Three-dimensional optical storage in fused silica using modulated femtosecond pulses

Three-dimensional bitwise optical recording with a density of 500 Gb/cm3 in fused silica using a Ti:sapphire femtosecond laser modulated by binary digits is demonstrated. Laser pulses modulation is realized by modulating two circuits of trigger pulses signal which are used to control laser pulses trapping and switching out from cavity, respectively. Bits are optically readout in both a parallel reading (phase-contrast) and a serial reading (confocal-type) methods. The method for modulating laser pulses can also be used in all of pulsed laser systems which operate in cavity-dumping configuration.     

Compression of femtosecond optical pulses with dielectric multilayer interferometers

The group velocity dispersion of a multilayer thin film Gires-Tournois interferometer used for reflection of ultrashort optical pulses can be continuously tuned from positive to negative values at an extremely low loss in pulse energy. Thus, this device can be applied for compression of femtosecond pulses independent of the sign of the frequency chirp by simple angle tuning of the interferometer. This has been demonstrated with up-chirped 210 fs pulses which have been compressed to an almost transform-limited duration of 115 fs.     

Generation of high-power femtosecond pulses near 1.5 μm using acolor-center laser system

The authors have developed a high-power F-center laser system capable of generating femtosecond pulses with energies exceeding 50 pJ at wavelengths near 1.5 μm. Short pulses (140 fs) from an additive-pulse mode-locked NaCl laser are amplified in a multipass NaCl amplifier at kilohertz repetition rates. The system can generate peak powers approaching 500 MW, with wavelengths tunable from 1.52 to 1.64 μm. The amplified pulses are used to generate a continuum in various solid media without optical damage. The continuum generated in BaF₂ is extremely broad, extending from below 400 nm to 3.5 μm. Construction and operating details are discussed as well as the system's utility for femtosecond measurements in the infrared and high-power experiments     

Reflection of femtosecond optical pulses from multiple-layer dielectric mirrors--Analysis

We present an analytical treatment of the reflection of femtosecond pulses from broad-band multiple-layer dielectric mirrors. In particular, closed-form expressions are given for the reflected pulse amplitude which includes the dispersive effect of the cubic phase term. It is shown that this term is still insufficient to accurately describe certain experimental results obtained with 20-fs optical pulses. We introduce an alternative technique which describes the phase branches analytically and yields accurate closed-form expressions for the reflected pulse amplitude in terms of complementary error functions having real or complex arguments.     

Propagation characteristics of femtosecond pulses in erbium-dopedmonomode optical fibers

The spectral and temporal characteristics of femtosecond optical pulses (durations of ~120 fs, wavelength of 1.5 μm) propagating in erbium-doped monomode fibers have been experimentally studied in detail. Distinct spectral broadening and shifting processes have been observed for three types of fibers (two different dopant concentrations and one erbium-free sample for comparison). Whereas only a small amount of spectral broadening occurs in the Er-free fiber, there is a major spectral extension (1.3-1.7 μm) for the low-doped erbium fiber, in which a self-phase-modulation mediated four-wave-mixing process has been observed. Autocorrelation data for the exiting pulses indicate the existence of strong pulse shaping and breakup effects in the Er-doped fibers     

Generation and amplification of ultrashort optical pulses

During the last two years since the 1966 Iternational Quantum Electronics Conference further progress toward obtaining high-power light pulses has taken place. An effective method of ultrashort light pulse generation (mode locking) has been developed, further development of the method of coherent amplification of light pulses has been recorded, and new prospective ideas have been put forward. The present paper briefly reports on the data obtained by us in these directions.     

具有空间高斯分布的飞秒光脉冲在自由空间传播时的畸变

本文利用基尔霍夫-菲涅耳公式,计算了空域和时域均为高斯分布的飞秒光脉冲在自由空间传播时产生的脉冲畸变.当脉冲时间宽度达到甚至小于1个光周期时.这种畸变尤为明显.     

Generation of frequency-chirped optical pulses in a large-slippagefree-electron laser

We have investigated the optical output of the free-electron laser for infrared experiments (FELIX) when it is driven by an electron beam with a ramped energy. We show that the applied slow ramp on the electron beam energy leads to a frequency chirp on each picosecond optical pulse. Typical values for the chirp are 0.2% frequency sweep across a 1.5-ps-long optical pulse. The optical pulses were analyzed with a double-grating pair and with a second-order autocorrelator. The pulse duration was reduced in the double-grating pair by 20%. A linear dependence of the chirp on the cavity desynchronization was measured     

可调谐双波长低抖动增益开关光脉冲的产生

提出了一种产生可调谐双波长低抖动超短光脉冲的新方法。采用外光注入法来降低增益开关F-P激光脉冲的时间抖动,实现了脉冲光谱的双波长可调谐输出。实验中利用两个多量子阱DFB激光器作为外部种子光源,通过温度控制和偏振态调节使外部种子光有效地耦合到增益开关F-P激光器中,输出的光脉冲时间抖动(均方根)从2.57ps降低至1.06ps,双波长的边模抑制比可达25dB。通过改变DFB激光器和F-P激光器的工作温度,可实现波长从1540nm到1560nm的可调谐输出。     

Generation of picosecond optical pulses with highly RF modulated AlGaAs DH laser

AlGaAs DH lasers with strong RF modulation superimposed on the relatively low dc bias below the oscillation threshold were demonstrated to be feasible for generation of a train of approximately 30 ps optical pulses at a repetitive frequency of sub-GHz range. The pulse envelope width was measured by three different methods: a fast response photodetector, the second-harmonic generation (SHG) correlation method, and an ultrafast streak camera. The results of the SHG correlation and the streak camera agreed fairly well. In order to explain the generation mechanism and the characteristics of these ultrashort optical pulses in a highly RF modulated semiconductor diode laser, the rate equation analysis was performed and the results were generally in good agreement with the experiment. Furthermore, from the computer simulation for the analysis of the SHG correlation traces, it was inferred that an individual ultrashort optical pulse has internal substructures made of fluctuating fields whose spike widths were of the order of subpicoseconds, due to the randomness of the phases among lasing modes.     

Linking two optical frequency combs by heterodyne optical phaselocking between diode lasers at 2.6-THz frequency-difference

Two optical frequency combs (OFC) with total span of 8 THz have been realized and linked by injecting two laser beams into one OFC generator. Two lasers whose frequencies were separated by 2.6 THz were heterodyne phase-locked to link the two combs. The phase-locked loop bandwidth was 1 MHz and the phase error variance was estimated to be 0.08 rad²     

Degenerate-cross-phase modulation of femtosecond laser pulses in a birefringent single-mode optical fiber

Degenerate-cross-phase modulation has been observed for femtosecond laser pulses propagating through a short birefringent single-mode optical fiber. The difference in the spectral broadening of the two output polarization components of a single laser pulse was attributed to the combination of self-phase modulation and degenerate-cross-phase modulation processes in the optical fiber. Theoretical simulations based on the solutions of the two coupled nonlinear Schrodinger equations are in good agreement with the measured results.     

Generation of balanced subnanosecond pulses using step-recoverydiodes

A method for generating balanced subnanosecond pulses is described. By using pulsed bias techniques to excite a step-recovery diode via a conventional ferrite balun transformer, a balanced step waveform can be taken directly from the diode itself, eliminating the requirement for a broadband output balun transformer. The resulting pulses are suitable for applications in broadband antenna excitation, time-domain reflectometry and high-speed sampling bridges     

Generation of a frequency sextupled optical millimeter wave with a suppressed central carrier using one single-electrode modulator

We have theoretically and experimentally investigated the generation of optical millimeter wave (mm-wave) generation based on a quadrupling and sextupling technique using one single-electrode intensity modulator (IM) with a simultaneously suppressed optical central carrier. By adjusting the bias voltage and utilizing proper peak-to-peak voltage of the RF signal drive on the IM, undesired sidebands can be suppressed. Based on this rule, an experiment was performed to generate 48 and 72-GHz optical mm-waves using a sinusoidal clock source running at only 12 GHz.     

双色飞秒强激光作用下的CO2分子高次谐波

实验研究了双色场条件下CO2 分子高次谐波辐射, 通过改变充气气压获得偶次谐波最大为28th。此外,通过变化气体盒内激光焦点位置从而显著改变24th 谐波光子能量。实验发现在气体盒內谐波强度存在两个极大值,这是因为不同区域内相位匹配出现长短轨道选择的结果。实验结果表明,双色场驱动的分子高次谐波可成为具有发展前景的多波长可调谐相干XUV 光源。     

基于SPIDER法测量飞秒脉冲的数值计算与模拟

为了测量飞秒脉冲的振幅和相位,采用光谱相位相干电场重构法(SPIDER)的光谱图数值分析公式,对高斯强度分布的线性啁啾脉冲、立方相位啁啾脉冲进行数值计算与数值模拟,并重构出飞秒脉冲的光谱相位,其模拟的结果与理论符合较好,光谱相位相干电场重构法能完全测量飞秒脉冲的振幅和相位.     

光纤通信中高阶色散对飞秒光脉冲传输影响的数值研究

数值模拟了光纤通信中三阶色散和四阶色散对飞秒光脉冲传输的影响,结果表明三阶色散和四阶色散都会影响通信质量,三阶色散起主要作用,正常色散使光脉冲向前沿偏移,反常色散使光脉冲向后沿偏移,它们都使脉冲展宽且形成振荡带;四阶色散使脉冲展宽且光谱出现旁瓣。     

Generation of surface electromagnetic waves in semiconductors under the action of femtosecond laser pulses

It is demonstrated that intense photoexcitation of the surface of a semiconductor with femtosecond laser pulses can induce fundamental changes in its optical response and ensure conditions for the generation of surface electromagnetic waves of various types. The connection between electronic processes initiated in the surface layer by photoexcitation and the formation of periodic surface microstructures observed in experiments on irradiation of Si targets is considered. The importance of photoemission in the processes taking place under ultrashort excitation is confirmed.     

Generation of transform-limited optical pulses using a combinationof a gain-switched diode laser and a semiconductor opticalamplifier

We introduce a novel method for generating nearly transform-limited picosecond optical pulses at multi-gigahertz repetition rates. Frequency-chirped optical pulses are first produced using a gain-switched semiconductor diode laser, and they are subsequently amplified by a semiconductor optical amplifier. The red frequency chirp in the gain-switched pulses is compensated for almost completely as a result of gain-saturation-induced self-phase modulation occurring in the amplification process. Experimentally, we have successfully generated nearly transform-limited 28-ps optical pulses at a 5-GHz repetition rate using a distributed feedback diode laser and a traveling wave semiconductor optical amplifier     

Generation of complex microwave and millimeter-wave pulses using dispersion and Kerr effect in optical fiber systems

We study a new method to synthesize high-frequency complex microwave and millimeter-wave pulses using dispersion, Kerr effect, and group velocity delay in optical fiber systems. The profile of the generated pulses can be controlled by changing the parameters of the optical system. Nonlinear propagation effect in fibers can be used to generate electrical pulses with an extremely broad spread spectrum. Soliton trapping can be used to generate electrical pulses with a controllable frequency. Implicit results are given when dispersion or nonlinear effect can be neglected. Generation of electrical pulses with a controllable microwave frequency is demonstrated experimentally using a Mach-Zehnder interferometer and a chirped fiber Bragg grating.