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Entangled two-photon spectroscopy is expected to provide advantages compared with classical protocols. It is achieved by coherently controlling the spectral properties of energy-entangled photons. We present here an experimental setup that allows the spectral shaping of entangled photons with high resolution. We evaluate its performances by detecting sum frequency generation in a non-linear crystal. The efficiency of the process is compared when performed with classical or entangled light., Comment: 26 pages

A new optical design of tiled single grating pulse compressor has been proposed, set-up and studied. The parametric space, i.e. the laser beam diameters that can be accommodated in the pulse compressor for the given range of compression lengths, has been calculated and shown to have up to two fold enhancement in comparison to our earlier proposed optical designs. The new optical design of the tiled single grating pulse compressor has an additional advantage of self compensation of various tiling errors like longitudinal and lateral piston, tip and groove density mismatch, compared to the earlier designs. Experiments have been carried out for temporal compression of 650 ps positively chirped laser pulses, at central wavelength 1054 nm, down to ~235 fs in the tiled grating pulse compressor set up with the proposed design. Further, far field studies have been performed to show the desired compensation of the tiling errors takes place in the new compressor.

Highly charged ions (HCI) have a few tightly bound electrons and many interesting properties for probing fundamental physics and developing new frequency standards [1,2]. Many optical transitions of HCI are located in the extreme ultraviolet (XUV) and conventional light sources do not allow to study these transistions with highest precision. For this reason, we are developing an XUV frequency comb by transfering the coherence and stability of a near infrared frequency comb to the XUV by means of high-harmonic generation (HHG) [3–4]. Reaching intensity levels necessary for HHG 1013W/cm2), while operating at high repetition rates (100 MHz) for large comb line spacing, is challenging. Therefore, the laser pulses are first amplified in a rod-type fiber to 70 W and compressed to sub-200 fs in a grating and prism compressor. Afterwards, pulses are resonantly overlapped in an astigmatism-compensated femtosecond enhancement cavity, which is locked to the frequency comb. To achieve high stability and low-noise performance, the cavity is built on a rigid titanium structure with vibrational decoupling from the vacuum pumps. High-harmonics will then be generated in a target gas in the tight focus of the cavity and coupled out of the cavity by minus-first order diffraction from a small-period grating etched into a high-reflective cavity mirror [5]. Mirror degradation due to contamination and hydrocarbon aggregation is prevented by operating the whole cavity under ultra-high vacuum conditions. A differential pumping scheme will enable high target gas pressures in the laser focus without impairing the pressure elsewhere in the chamber [6].

We demonstrate an efficient method of mid-IR femtosecond-laser-pulse self-compression in transparent dielectrics based on a suitable selection of the parameters of the medium and laser radiation. We discuss the principle of selection of the nonlinear medium for ultrashort-pulse self-compression. We show that the proposed combination of the Kerr nonlinearity and negative group-velocity dispersion in a set of transparent dielectric crystals (CaF2, BaF2, YAG, etc.) provides a compression of the incident laser pulse to a 1–2 cycle pulse width.

As a consequence of the general experimental challenge to detect signals in mid-IR range, taking dispersive chirped near-IR laser pulses as the injected signal source seems to be an artistic route avoiding the daunting mid-IR stretcher and constantly was applied in moderate energy mid-IR optical parametric chirped-pulse amplifications (OPCPA) systems. In this paper we study the wavelength effect on pulse stretching and compressing in detail. Beginning with the theoretical analysis on each dispersion term of grating pairs, we evaluate the residual dispersions when pulse stretcher and compressor work at distinct wavelengths, which shows that this wavelength effect will result in poorly compressed pulses far from transform-limited. Via proof-of-principle experiments based on mid-IR OPCPAs and corresponding numerical simulations, we show that this artful configuration led to un-compressible pulses of ∼2 ps with a time-bandwidth product of ∼ 10 when the chirped-pulse duration is ∼400 ps. To overcome this effect, we demonstrate a simple design of pulse stretcher and compressor. The presented design consisted of a reflection grism-pair compressor can simultaneously cancel the quadric and cubic dispersions of conventional grating based stretcher, showing a potential ability of supporting high-contrast, sub-100-fs pulse-duration and 10,000× of pulse expansion.

We report on our high-contrast laser based on high-contrast, high-energy seed injection, low-gain optical parametric chirped pulse amplification (OPCPA), and Nd:glass amplifiers, which can be used as the high-contrast front end of a high-power Nd:glass chirped pulse amplification (CPA) laser system. The energy of the stretched 1053 nm high-contrast seed pulse increases to 60 μJ by optimizing the frequency doubling crystal in the pulse cleaning device. After passing through a two-stage low-gain OPCPA, a 2-pass 2-rod Nd:glass amplifier, and a compressor the amplified pulse of 131 mJ/282 fs is achieved. The third-order correlation scanning measurement shows that the pulse contrast in the tens of ps range is about 10−7–10−8. With the high-contrast seed passing through the stretcher and compressor only, the contrast measurement indicates that the stretching-compressing process leads mainly to the contrast degradation of the amplified pulse.

The characteristic of echo from target is one of the most important factors that influence the performance of laser detection system. The Signal-to-Noise Ratio (SNR), retroreflected power and detecting precision were analyzed in time-domain, and ultrashort pulse laser was introduced to improve the performance of laser detection system. Atmospheric turbulence-induced pulse broadening according to propagation distance and turbulence strength was analyzed and calculated. Furthermore, the pulse broadening results of turbulence and incident angle were compared. The improvement of laser detection system based on ultrashort pulse laser was summarized. The results show that the detection performance was determined by laser width which was induced by atmospheric propagation in close quarters and the angle of incidence in terms of vertical detecting. However, compared to the influence of incident angle, pulse width boarding induced by atmospheric was neglectable. The simulated results show that the SNR and resolution of laser detection system can be improved efficiently by ultrashort pulse laser.

Fourier-transform-limit pulses are required by recent petawatt-class femtosecond chirped-pulse amplification lasers for increasing peak powers, but which are challenged by the residuals of the high orders of dispersion, for example the fourth-order dispersion. We propose a stable and economy passive dispersion compensation method to completely cancel out the static second-, third- and especially fourth-order dispersion by inserting a grism pair into the standard chirped-pulse amplification system between the stretcher and the compressor. The best dispersion compensation condition would be achieved by optimizing both the grism pair and the compressor. Compared with the recent passive dispersion compensation method, the experiment results show the pulse duration could be further reduced from 35 fs to 28 fs, the peak intensity of the compression pulse could be increased by 1.25 times, and the spectral phase distortion over the pulse spectrum could be reduced from 12 rad to 4 rad.

The focusing of double-ring-shaped radially polarized ultrashort light pulses by a high-numerical aperture objective is investigated using vectorial Debye theory. After focusing, the double-ring-shaped radially polarized ultrashort light pulses slow down near the focus, and this pulse delay induces pulse compression in the propagation direction. That is, without changing the pulse duration, the spatial pulse length of the ultrashort light pulse is decreased near the focus. The velocity of the longitudinal component of the light pulse near the focus is lower than that of the radial component. The simulation results demonstrate that control of the ratio of the pupil radius to the beam radius affects not only the longitudinal component of the light pulse, but also the velocity and spatial pulse length of the light pulse because of the destructive interference between the longitudinal components of the inner and outer rings of the light pulse.

A resonant microwave pulse compressor with laser triggering of the plasma discharge in its switch was studied for the influence of the unfocused laser beam direction with respect to the RF electric field. The compressor was realized as a rectangular waveguide-based cavity connected to an $H$ -plane waveguide tee with a shorted side arm filled with pressurized helium and pumped by a conventional pulsed $S$ -band magnetron. It was found that neither the direction, nor the intensity of the laser beam significantly affect the compressor output pulse peak power and waveform. Meantime, the delay between the moment of plasma discharge initiation and the appearance of the microwave output is shorter and the time jitter for this delay is smaller if the laser beam is directed along the RF electric field. The same effect was observed when increasing the intensity of the laser beam. Time-resolved optical emission spectroscopy was used to evaluate the plasma density, and numerical simulations of the RF energy release from the system with the appearance of plasma showed a good agreement with the experimentally obtained characteristics of the plasma and microwave output pulse.

We investigate the propagation characteristics of a pulse laser in a time-of-flight laser range finder (TOF-LRF) system with variations in atmospheric conditions, such as temperature, pressure, relative humidity, and the concentration of $CO_2$ . The measurement error of distance related with the group velocity change in the TOF-LRF system is analyzed by considering the refractive index of the standard atmosphere with variations in atmospheric conditions. The dependence of the pulse width broadening induced by chromatic dispersion of the standard atmosphere on the operating wavelength and the initial pulse width of the light sources is discussed. The transmission of air with variations in the relative humidity or the concentration of $CO_2$ is analyzed by using different values of absorption coefficients depending on the operation wavelength of the light source in the TOF-LRF system.

In this paper, we demonstrate a device that is capable of generating an ultrashort (sub-nanosecond) high power microwave pulse by means of passive pulse compression in a compact reverberant cavity. The long duration input pulse into the cavity is created using time-reversal techniques, which allows the waveform to contain the inverse profile of the cavity phase distortion. When fed back into the cavity, the wave focusing at the output port results in a compressed ultrashort pulse with enhanced peak amplitude. We experimentally demonstrate a pulse compressor consisting of a 0.0074 m 3 cavity capable of generating a 130 picosecond pulse from an input waveform of 300 nanosecond duration with the peak gain of up to 19 dB.

A prism compressor can compensate dispersion of femtosecond light pulses travelling in air for laser ranging. An accurate expression of the group delay dispersion (GDD) of a prism compressor at arbitrary incident angle and at arbitrary incident point is obtained, which is of benefit to finely compensating dispersion of femtosecond pulses. Influences of several parameters on group delay dispersion are analyzed for the active compensation of dispersion of femtosecond pulses. These expressions are convenient to applications of intra- and extra-cavity dispersion compensation of ultra-short laser pulses, as well as fine compensation of satellite laser ranging and laser altimetry.

Theoretical investigation of pulse compression in slot optical waveguide based on nonlinear organic material PTS is presented. Results depict compression of pulse from 1ps to 0.59ps in propagation range of 20 cm at 1550 nm.

We present a stable supercontinuum generation in a YAG crystal, driven by 3 ps pulses at 1030 nm. The supercontinuum is demonstrated to be coherent and compressible by Dazzler and prism compressor to below 15 fs.

The tight focusing of radially polarized ultrashort pulsed laser beam is investigated, based on the Richards–Wolf vector diffraction theory. It is found that pulse delay phenomenon occurs near the focus. This is, near the focus, the ultrashort light pulse slows down. Meanwhile, with the decrease of the velocity the ultrashort pulsed laser beam is compressed in propagation direction. The space compression in propagation direction indicates that, though the pulse duration of the ultrashort light pulse does not change, the spatial pulse length of the ultrashort light pulse is reduced due to the pulse delay phenomenon. It is also shown that the different numerical aperture of the objective exhibits different velocity of the pulse light.

The generalized theory of double-mode electrostatic dispersing prism for time-domain compressing electron pulse is presented. The fundamental difference between the two modes of o mode and e mode lies in the dispersive dependence of electron's time of flight on its initial kinetic energy at prism entrance: the electrons with higher initial axial energy definitely have longer time of flight for o mode, while not the case for e mode, which results from the electron pulse's U-shaped motion in the prism. The dispersive dependence of time of flight constitutes the mechanism of electron pulse compression for each mode. An example is given to demonstrate the issue of parameter choosing for the prism and to verify its tunable performance of compression.

We built an atmosphere dispersion model of femtosecond laser pulses that can calculate temporal pulse width travelling in air. The initial pulse duration of 100 fs can be broadened to 60 ps when propagating 200 km in the atmosphere. An experimental system has been established to compensate the large dispersion propagating 200 km in the atmosphere. The single model fiber (SMF) and the prism pairs were, respectively, used for coarse and fine compensation in the system. The pulse duration was consistently regulated 150 fs by moving the distance of prism pairs. This method can reach submicron resolution for a long distance by means of time of flight measurement.

Spatial and temporal chirp will effects a pulse both in space and in time domains. So effectively controlling and utilizing the spatial and temporal chirp has great significance. In this manuscript, firstly the dispersion properties of the prism pair is theoretical analyzed, and the phase delay second derivative expression of the thin prism is obtained. Then a setup is demonstrated to experimentally investigate the spatial and temporal properties of the femtosecond pulse beam. The spatial chirp and temporal chirp effects on the femtosecond pulse beam are experimentally obtained. Both theoretical analysis and experimental results indicate that the group delay dispersion due to prisms is always negative, and the pulse beam can be compressed or broadened by the prism pair based on changing the prisms referring parameters.

The quest for higher peak focused intensities and better temporal contrast drives one to improve the design of all possible stages of the chirped pulse amplification (CPA) system. In this paper, we have analyzed the role of dispersion and spectral profile on the temporal shape and contrast ratio of the output pulse of a CPA system. The simulations indicate that an initial sech2 or a Gaussian pulse in the CPA system is best for a good contrast ratio. Incorporating a four-grating based pulse compressor in the CPA system improves the contrast as well as provides the flexibility to compensate the dispersion upto the fourth order. The simulations also detail the effect of spectral profile tailoring on the contrast ratio and peak power.

The capability of chirped-pulse compression and beam focusing of an object-image-grating self-tiling grating compressor is demonstrated in an optical parametric chirped-pulse amplification laser for the first time. Probe lasers for tiling error adjustments, which are generally required by the traditional tiled-grating compressor, are not needed in our demonstration any more. With the aid of the double-sized effective optical aperture of the second grating in the compressor, a 490 fs near-transform-limit pulse duration and a 90 μm near-diffraction-limit focal spot are obtained, synchronously, which are very close to the ones achieved by a non-tiled grating compressor with equal-sized individual gratings.

A compact 1064/532-nm diode-pumped pulse-periodic YAG:Nd laser is described. Its parameters are as follows: the wavelength is 1064 nm, the pulse energy is 1.2 J, the pulse duration is 5 ns, the pulse repetition rate is 100 Hz, and the beam divergence is ≤1.6 mrad. The laser light efficiency is 12%, and the full efficiency of the laser system is 4%. Two lasing modes are realized in the laser: at the fundamental frequency and with the frequency conversion into the second harmonic at a wavelength of 532 nm and a pulse energy of 0.3 J.

Dispersion effect on mode-locked ring-type erbium-doped fiber laser was experimentally observed. Cutback method was used on the cavity length to vary the dispersion. Stable pulse trains with 9.27-MHz frequency at optimum pulse duration of 864 fs were achieved when the cavity was composed of 17-m single-mode fiber with 5-m gain medium. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2374–2376, 2015

A tiled grating pulse compressor in a single grating configuration has been investigated. Since it is a folded geometry, there are several geometrical constraints that restrict hard-clip-free recompression of positively chirped pulses. Therefore, the parametric space allowed by the geometrical constraints has been worked out for three geometries. In contrast to other pulse compressor designs, owing to the fact that it involves only one tiled optical surface, the present design has advantages of compact geometry, reduced cost, ease of alignment, and easier maintenance for long term stability. Compression of positively chirped laser pulses of ∼250 ps duration to 350 fs has been experimentally demonstrated.

The problem on propagation of an ultrashort radio pulse is analytically solved. The pulse has an envelope of a general shape and a carrier frequency lying within or near the frequency interval of an isolated spectral line of a resonance-absorbing component of a gaseous medium. The solution is used to analyze the character of dispersion distortions of a biexponential quasi-monochromatic pulse and a biexponential chirp pulse that propagate along near-surface and elevated atmospheric paths. The analysis is performed for a single strong line of water vapor in the millimeter wavelength band with a resonance frequency of 183.36 GHz. It is found that the most pronounced feature of distortions of the quasi-monochromatic pulse is gradual transformation of its one-peak envelope into a set of field maxima of various heights. The number of maxima is determined by the optical depth of a path, and, in all of the considered cases, the precursor of a propagating pulse is not formed.

We demonstrate a 10-GHz quad-wavelength pulse source based on fiber optical parametric oscillator with equally distributed dispersion. By adopting two spools of single-mode fiber inside the cavity with nearly the same dispersion, simultaneous mode-locking at two different wavelengths with the wavelength spacing of around ~ 1.9 nm in the L-band is achieved. Owing to the parametric process between the pump and the two mode-locked signals, two idlers are generated in the S-band with the same wavelength spacing. Hence, simultaneous generation of 10-GHz pulse train at four different wavelengths located in both S-and L-band is obtained. The wavelength of the generated pulse trains can be tuned over 67 nm, from 1504 to 1536 nm and from 1575 to 1610 nm, with the wavelength span of around ~ 106 nm .

A two-grating stretcher is a dispersion delay line that is widely used in chirped pulse amplification for ultrafast laser pulses. If the stretcher consists of two reflecting diffraction gratings with a reflective perfect optical system between them, its dispersion can be calculated by using the concept of a “zero-distance pulse front.” We also use the concept of the “zero-distance pulse front” for characteristics of the aberrations in the real optical system of the stretcher. The similarity of these “zero-distance pulse fronts” allows us to study the influence of aberrations in the real optical system of the stretcher on its dispersion.

Difference frequency generation between broadband visible noncollinear optical parametric amplifier (NOPA) pulses and the fundamental pump laser pulses allows the generation of ultrashort infrared pulses with passively stabilized carrier-envelope phase. A simple prism compressor for the visible NOPA pulses is sufficient to generate few-cycle pulses in the infrared and no additional compression is needed. We theoretically investigate the concept, explain the principles, and demonstrate it for high repetition rate, long pulse durations, and various wavelengths by applying it to a Ti:sapphire and an Yb:KYW-based laser systems. For the latter sub-15 fs phase stable pulses around 1.8 μm with an energy of 100 nJ are obtained at 100 kHz repetition rate.

We experimentally demonstrate direct generation of 51 nJ, 284-fs ultrashort pulses in an all-fiber cavity-optimized erbium-doped laser with a low repetition rate of 2.68 MHz. The conversion efficiency of the laser is about 10%. The laser is mode-locked by nonlinear polarization rotation. Such high energy and ultrashort duration benefits from using large output ratio (90%), elongating the cavity length, dispersion management, and bidirectional high-power pumping in the laser. Further decreasing the net dispersion of the laser by using a dispersion-compensated fiber can reduce the pulse duration to 160 fs. In addition, variation of spectral width due to an invisible filter in the laser is experimentally demonstrated.

We demonstrate pulse laser operation of a 4-cm-long Pr3+-doped fluoride-glass fiber laser pumped by InGaN laser diodes (444 nm) using an acousto-optic modulator. We obtained maximum laser peak power of 105.6 W (2.1 μJ/pulse) with a pulse width of 20 ns at an 8.3-kHz repetition rate for a 607-nm wavelength. Employing a prism tuning cavity, we obtained wavelength tunable Q-switch pulse laser oscillation in the visible region (488–491, 520–526, 601–624, 631–644 nm).

When an ultrashort pulse laser is irradiated into the inside of a permeable medium, the refractive index changes dependently on the electric field strength. As a result, a self-focusing phenomenon occurs and self-focusing can lead to a filamentation. In the light absorption medium, the absorbed light energy changes to the thermal energy after ultrashort pulse laser irradiation. Then melting or partial ablation phenomena occur near the focusing area in the medium. Therefore, internal modification, lap welding of permeable materials and so on can be achieved. In this study, a paraxial wave equation including light absorption term was solved by numerical calculation using the fast Fourier transform for irradiation of a Kerr medium by an ultrashort pulse laser. Using the absorbed energy distribution as the initial condition, heat transfer analysis in the material was conducted. The influences of the nonlinear index intensity coefficient and the absorption coefficient on the temperature distribution in the material were investigated.

New ultrashort pulse laser systems exhibit an ever increasing performance which includes shorter pulses and higher pulse energies. Optical components used in these systems are facing increasing requirements regarding their durability, and therefore understanding of the damage mechanism is crucial. In the ultra-short pulse regime electron ionization processes control the damage mechanisms. For the single wavelength, single pulse regime the Keldysh [1] and the Drude model [2] allow a quantitative description of these ionization processes. However, in this model, the electrical field is restricted to a single wavelength, and therefore it cannot be applied in the case of irradiation with two pulses at different wavelengths. As frequency conversion is becoming more common in ultra-short pulse applications, further research is needed in this field to predict the damage resistance of optical components. We investigate the damage behavior of high reflective mirrors made of different metal oxide materials under simultaneous exposure to ultra-short pulses at the wavelengths 387.5 nm and 775 nm, respectively.

Summary form only given. There has been a drive in recent years to produce ultra-high power short pulses for a range of applications. These high power pulses can be produced by microwave pulse compression. Sweep-frequency based microwave pulse compression using smooth bore hollow waveguides is one technique of pulse compression, however at very high powers this method has some limitation due to its operation close to cut-off. In optimum cases, the frequency at the beginning of an input pulse should be only 0.5-1% above the cutoff frequency. If a Cherenkov type TWT is used to drive the compressor then it is inevitable that the low-frequency part of the amplification band is below the cutoff which then reflected from the compressor back to the amplifier resulting in its possible parasitic self-oscillation. If a relativistic BWO is used as a source of frequency-modulated pulses for a smooth-waveguide compressor, then the necessary frequency sweep that would be required can only be produced by using a difficult-to-realize voltage modulation on the BWO. The two combined problems of wave reflection from a compressor and optimum frequency modulation can be solved using a waveguide with a special helical corrugation of its inner surface. A special helical corrugation of a circular waveguide ensures an eigenwave having a strongly frequency-dependent group velocity far from cut-off, which makes the helically corrugated waveguide attractive for using as a compressor of pulses from very high power amplifiers and oscillators. The results of proof-of-principle experiments and calculations of the wave dispersion using a PIC code are presented. In the experiments a 70 ns 1 kW pulse from a conventional TWT was compressed in a 2 metre long helical waveguide. The compressed pulse had a peak power of 10.9 kW and duration of 3 ns. In order to find the optimum pulse compression ratio the waveguide's dispersion characteristics must be well known. The dispersion of the helix was calculated using the PIC code MAGIC and verified using an experimental technique. For a helical compressor the optimum negative frequency sweep can quite naturally be realized at the falling edge of a relativistic BWO pulse. For example, if a BWO generates hundreds of MW during 50 ns over a voltage drop from 700 kV to 400 kV, this frequency modulated radiation can be compressed up to 10-20 times in power with efficiency higher than 50%. Future work detailing plans to produce short, ultra-high power (multi-GW) pulses discussed.

Ultrashort laser pulse has been widely used in various applications. Its parameters, such as the pulse duration and the spectral bandwidth, should be controlled accurately in order to achieve high spatial and temporal resolution, as well as high local field intensity. In this paper, we have proposed a method to trace the propagation of ultrashort pulses through optical systems, especially the complex optics. The approach, in which both the material’s dispersion and optical aberrations are taken into consideration, is developed based on the geometrical ray-tracing combined with wave theories. This method is validated by simulating the propagation of a femtosecond pulse through a specific practical imaging system. As the numerical result shows that the spatial-temporal performances of pulses are influenced greatly by optical elements, the calibration arrangement is employed to compensate for those undesired distortions. The negative dispersion of the optical grisms (the combination of gratings and prisms) is utilized in the calibration process to offset the positive dispersion introduced by lenses. The final result shows effectiveness of the correction.

Spectrum broadening by self-phase modulation (SPM) may be used for increasing PW-class laser pulse power. The influence of high-order spectral phase on SPM and compression of intensity pulses will be discussed. The results of compression of sub-PW pulses of the PEARL laser will be presented.

The results of pulse compression using different stretcher/compressor configurations of the fiber chirped pulse amplification system are demonstrated.

Pulse stretchers are critical components in chirped pulse amplification (CPA) and optical parametric CPA (OPCPA) laser systems. In CPA systems, pulse stretching and compression is typical accomplished using bulk diffraction gratings; however integrated devices such volume or fiber Bragg gratings can provide similar optical performance with significantly smaller footprint and simplified alignment. In this work, we discuss the use of such integrated devices to stretch a 100 fs pulse to 400 ps with customized third order dispersion for use in a multi-TW Ti:Sapphire system as well as integrated optics to control the pulse duration in pump lasers for OPCPA systems.

We demonstrate the utility of an intracavity Martinez compressor with a 71 fs normal dispersion mode-locked Yb:fiber laser. The compressor provides spectral filtering and tunable dispersion compensation from normal to anomalous with simple components.

We demonstrate synchronous dual-wavelength pulse generation in a CNT modelocked Er fiber laser with reduced dispersion based on polarization-dependent spectral filtering, and four-wave mixing between the synchronized pulses is observed.

Methods of wavelength tuning of a polycrystalline Cr2+ : ZnSe laser pumped by a repetitively pulsed Tm : YLF laser (pulse duration ~100 ns, pulse repetition rate 3 KHz) are studied. With the use of a prism selector, the laser wavelength was tuned within the range of 2070 – 2400 nm at a linewidth of 11 nm for a SiO2 prism and 30 nm for a CaF2 prism. The use of a Lyot filter made it possible to tune the Cr2+ : ZnSe laser wavelength (with replacement of the cavity mirrors) within the spectral ranges of 2130 – 2400 and 2530 – 2750 nm at a linewidth of 4 nm.

Ultrashort pulse laser heating of a germanium nanofilm was simulated using a combined continuum–atomistic method that couples the molecular dynamics and a self-consistent energy model for ultrafast laser–semiconductor interaction. Both a single pulse and a pulse burst were considered. To accurately describe laser energy deposition, the transient optical properties were computed based on the Drude formula. It was found that for a single pulse at low fluence (e.g., 0.02 J/cm2), the pulse duration had little impact on the lattice temperature response. In contrast, a higher lattice temperature could be obtained for a longer pulse (e.g., 5 ps) at higher fluences (e.g., 0.06 J/cm2) due to lower surface reflectivity. A strong thermal stress wave could be induced by the laser heating, with its maximum compression and tension occurring in the front and rear film regions, respectively. The investigations of laser burst heating revealed that a laser burst not only can retain the advantages of ultrashort pulse lasers...

In chirped pulse amplification, the amplification of an optical pulse in laser amplifying medium is a very important link. After considering dispersion, Kerr nonlinear effect, gain distribution and loss of the medium, the physical model that the optical pulse propagates in the medium has been established, which is suitable for the general situation where the optical pulse propagates in the amplifying medium. Using a split-step Fourier method, the propagation state of a chirped optical pulse in the amplifying medium has been numerically simulated, and the influences of the gain dispersion of the medium and the frequency detuning of the pulse on the optical pulse have been discussed emphatically. The results show that, with the amplification and propagation of the ultrashort chirped pulse in the amplifying medium, gain saturation and Kerr nonlinear effect of the medium will cause distortion of the optical pulse. For the optical pulse with a wideband spectrum, gain dispersion will cause the gain narrowing effect, so it is equivalent to a loss mechanism. The frequency detuning of the optical pulse will cause distortion of the pulse, which can be used to weaken the impact of gain saturation, thus reshaping the optical pulse.

Pulse propagation characteristics at normal-dispersion region in dispersion-flatted-fibers are experimentally investigated by employing the second-harmonic generation frequency-resolved optical gating (SHG-FROG) method. It is found that the experimental results are consistent with the theoretical prediction. The initial optical pulse with negative chirp is compressed for nonlinear effect in the normal-dispersion fiber, and it evolves into near Gaussian pulse. Temporal width of the optical pulse decreases with the increase of the input power and propagation distance. The output pulse width for small dispersion is less than that for great dispersion at the same input power. The spectrum of the output pulse is still symmetrical about the central wavelength, and is broadened with the increase of input power. The spectral width of the output pulse is much wider than the input spectral width.

This paper presents the Variable Wavelength Interferometry (VAWI) technique, its applications and expected research potential of this system equipped with a femtosecond laser. The system is configured for observation and measurement of local optical parameters modified by a high power laser pulse. The VAWI measurement technique has a unique feature that can visualize and enables investigation of the immediate matter response to a single high power laser pulse just in the pulse area, which can locally modify dielectric and optical parameters of matter along the propagation path. It affects the dielectric tensor, refractive indices and it may induce birefringence. The high power laser pulse is responsible for the nonlinear effects in the optical materials like crystals, photonic crystals, optical fibers etc. The VAWI provides the ability to measure very accurately the above optical parameters along the laser pulse propagation path and neighboring regions in the VIS-NIR spectral ranges.

A new method to measure the spectrum of a pulse light was developed.As the pulse width could be broaden due to the dispersion when a pulse light passed through the optical fiber,the calibration and measurement were proposed to correct and recover the broaden waveform to obtain the real spectrum of a pulse light source.In calibration,the time response function of measuring system was gotten with a ps laser firstly;then the group refractive indexes at different wavelengths were obtained by measuring the time delay of given wavelengths;finally,the relative attenuation index of each wavelength in optical fiber was given by measuring the spectral attenuation.On the basis of the calibration results mentioned above,broaden waveform was recovered by the digital deconvolution,time delay and attenuation.The pulse spectrum of a red scintillator was measured with this method.Results demonstrate that the difference of the center wavelength of the scintillator given by this method and other methods is less than 2 nm,which shows the spectra of pulse light can be measured based on fiber dispersion when the pulse width is much less than its dispersion.

By means of Collins diffraction integral, the propagation expression of an ultrashort laser pulse passing through a spatial filter is derived. The effects of the magnification of spatial filter on pulse broadening and distortion of pulse-front for the ultrashort optical pulse are analytically deduced and numerically simulated. It is found that pulse broadening and propagation time difference of a laser pulse getting through spatial filter is proportional to the magnification. As a conclusion, in an ultrashort pulse laser system with a large aperture, the effect of pulse broadening and distortion of pulse-front should be considered.

Shaping and filtering of ultrashort pulsed beam at 1.06um by using multilayer volume holographic gratings (MVHGs) is analyzed. The modified multilayer coupled wave theory used to analyze the Bragg diffraction of a system of MVHG is derived. The spectral intensity distributions of the diffracted beam are calculated. The diffraction bandwidth, diffraction pulse duration and the total diffraction efficiency of the filter are also analyzed. Control of the optical pulse shape is accomplished by adjusting the width of the intermediate layer of an optical filter of MVHGs. This pulse shaping technique will be useful in the optical communication and optical computing systems.

The hollow-core fiber structure influence of few-cycle pulse compressor on pulse contrast is investigated experimentally. It is found that a periodic structure of pulses at the tail of the main pulse extended hundreds of picoseconds away. It can be due to the fiber structure and could be eliminated by modifying the structure.

The physical model for the optical pulse propagating in the amplifier has been established. Within the normal dispersion region of the fiber, the evolution of the optical pulse in the amplifier has been simulated numerically, and the influence of gain dispersion on the propagation characteristics of the pulse has been discussed emphatically. The results show that, during the propagation of the ultrashort optical pulse in a distributed fiber amplifier, group velocity dispersion and Kerr nonlinear effect will affect the pulse profile and spectrum. For the ultrashort optical pulse with a wideband spectrum, the influence of gain spectrum on the propagation characteristics of the optical pulse, in essence, is that of gain dispersion, which is equivalent to a loss mechanism and will generate gain narrowing effect, so it should be considered in the design of an amplifier system.