Characterization of ultra-weak fluorescence using picosecond non-collinear optical parametric amplifier

We report a technique for characterization of ultra-weak fluorescence based on a 355-nm pumped picosecond non-collinear optical parametric amplifier (OPA). In the experiment, we effectively reduced the strong super-fluorescence background by using a series of methods. With the picosecond OPA as the pre-amplifier and the gating pulse, the decay of the fluorescence of Rhodamine 6G dye in ethanol was measured and the fluorescence lifetime was found to be about 941 ps. The gain factor of this parametric fluorescence amplifier was measured to be ∼4.2 × 10⁶, while the energy detection limit was ∼160 aJ per pulse within a 15-ps gating pulse.     

High repetition rate picosecond LiNbO_3 THz parametric amplifier and parametric gain

A high repetition rate, picosecond terahertz(THz) parametric amplifier with a LiNbO_3(LN) crystal has been demonstrated in this work. At a 10 k Hz repetition rate, a peak power of 200 W and an average power of 12 μW have been obtained over a wide range of around 2 THz; at a 100 k Hz repetition rate, a maximum peak power of 18 W and an average power of 10.8 μW have been obtained. The parametric gain of the LN crystal was also investigated, and a modified Schwarz–Maier model was introduced to interpret the experimental results.     

High-energy picosecond single-pass multi-stage optical parametric generator and amplifier

We demonstrate a new management of multi-stage optical parametric generator(OPG)and amplifier(OPA)to obtain high-energy picosecond sources with high beam quality.The setup of multi-stage OPG-OPA requires mode-matching between the pump beam and the stable mode of the OPG-OPA.In a proof-of-principle experiment,the single-pass multi-stage OPG-OPA consists of three walk-off compensated KTP crystal pairs and two lenses,pumped by an 86 ps,1064 nm 10 kHz picosecond laser.The signal light at~1.77μm has an average output power of 502 mW with record energy up to 50.2μJ.The beam quality factor of the signal light can be improved toM²_x ×M²_yafter filtering out about 40%signal power.To the best of our knowledge,it is the first picosecond single-pass multi-stage OPG-OPA pumped at kHz regime.     

High-power picosecond mid-infrared optical parametric amplifier for infrared Raman spectroscopy

A high-power (50-MW), kilohertz, picosecond, mid-IR optical parametric amplifier that is pumped by an amplified Ti:sapphire laser and also produces a fixed-frequency visible pulse is described. Mid-IR pulse energies of 40-55 microJ with 0.6-0.8-ps durations and 35-cm (-1) bandwidths are reported in the 3650- 2800-cm (-1) range. The combination of picosecond mid-IR and visible pulses is useful for two-color spectroscopies, which require simultaneous time and frequency resolution. To illustrate the above, we present vibrational relaxation data for the polyatomic molecule nitromethane, using time-resolved infrared Raman spectroscopy.     

Compact high gain double-pass optical parametric chirped pulse amplifier

A novel double-pass noncollinear optical parametric chirped pulse amplifier based on an Yb³⁺-doped passively mode-locked fiber laser has been demonstrated in this paper. The signal was double-pass amplified in a single nonlinear crystal by a long pump pulse, and the signal and pump pulses of each pass were completely phase matched in the plane of the maximum effective nonlinearity. Net saturated gain of 2×10⁶ was achieved and the superfluorescence was suppressed by increasing the overlap time between the signal and pump pulses.     

An optical up-conversion light gate with picosecond resolution

Up-conversion (or optical mixing) of light was used to measure the duration of subnanosecond optical pulses.     

Detection of scattered light pulses at femto-Joule level by using a picosecond BBO optical parametric amplifier

We report a technique for detecting weak scattered light pulses based on a 532 nm pumped picosecond β-barium-borate collinear optical parametric amplifier. The measured maximum slope gain factor of the amplifier was found to be around 10⁷, and the energy detection limit was of the order of fJ/pulse for the signal of 730 nm and the idler of 1.5 μm at a pumping intensity of 2.83 GW/cm². The linearity of the gain for this amplifier was found to be excellent for a seeding level of lower than 420 fJ per pulse. The maximum gains and the energy detection limits for the scattered light pulses from various scattering targets were found to be poorer than that from the reflective mirror, owing to the degraded beam quality and the depolarization of the scattered light. A reduction of the maximum gain for the scattered light with the increase of the angle of incidence, which causes pulse broadening and reduces the photon flux of the signal, was investigated. The feasibility of detecting weak scattered light in the infrared by using idler-to-signal frequency up-conversion was also demonstrated, in which the infrared seeder located in the idler branch of the amplifier was injected as the seeding beam and was then parametrically up-converted into the visible signal branch, with an even higher gain.     

Signal wavelength dependence of gain saturation in a fiber optical parametric amplifier

Signal gain-saturation characteristics in a fiber optical parametric amplifier are described. Experiments and calculations for the high-gain-saturation region are presented in which the direction of optical power transfer, which is from the pump to the signal and the idler in the unsaturated region, becomes reversed at high-signal-input powers. It is shown that the signal gain soon saturates for signal wavelengths far from the pump. This wavelength dependence is explained by the power-dependent phase mismatch and its behavior in the high-signal-input region.     

Broadband noncollinear optical parametric amplifier using a single crystal

A noncollinear optical parametric amplifier in which blue pump pulse generation as well as parametric amplification takes place in the same nonlinear crystal is presented. Broadband spectra tunable throughout over 100 nm in the visible were generated in a simple setup. The green output pulses were compressed to 65 fs, and efficiency (IR-to-visible) of 1.8% was achieved.     

Group-velocity-dispersion-compensated femtosecond optical parametric amplifier

A tilted pulse front geometry is known to allow group-velocity-dispersion (GVD) compensated propagation of short pulses of different wavelengths in dispersive media. This scheme is shown to be applicable to an optical parametric amplifier (OPA) pumped at 450nm. A numerical calculation shows that a certain combination of the tilt of the pulse front and the angle between the interacting beams provides optimum GVD compensation for each wavelength. The parameters providing broadband tunability are identified. The tunability of the GVD-compensated OPA pumped with 55fs pulses was experimentally demonstrated between 545nm and 645nm. This revised version was published online in November 2006 with corrections to the Cover Date.     

Amplification of fluorescence using collinear picosecond optical parametric amplification at degeneracy

We demonstrate the output characteristic of broadband parametric amplification of incoherent light pulses in a 355-nm pumped degenerate picosecond optical parametric amplification with either saturated or unsaturated amplification.The optical parametric amplifier is seeded by the fluorescence generated in a solution of pyridine-1 dye in ethanol.With the saturated amplification,we can obtain high energy incoherent light pulses,whose full width at half maximum bandwidth varies from 16 nm to 53 nm for the different phase matching angles near degeneracy.Moreover,the unsaturated bandwidth of the amplified pulses fits well to the calculated result at degeneracy.Selecting s-polarized fluorescence with a Glan-Taylor prism,the maximum bandwidth of the amplified fluorescence is found to be 59 nm for a purely s-polarized seed.The maximum output energy is 0.67 mJ for the optical parametric amplifier.By using an optical filter and compressor,the generated high energy incoherent light has great potential as the incoherent pump,signal or idler wave of a parametric down-conversion process,so that a wave with a high degree of coherence can be generated from an incoherent pump light.     

基于LBO晶体的高效千赫兹皮秒量级光学参量产生器

本文所述的光学参量产生器(OPG)是基于高效的三硼酸锂(LBO)晶体,由倍频半导体激光Nd:YVO4振荡放大(MOPA)系统作为泵浦辐射源.根据Boydand Kleinman理论:聚焦效应可以使泵功率密度为50 GW/cm2,这远远低于LBO晶体的损伤阈值80 GW/cm2,发生简并时其总的转换效率可达到72%.当整体转换效率达到50%时,OPG可调谐范围的范围可以从760 nm到1770 nm.当转换效率低于40%(M21.3)时,光束质量是非常优良的.通过种子光注入OPG,10 nm(RMS)谱线带宽可以被缩窄.种子激光注入可以表示为波长922.54 nm的信号.30 n W种子CW具有足够的功率可以将光谱宽度减少为0.1 nm(RMS).测量种子光注入OPG脉冲持续时间为9 ps(FWHM).这会导致时间带宽积为1.30,这是sech2型脉冲理论极限为0.315的4.1倍.     

Simultaneous parametric generation and up-conversion of entangled optical images

A quantum theory of parametric amplification and frequency conversion of an optical image in coupled nonlinear optical processes that include one parametric amplification process at high-frequency pumping and two up-conversion processes in the same pump field is developed. The field momentum operator that takes into account the diffraction and group velocities of the waves is used to derive the quantum equations related to the spatial dynamics of the images during the interaction. An optical scheme for the amplification and conversion of a close image is considered. The mean photon number density and signal-to-noise ratio are calculated in the fixed-pump-field approximation for images at various frequencies. It has been established that the signal-to-noise ratio decreases with increasing interaction length in the amplified image and increases in the images at the generated frequencies, tending to asymptotic values for all interacting waves. The variance of the difference of the numbers of photons is calculated for various pairs of frequencies. The quantum entanglement of the optical images formed in a high-frequency pump field is shown to be converted to higher frequencies during the generation of sum frequencies. Thus, two pairs of entangled optical images are produced in the process considered.     

Hybrid flat gain C-band optical amplifier with Zr-based erbium-doped fiber and semiconductor optical amplifier

An efficient gain-flattened C-band optical amplifier is demonstrated using a hybrid configuration with a Zirconia-based Erbium-doped fibre (Zr-EDF) and a semiconductor optical amplifier (SOA). The amplifier utilizes a two-stage structure with a midway isolator to improve flat gain characteristic and reduce noise figure. At input signal power of −30 dBm, a flat gain of 28 dB is obtained from wavelength region of 1530 to 1560 nm with gain variation of less than 4 dB. The noise figure is maintained below 11 dB at the flat-gain region. This amplifier has the potential to be used in the high channel count dense wavelength division multiplexing system due to its simplicity and compact design.     

增益半导体光放大器的特性

为满足半导体光放大器（SOA）在光纤到户FTTH系统接入网中的广泛应用,提出了基于光纤光栅外腔反馈型GC-SOA结构的全光增益机制,窄线宽激光光源经可变衰减器、隔离器和光纤光栅注入到SOA中,SOA的输出光经隔离器和光纤光栅送至光谱分析仪,通过光纤光栅反馈输入SOA形成钳制激光。对GC-SOA的阈值特性、增益特性及开关特性进行分析,结果表明:当注入电流小于GC-SOA的阈值电流时,增益随注入电流的增加而增加;当注入电流大于GC-SOA的阈值电流后,其增益不再随注入电流的变化而变化,实现了SOA的增益稳定,使SOA的饱和输出功率得到了提高。     

Efficient injection-seeded kHz picosecond LBO optical parametric generator

We report a highly efficient optical parametric generator (OPG) in lithium triborate (LBO). A frequency-doubled passively mode-locked diode-pumped Nd:YVO₄ oscillator amplifier (MOPA) system is used as the pump radiation source. Focussing according to the theory of Boyd and Kleinman leads to a pump power density of 50 GW/cm², which is well below the damage threshold of LBO of 80 GW/cm². The overall conversion efficiency reaches a value of 72% measured at degeneracy. The tuning range of the OPG ranges from 760 nm (signal) to 1770 nm (idler) when referring to an overall conversion efficiency of 50%. The beam quality is excellent for conversion efficiencies below 40% (M ²<1.3). The typically 10 nm (RMS) broad spectrum can be narrowed by injection seeding the OPG. Injection seeding is demonstrated for a signal wavelength of 922.54 nm. A seed cw power of 30 nW is sufficient to reduce the spectral width to 0.1 nm (RMS). The measured injection-seeded OPG pulse duration is 9 ps (FWHM). This results in a time–bandwidth product of 1.30, which is 4.1 times the theoretical limit of 0.315 for sech²-shaped pulses.     

High-energy, diode-pumped, picosecond Yb:YAG chirped-pulse regenerative amplifier for pumping optical parametric chirped-pulse amplification

A diode-pumped, cryogenic-cooled Yb:YAG regenerative amplifier utilizing gain-narrowing has been developed. A 1.2-ns chirped-seed pulse was simultaneously amplified and compressed in the regenerative amplifier, which generated a 35-ps pulse with ~8-mJ of energy without a pulse compressor. Second-harmonics of the amplified pulse was used to pump picosecond two-color optical parametric amplification.     

High-peak power multi-wavelength picosecond pulses generated from a BaWO4 Raman-seeded optical parametric amplifier

We report the generation of high-peak power multi-wavelength picosecond laser pulses using optical parametric amplification (OPA) in BBO seeded with pulses generated in a 5-mm length BaWO₄ crystal by stimulated Raman scattering of 18-ps laser pulses at 532 nm. The maximum output energy of the amplified first-Stokes component at 559.7 nm was about 1.76 mJ. The corresponding maximum peak power, pulse duration and spectral line width were measured to be 117.3 MW, 15 ps and 18.0 cm⁻¹, respectively. The multi-wavelength picosecond laser pulses were in the visible and near infrared ranges. Using this Raman-seeded OPA technique, the beam quality of the stimulated Raman scattering pulses can be improved.     

Tandem chirped quasi-phase-matching grating optical parametric amplifier design for simultaneous group delay and gain control

We present a broadband optical parametric amplifier design using tapered gain and tandem chirped quasi-phase-matching gratings to obtain flat gain and group-delay spectra suitable for applications such as ultrashort-pulse amplification and fiber-optic communication systems. Although a tapered-gain amplifier consisting of a single chirped grating can provide constant gain over a wide frequency range, it cannot be used to control the group delay across the spectrum. We propose controlling both the gain and the group delay profiles using a two-stage amplifier configuration, in which the idler of the first is used as the input signal of the second.     

Continuous-wave fiber optical parametric wavelength converter with +40-dB conversion efficiency and a 3.8-dB noise figure

We have obtained 40 dB of internal (on-off) conversion gain and a sub-4-dB noise figure (NF) with a continuous-wave (cw) fiber optical parametric wavelength converter. To our knowledge, this is the lowest NF reported for any cw wavelength converter. We have also investigated the properties of NF versus signal input power and pump power.