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.     

Relative carrier-envelope phase dynamics between passively synchronized Ti:sapphire and Cr:forsterite lasers

We observed and measured the relative carrier-envelope phase difference per round trip between synchronized femtosecond Ti:sapphire and Cr:forsterite mode-locked lasers. The relative carrier-envelope phase slip was directly recorded by heterodyning of the Cr:forsterite laser with the supercontinuum from the Ti:sapphire laser. We also obtained another phase relation by superimposing the third harmonic of the Cr:forsterite laser with the second harmonic of the Ti:sapphire laser. In the latter case we obtained a stable beat signal with a signal-to-noise ratio larger than 30 dB and found a dependence of the beat frequency on the cavity length.     

Broadband phase-coherent optical frequency synthesis with actively linked Ti:sapphire and Cr:forsterite femtosecond lasers

We link the output spectra of a Ti:sapphire and a Cr:forsterite femtosecond laser phase coherently to form a continuous frequency comb with a wavelength coverage of 0.57-1.45 microm at power levels of 1 nW to 40 microW per frequency mode. To achieve this, the laser repetition rates and the carrier-envelope offset frequencies are phase locked to each other. The coherence time between the individual components of the two combs is 40 micros. The timing jitter between the lasers is 20 fs. The combined frequency comb is self-referenced for access to its overall offset frequency. We report the first demonstration to our knowledge of an extremely broadband and continuous, high-powered and phase-coherent frequency comb from two femtosecond lasers with different gain media.     

Octave-spanning Ti:sapphire laser with a repetition rate >1 ghz for optical frequency measurements and comparisons

We demonstrate a self-referenced, octave-spanning, mode-locked Ti:sapphire laser with a scalable repetition rate (550 MHz - 1.35 GHz). We use the frequency comb output of the laser, without additional broadening in optical fiber, for simultaneous measurements against atomic optical standards at 534, 578, 563, and 657 nm and to stabilize the laser offset frequency.     

Attosecond active synchronization of passively mode-locked lasers by balanced cross correlation

A balanced cross correlator, the optical equivalent of a balanced microwave phase detector, is demonstrated. Its use in synchronizing an octave-spanning Ti:sapphire laser and a 30-fs Cr:forsterite laser yields 300-attosecond timing jitter measured from 10 mHz to 2.3 MHz. The spectral overlap between the two lasers is strong enough to permit direct detection of the difference in carrier-envelope offset frequency between the two lasers.     

Optical frequency measurement across a 104-THz gap with a femtosecond laser frequency comb

The frequency-domain mode comb of a Ti:sapphire femtosecond laser centered at 350 THz is broadened to 150 THz (full width at -30 dBc) by self-phase modulation in a single-mode optical fiber. By phase locking continuous-wave lasers to elements of the comb near 1064 and 778 nm, we measure the 104-THz frequency gap between these two lasers with a relative uncertainty of 2.7 x 10(-11) in 1 s.     

Long-term optical phase locking between femtosecond Ti:sapphire and Cr:forsterite lasers

Long-term optical phase-coherent two-color femtosecond pulses were generated by use of passively timing-synchronized Ti:sapphire and Cr:forsterite lasers. The relative carrier-envelope phase relation was fixed by an active feedback loop. The accumulated phase noise from 10 mHz to 1 MHz of the locked beat note was 0.43 rad, showing tight phase locking. The optical frequency fluctuation between two femtosecond combs was submillihertz, with a 1 s averaged counter measurement over 3400 s, leading to a long-term femtosecond frequency-comb connection.     

Wavelength dependent damage in biological multi-photon confocal microscopy: A micro-spectroscopic comparison between femtosecond Ti:sapphire and Cr:forsterite laser sources

Molecular excitation by the simultaneous absorption of two photons provides intrinsic three-dimensional resolution in laser scanning fluorescence microscopy. Thus induced two-photon absorption and the accompanied multi-photon absorption/ionization not only cause photo-bleaching but also cell damage in the vicinity of the focal point. In this paper, we study the wavelength dependent cell damage induced by high intensity femtosecond near infrared lasers. The study was performed with a Ti:sapphire laser and a Cr:forsterite laser. With a longer output wavelength from a Cr:forsterite laser, multi-photon absorption and auto-fluorescence were found to be significantly suppressed and the destructive plasma formation was found to be greatly reduced. Sustained multi-photon spectra can be observed in most plant specimens with a tightly focused Cr:forsterite laser beam under long term irradiation with more than 100 mW laser average power. In contrast, multi-photon absorption induced destructive plasma formation were frequently observed with a tightly focused Ti:sapphire laser beam within seconds with more than 10 mW laser average power.     

Generation of a broadband continuum by a Ti:sapphire femtosecond oscillator with a 1-GHz repetition rate

A five-element Ti:sapphire femtosecond ring oscillator emitting a broadband continuum that ranges from 560 to 1150 nm at -50 dB below the maximum with a repetition rate of 1 GHz is demonstrated. The key element is a slightly convex cavity mirror that increases the self-amplitude modulation of a short pulse inside the resonator. Flat negative intracavity group-delay dispersion is required only for the core spectral part of the pulse. We believe that the device presented will make optical frequency metrology and future optical atomic clocks simpler and more stable. Within the reported ultrabroad spectrum a distinct strong emission band near 655 nm occurs that can be extracted to a powerful femtosecond pulse source far out of the amplification of Ti:sapphire.     

Efficient noncollinear parametric amplification of weak femtosecond pulses in the visible and near-infrared spectral range

We report measurement of efficient amplification of weak femtosecond supercontinuum seed pulses by use of a noncollinear optical parametric process in BBO crystal pumped with 150-fs pulses from a frequency-doubled regenerative-amplified Ti:sapphire laser at 390nm . The highest amplification factor, 10(8) , was achieved for 3x10(-16)J energy seed pulses at wavelength of 560nm.     

Combination of a continuous-wave optical parametric oscillator and a femtosecond frequency comb for optical frequency metrology

We combined a tunable continuous-wave optical parametric oscillator and a femtosecond Ti:sapphire laser frequency comb to provide a phase-coherent bridge between the visible and the mid-infrared spectral ranges. As a first demonstration of this new technique we performed a direct frequency comparison between an iodine-stabilized Nd:YAG laser at 1064 nm and an infrared methane optical frequency standard at 3.39 microm.     

掺Er光纤飞秒激光器载波包络位相偏移的探测

本文介绍了基于掺Er光纤飞秒激光器光学频率梳中光学部分的研制. 实验上采用重复频率为230 MHz的掺Er光纤飞秒激光器,通过放大、光谱展宽以及单臂f—2f系统,在优化及分析相关参数影响的基础上,获得了~30 dB信噪比f₀的输出,为光纤光学频率梳的建立奠定了基础. 关键词： 掺Er光纤激光器 光学频率计量 光纤光学频率梳 光谱展宽     

采用飞秒光纤激光同步泵浦的自启动锁模钛宝石激光研究

针对常规连续激光泵浦钛宝石激光振荡器不能自启动锁模的缺点,采用倍频飞秒光纤激光同步泵浦,通过调节振荡器腔长与泵浦腔长匹配,实现了飞秒钛宝石激光的自启动锁模。实验中采用3.4 W的倍频掺镱光纤激光同步泵浦钛宝石激光振荡器,获得了平均功率大于130 mW、重复频率75 MHz、光谱宽度大于47 nm、脉冲宽度17 fs的锁模脉冲输出,不仅能够稳定可靠地实现自启动锁模,解决了常规钛宝石激光振荡器锁模启动的困难,而且还具有同步输出1040,800,520 nm三束飞秒激光的特点,为进一步开展飞秒激光相干合成以及光参量放大等研究提供了优势基础。     

Generation of two-color femtosecond pulses by self-synchronizing Ti:sapphire and Cr:forsterite lasers

We report a novel technique for the synchronization of two different femtosecond solid-state lasers by crossing of both laser pulses in a Kerr medium. Stable dual-wavelength femtosecond pulses at central wavelengths of 820 and 1250 nm have been obtained. The tolerance of cavity-length mismatch is ~0.6mum , where the pulse widths of the Ti:sapphire and the Cr:forsterite lasers are 18 and 40 fs, respectively, at average powers of 600 and 110 mW. The typical timing jitter derived from the cross correlation is less than 3 fs.     

飞秒钛宝石光学频率梳的精密锁定

经相位锁定后的飞秒钛宝石光学频率梳已经广泛用于绝对光频的测量，这是光频标领域一个革命性的突破.在自建的90MHz飞秒钛宝石激光器的基础上首先采用光子晶体光纤将其光谱展宽到一个光倍频程，接着利用锁相环技术分别将重复频率和载波包络频移同时高精度地锁定到一台稳定度为6×10^－14的Cs钟上，进而得到了稳定度相同的飞秒光学频率梳.     

Tunable continuous-wave operation of a Cr3+,Li+:Mg2SiO4 laser

Room-temperature tunable cw laser oscillation of Cr3+ ions in forsterite crystals (Mg2SiO4) codoped with chromium and lithium has been demonstrated, for the first time to the authors' knowledge, in pumping a crystal with a Ti:sapphire laser into the first excited level of Cr3+ ions (4A2-4T2 transition). The laser is smoothly tunable in the region of 1095-1170 nm. A slope efficiency as great as 4.4% has been achieved.     

Absolute frequency measurement of an acetylene-stabilized laser at 1542 nm

The absolute frequency of an acetylene-stabilized laser at 1542 nm is measured at its second harmonic (771 nm) by use of a femtosecond optical comb based on a mode-locked Ti:sapphire laser. Frequency stability and reproducibility of the acetylene-stabilized laser are evaluated by the femtosecond comb with a H maser as a frequency reference. The absolute frequency of a laser diode stabilized on the P(16) transition of 13C2H2 is determined to be 194 369 569 383.6(1.3) kHz. The acetylene-stabilized laser serves as an important optical frequency standard for telecommunication applications.     

Monolithic 0–f Scheme-Based Frequency Comb Directly Driven by a High-Power Ti:Sapphire Oscillator

A monolithic O-f scheme-based femtosecond optical frequency comb directly driven by a high-power Ti:sapphire laser oscillator is demonstrated.The spectrum covering from 650 nm to 950 nm is generated from the Ti:sapphire oscillator with a repetition rate of 170 MHz.The average output power up to 630 mW is delivered under the pump power of 4.5 W.A 44-dB signal-to-noise ratio(SNR) of the carrier-envelope phase offset(CEO) beat note is achieved under the resolution of 100 kHz and is long-term stabil...     

A double-pass optical parametric amplifier seeded by a blue-shifted output of a photonic-crystal fiber

A blue-shifted output of a photonic-crystal fiber, providing a frequency upconversion of femtosecond Ti:sapphire laser pulses, is used to seed a double-pass optical parametric oscillator (OPA). The OPA is based on a BBO crystal, pumped by 65-mW 150-fs second-harmonic pulses of a Ti:sapphire laser. Gain factors in excess of 10³ are demonstrated for such an OPA, yielding tunable light pulses within the range of wavelengths from 420 to 650 nm, a peak power up to 250 kW, and a typical pulse width of about 200 fs at a repetition rate of 100 kHz. PACS 42.81.Gs; 42.81.Qb     

直接从钛宝石激光器获得超连续光谱

采用啁啾镜和棱镜对相结合补偿色散的方法在自调Q自锁模钛宝石激光器腔内直接产生了超 过一个倍频程的超连续光谱，光谱范围从460nm到1000nm；这是飞秒激光器输出光谱在短波 波段第一次突破500nm.这将使得脉冲的载波包络偏移频率的测量装置得到大大简化，同时也 提高了光频测量的稳定性. 关键词： 超连续光谱 啁啾镜 自调Q自锁模 钛宝石激光器