Dual Ti:sapphire comb lasers by a fiber laser pumping scheme and a hand-sized optical frequency reference

A dual-comb laser system containing two femtosecond Ti:sapphire (Ti:S) lasers is reported, in which the ultrashort pulses are pumped by one common fiber laser and the influences of the different pumping noise are presented both in time-domain and frequency-domain. In addition, the dimensions of dual Ti:S comb system are reduced due to the implementation of one hand-sized optical frequency reference, from which the needed space and cost for two “self-reference” optics are saved.     

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.     

Stabilizing the frequency of femtosecond Ti:sapphire comb laser by a novel scheme

We demonstrated a novel scheme for scanning the absolute frequencies of a femtosecond Kerr-lens mode-locked Ti:sapphire laser with the repetition rate unaffected, where the carrier-envelop phase of the pulse was controlled by slightly shifting pump beam and the repetition rate was phase locked to a stable radio-frequency oscillator. Since it was the first time to stabilize the frequency of a mode-locked laser by referring directly to the frequency of cesium two-photon-transition (TPT) stabilized diode laser, we evaluated the frequency instability and the frequency accuracy that showed the characteristic of being a comb laser. The feature of the comb laser in this report will be significant for multi-photon spectroscopy where the frequency difference between comb lines plays a key role. PACS  06.30.+v; 42.60.By     

Direct frequency comb generation from an octave-spanning, prismless Ti:sapphire laser

We describe a self-referenced optical frequency comb generator based on an octave-spanning, prismless Ti:sapphire laser. Dispersion compensation is provided by novel double-chirped mirror pairs and BaF2 wedges. Current versions operate at 80 and 150 MHz. The compact prismless design allows system scaling to a gigahertz repetition rate. Its carrier-envelope beat note is intrinsically stable with a signal-to-noise ratio of 30 dB in a 100-kHz bandwidth. The octave is reached at 25 dB below the average power level. The in-loop accumulated phase error is 1.4 rad (20 mHz to 1 MHz). The technique has the advantages of simplicity and stability compared with previous designs.     

Controlling the frequency of the frequency-shifted feedback fiber laser using injection-seeding technique

In this paper we describe the stabilization of the optical frequency comb (OFC) generated by the frequency-shifted feedback (FSF) erbium fiber laser. Frequency of the comb is controlled using the distributed feedback laser diode seeded into the cavity of the FSF laser. When the DFB diode is stabilized to the molecular absorption line of hydrogen cyanide frequency stabilized OFC is obtained.     

Generation of 7-fs laser pulse directly from a compact Ti:sapphire laser with chirped mirrors

A compact femtosecond Ti:sapphire laser resonator consisting of three chirped mirrors and one output coupler was designed. By accurately balancing the intra- cavity dispersions between Ti:sapphire crystal, air and chirped mirrors, we directly generated the laser pulse shorter than 7 fs at the average power of 340 mW with 3.1 W pump. The repetition rate of the laser oscillator is 173 MHz at the centre wavelength of 791 nm, and the ultrabroaden spectrum covers from 600 nm to 1000 nm. To the best of our knowledge, this is the simplest laser resonator capable of generating sub-10 fs laser pulse.     

Frequency comb generation and pulsed operation in a Nd: YLF laser with frequency-shifted feedback

An injection-seeded Nd: YLF laser incorporating frequency shifted feedback generates a frequency comb with a 140 GHz bandwodth and a tunable frequency spacing. Near bandwidth-limited pulses of 31 ps duration have been produced in the seeded laser by matching the frequency shift to a multiple of the cavity roundtrip frequency.     

Multiwavelength picosecond frequency-shifted feedback laser with pulse control by a shaped-gain fiber amplifier

Stable generation of multiwavelength picosecond pulses by a frequency-shifted laser is demonstrated. Pulses are reliably trapped by gain variations provided by a low-extinction transmission filter. Pulses with close parameters are obtained despite considerable difference in amplifier gain at the pulse train wavelengths owing to a strong gain-equalization mechanism provided by the frequency-shifted feedback.     

Characterization of frequency-tripled nanosecond pulsed Ti:sapphire laser injection seeded by a frequency-scanning cw Ti:sapphire laser by use of optogalvanic spectroscopy of silicon atoms

The performance of a narrow-linewidth nanosecond pulsed deep-UV coherent light source consisting of a frequency-tripled nanosecond pulsed Ti:sapphire laser injection seeded by a frequency-scanning cw Ti:sapphire laser has been characterized by using optogalvanic spectroscopy of silicon atoms as a diagnostic. The envelope of the optogalvanic spectrum indicates the pure Doppler broadening of silicon atoms, which was estimated to be as broad as 4 GHz, without the broadening effect from the laser linewidth itself.     

Noncollinear optical parametric amplification in lithium triborate seeded by a cw Ti:sapphire laser

Experimental investigations of a type-I noncollinear phase-matched optical parametric amplification based on lithium triborate, which was pumped by a 5-ns second-harmonic pulses from a Q-switched Nd:YAG, seeded by a cw Ti:sapphire laser at 800 nm, was presented. The experiments generated 2-ns signal output pulses at 800 nm, the maximum signal output pulse energy reached 19 μJ, the corresponding parametric gain was 44 dB. Furthermore, the experiments demonstrate that the 65 nm-FWHM parametric fluorescence gain spectrum could also be observed. A quantitative account of the ultrabroadband parametric fluorescence gain spectrum was given with our theory. The experimental measurements are in agreement with theoretical calculations.     

Analysis of tunable picosecond pulse generation from a distributed feedback Ti：sapphire laser

A distributed feedback Ti:sapphire laser (DFTL) pumped by a 532nm Q-switched pulse is proposed for the generation of tunable picosecond pulses. With coupled rate equation model, the temporal characteristics of DFTL are obtained. The numerical solutions show that the DFTL pulse with a 50-ps pulse duration and as much as 3.SmJ pulse energy can be obtained under 40-m J, 5-ns pulse pumping. The dependence of output pulse width on the laser crystal‘s length, pumping pulse duration, and pumping rate is also discussed in detail.     

Composite frequency comb spanning 0.4-2.4 microm from a phase-controlled femtosecond Ti:sapphire laser and synchronously pumped optical parametric oscillator

A repetition-rate-stabilized frequency comb ranging from the violet to the mid-infrared (0.4-2.4 microm) is obtained by phase locking a femtosecond Ti:sapphire laser and a synchronously pumped optical parametric oscillator to a common supercontinuum reference. The locking results have bandwidths lower than 3 kHz. By changing the locking frequencies, different relative and absolute offsets of the constituent frequency combs are achievable.     

Ti:sapphire laser pumped by a long train of pulses from mode-locked Nd:YAG laser with negative feedback

Investigation of the buildup dynamics of a Ti:sapphire laser pumped by a 500 ns long second harmonic pulse train from a mode-locked Nd:YAG laser with a passive negative feedback using GaAs is reported. The 400 ns long output pulse has a buildup time of 70 ns for a pump energy of 1.25 mJ. A slope efficiency of 15.1% was achieved with a 94% reflective output coupler.     

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。     

钛宝石激光器9.5 fs脉冲输出中的啁啾镜色散补偿

根据钛宝石激光器的要求,实验设计了中心波长800 nm带宽200 nm的啁啾镜,在700—900 nm波长范围内提供约-60 fs²群延迟色散(group delay dispersion,GDD).采用双射频离子束溅射方法进行制备,用实验室搭建的白光干涉仪进行色散性能测试,从测试结果可以看出,制备的啁啾镜的性能和设计值符合得比较好.制备得到的非成对啁啾镜在钛宝石激光谐振腔中进行色散补偿,锁模后分别获得了12 fs和9.5 fs的激光脉冲输出.这是目前报道的使用国产啁啾镜获得的最短的 关键词： 啁啾镜 群延迟色散 色散补偿 钛宝石激光器     

Characterization of an actively linearized ultrabroadband chirped laser with a fiber-laser optical frequency comb

The optical frequency sweep of an actively linearized, ultrabroadband, chirped laser source is characterized through optical heterodyne detection against a fiber-laser frequency comb. Frequency sweeps were measured over approximately 5 THz bandwidths from 1530 nm to 1570 nm. The dominant deviation from linearity resulted from the nonzero dispersion of the fiber delay used as a reference for the sweep linearization. Removing the low-order dispersion effects, the residual sweep nonlinearity was less than 60 kHz rms, corresponding to a constant chirp with less than 15 ppb deviation across the 5 THz sweep.     

Sub-two-cycle pulses from a Kerr-lens mode-locked Ti:sapphire laser

Pulses shorter than two optical cycles with bandwidths in excess of 400 nm have been generated from a Kerr-lens mode-locked Ti:sapphire laser with a repetition rate of 90 MHz and an average power of 200 mW. Low-dispersion prisms and double-chirped mirrors provide broadband controlled dispersion and high reflectivity. These pulse durations are to our knowledge the shortest ever generated directly from a laser oscillator.     

Self-starting 6.5-fs pulses from a Ti:sapphire laser

We demonstrate self-starting 6.5-fs pulses from a Kerr-lens mode-locked Ti:sapphire laser with 200-mW average output power at a pulse repetition rate of ~86 M Hz. This is to our knowledge the shortest pulse ever generated directly from a laser. For dispersion compensation we used a prism pair in combination with double-chirped mirrors, which balances the higher-order dispersion of the prism pair and therefore flattens the average total group-delay dispersion in the laser cavity. For self-starting mode locking we used a broadband semiconductor saturable-absorber mirror.     

Demonstration of microwave frequency shifting by use of a highly chirped mode-locked fiber laser

We report an experimental demonstration of a photonic microwave shifter using a highly chirped mode-locked fiber laser. The system is based on dispersive compression or expansion of highly chirped optical pulses that are amplitude modulated by the microwave signal. Using this technique, we demonstrated frequency shifting of a microwave signal from 10 GHz down to 5 GHz and up to 25 GHz.