorber (SWCNT-SA). The dispersion-compensated Cr:forsterite laser in a self-starting configuration produces nearly Fourier transform-limited pulses as short as 120 fs near 1.25 microm. The maximum average output power of 202 mW obtained with a 5% output coupler at a repetition rate of 79.1 MHz represents, to the best of our knowledge, the highest power level ever reported for SWCNT-SA mode locking of solid-state lasers.     

Wavelength and duration tunable soliton generation from a regeneratively mode-locked fiber laser

A 10-GHz soliton source with pulse duration between 4-8 ps and wavelength continuously tunable from 1530 to 1563 nm is presented. Using regeneratively mode-locking technology, the harmonically modelocked fiber ring laser could work without pulse dropout at room temperature when no cavity length or polarization maintaining mechanism is available. Applying only one 980-nm laser diode pump, the average output power reaches more than 4 mW.     

Efficient laser operation of heavily doped Cr4+:forsterite

Pulsed laser operation of a new high Cr4+ concentration forsterite crystal is reported. Slope efficiencies of 13% and 5% have been obtained for 1064 and 532nm pumping. Results are compared with the performance of three other forsterite crystals. A threefold enhancement in operating efficiency is obtained over standard low dopant-level material. Tuning ranges have also been investigated. This revised version was published online in November 2006 with corrections to the Cover Date.     

Kerr-lens mode-locked polycrystalline Cr:ZnS femtosecond laser pumped by a monolithic Er:YAG laser

We demonstrated a Kerr-lens mode-locked polycrystalline Cr:ZnS laser pumped by a narrow-linewidth linearpolarised monolithic Er:YAG nonplanar ring oscillator operated at 1645 nm. With a 5-mm-thick sapphire plate for intracavity dispersion compensation, a compact and stable Kerr-lens mode-locking operation was realised. The oscillator delivered 125-fs pulses at 2347 nm with an average power of 80 m W. Owing to the special polycrystalline structure of the Cr:ZnS crystal, the second to fourth harmonic generation was observed by random quasi-phase-matching.