Development of a femtosecond micromachining workstation by use of spectral interferometry

A workstation that permits real-time measurement of ablation depth while micromachining with femtosecond laser pulses is demonstrated. This method incorporates the unamplified pulse train that is available in a chirped-pulse amplification system as the probe in an arrangement that uses spectral interferometry to measure the ablation depth while cutting with the amplified pulse in thin metal films.     

Regeneration of photon echoes with amplified photon echoes

Photon-echo-based devices have been proposed for many applications in data storage, image processing, and optical communications. Many of these applications would benefit if the output from the photon-echo process could be used as input in a second photon-echo process. We demonstrate the generation of such secondary echoes, using the amplified output from an initial photon-echo process. The amplification is performed with a Pr:ZBLAN fiber amplifier, which gives a gain of more than 300 at 606 nm when pumped with 320 mW of power at 476 nm.     

Highly sensitive direct characterization of femtosecond pulses by electro-optic spectral shearing interferometry

We report what is to our knowledge the first experimental demonstration of spectral shearing interferometry by use of an electro-optic temporal phase modulator to generate the spectral shear. This approach achieves far better sensitivity than nonlinear optical pulse characterization techniques, including other versions of spectral shearing interferometry. Temporal phase modulation is conceptually simple and is implemented easily with telecommunication components. The technique is versatile, and a wide range of pulse durations can be measured with minimal changes in the setup. We demonstrate the accurate characterization of a 156-MHz train of 1540-nm pulses with durations ranging from 750 fs to more than 30 ps after various amounts of chirping, at average powers below 1 microW.     

Time resolved spectral interferometry for single shot femtosecond characterization

Time resolved spectral interferometry is applied to femtosecond pulse coherent measurement. A new configuration that can be directly applied to single shot detection is presented. The efficiency of this self-referenced real-time passive technique is experimentally demonstrated during the characterization of chirped pulses. Additionally, we quantitatively retrieve the spectral phase shift which is associated to the propagation through a F4 glass parallel plate. Numerical results are also reported showing examples of complex pulse characterization. Finally, limitations of the technique are discussed.     

Optical decoherence times and spectral diffusion in an Er-doped optical fiber measured by two-pulse echoes, stimulated photon echoes, and spectral hole burning

Two-pulse and stimulated photon echoes and spectral hole burning were measured on the transition from the lowest component of the ⁴I_15/2 manifold to the lowest component of ⁴I_13/2 of Er³⁺ in a silicate optical fiber at 1.6 K. The two-pulse echo decays gave decoherence times as long as 230 ns for magnetic fields above 2 T. A large field dependent contribution to the homogeneous line width of >2 MHz was found and interpreted in terms of coupling to magnetic tunneling modes (TLS) in the glass. The stimulated echoes measured at 2 T showed spectral diffusion of 0.8 MHz/decade of time between 0.4 and 500 μs. Spectral diffusion in this high field region is attributed to coupling to elastic TLS modes which have a distribution of flip rates in glasses. Time-resolved spectral hole burning at very low field showed stronger spectral diffusion of 5.7 MHz/decade of time, attributed to coupling to magnetic spin-elastic TLS modes.     

Optimum entangled photon generated by micro-ring resonators for new-generation interferometry use

We first propose a concept of a new interferometric technique, where the ultra-narrow spectral width of light pulse generated by using the micro-ring resonators can be used to perform the ultra-high-resolution interferometer. Firstly, the SHG using micro-ring resonators is analyzed and described, Secondly, the increasing in optical path difference (OPD) depends on the full-width at half-maximum (FWHM) width of the generated pulse is discussed. Finally, the optimum entangled photon visibility can be formed the quantum interferometer where the measurement resolution of 10⁻⁵-10⁻⁷ in term of birefringence is achieved. The use of such systems for quantum interferometer, high-resolution interferometer and surface characterization are described.     

Experimental implementation of Fourier-transform spectral interferometry and its application to the study of spectrometers

Various points of the experimental implementation of Fourier-transform spectral interferometry are described. It is shown that deviations from the simple theoretical principle of this technique are induced by the use of a spectrometer followed by a pixellated detector. Potential sources of error are studied and techniques of corrections are demonstrated. Various applications of this technique to the study of spectrometers are discussed.     

All-reflective self-referenced spectral interferometry for single-shot measurement of few-cycle femtosecond pulses in a broadband spectral range

An all-reflective self-referenced spectral interferometry based on the transient grating(TG)effect is proposed for single-shot measuring of the amplitude and phase of ultrashort pulses in a broadband spectral range.Except for a thin third-order nonlinear medium,which was used to generate the TG signal,no transmitted optics were used in the proposed device,and few-cycle pulses in a broad spectral range from deep UV to mid-IR can be characterized.With a homemade compact and alignment-free device,a 5.0 fs pulse at 800 nm corresponding to about two cycles and a 14.3 fs pulse at 1800 nm corresponding to less than three cycles were successfully characterized.     

Subpicosecond photon echoes by using nanosecond laser pulses

Subpicosecond time resolutions have been obtained in photon echoes when a sample was excited by two nanosecond dye laser pulses with a smooth and broad spectrum. The dye laser was pumped by second harmonics of a Q-switched Nd:YAG laser, and the pulse width was 10 ns. The sample was 3% Nd³⁺-doped silicate glass, and the center frequency of the dye laser was tuned at 5910 Å on resonance with the ⁴I_{$\text{9}\text{2}$} ? ²G_{$\text{7}\text{2}$}, ⁴G_{$\text{5}\text{2}$} transition of Nd³⁺. The homogeneous transverse relaxation time T₂ was measured to be 91 ps at 10 K in agreement with the previous measurements by picosecond pulses.     

Demonstration of partial erasing of picosecond temporal optical data by use of accumulated photon echoes

We demonstrated partial erasing of temporal optical data on a picosecond time scale by use of accumulated photon echoes. In a photon-echo memory the temporal data at time tau are stored as a frequency grating of period 1/tau in the absorption spectrum of a material. Partial erasing of the temporal data is achieved by irradiation of the material with a pulse pair at time separation tau , but the phase of one of the pulses is shifted 180 degrees . This process does not produce a frequency grating, and no echo is emitted. The experiment was performed with a dye-doped polymer film. The 180 degrees phase shift was obtained by use of a half-wave plate.     

Extended transient-grating self-referenced spectral interferometry for sub-100 nJ femtosecond pulse characterization

A geometry of transient-grating self-referenced spectral interferometry(TG-SRSI) is proposed for weak femtosecond pulse characterization. By using a reflective microscope objective(RMO), we build a compact,robust, and easy to adjust device with a higher sensitivity to pulse energy in comparison to all previous SRSI methods. A 65 n J∕～ 40 fs∕1 k Hz pulse at 800 nm is successfully characterized, which speaks to the capability of our device to characterize a weak pulse. It is expected to extend the TG-SRSI method to the characterization of femtosecond pulses from oscillators in the near future.     

飞秒钛宝石放大激光脉冲的载波包络相位测量与控制

通过对重复频率为1 kHz的放大飞秒激光脉冲的光谱干涉实验,结合傅里叶变换进行了载波包络相位漂移的实验研究.在此基础上利用锁相环反馈控制技术实现了对载波包络相位的精密锁定,锁定后的激光脉冲稳态相位均方根误差小于80mrad,锁定时间超过3h.同时在理论上分析了光谱干涉测量放大激光脉冲载波包络相位的原理,给出了光谱干涉信号与载波包络相位的关系. 关键词： 飞秒钛宝石放大器 载波包络相位 光谱干涉 超连续     

Single-shot chirped-pulse spectral interferometry used to measure the femtosecond ionization dynamics of air

A novel interferometry technique is presented by which, in one shot, one can measure phase changes with a resolution of tens of femtoseconds while extending the measurement over picoseconds or even longer. The method is based on spectral (frequency-domain) interferometry with a pair of linearly chirped pules as probes. With this technique we obtained single-shot measurements of the rapid phase changes induced by optical field ionization of air. This allowed us to calculate the time profile of the electron density created by an intense short laser pulse.     

Measurement of geometric phase for mixed states using single photon interferometry

Geometric phase may enable inherently fault-tolerant quantum computation. However, due to potential decoherence effects, it is important to understand how such phases arise for mixed input states. We report the first experiment to measure mixed-state geometric phases in optics, using a Mach-Zehnder interferometer, and polarization mixed states that are produced in two different ways: decohering pure states with birefringent elements; and producing a nonmaximally entangled state of two photons and tracing over one of them, a form of remote state preparation.     

Demonstration of highly efficient photon echoes

Highly efficient two-pulse and stimulated photon echoes are experimentally demonstrated in an absorbing medium. Recall efficiencies of 235% and 150% with excellent signal contrast are measured for two-pulse and stimulated photon echoes, respectively, in a Tm:YAG crystal with an absorption length of 3.8. The reported efficiencies do not include any correction for decay or beam profile. We believe that this is the first demonstration of an uncorrected echo efficiency greater than 100% with good signal fidelity in an optically thick medium.     

Dephasing processes as studied by two pulse photon echoes and photochemically accumulated echoes: The question of spectral diffusion in a doped organic polymer matrix

Two pulse photon echoes (2PPE) and photochemically accumulated stimulated photon echoes (PASPE) were measured under identical conditions for the system octaethylporphin in a polystyrene matrix. Experiments at 1.9 K show that both echoes have a different decay behavior. Whereas the 2PPE-signal decays with a time constant of 1300 ps, the PASPE-signal decays faster with a time constant of 600 ps. The different temporal behavior of both signals is tentatively attributed to spectral diffusion.