Femtosecond Optical Parametric Amplifier Research Articles

Group velocity self-matching in noncollinear optical parametric generation with a type-Ⅰ phase-matched BBO crystal

Noncollinear parametric superfluorescence (NPS) is obtained in the visible regio n by pumping a type-Ⅰ phase-matched BBO crystal with the second harmonic of an amplified Ti:sapphire laser at 1kHz repetition rate. The variation of the noncol linear angle and the wavelength at the peak intensity of the NPS with the phase- matched angle is studied, and the variations of the group velocity mismatch (GVM ) with the noncollinear angle and the phase-matched angle in the three-wave inte raction is calculated theoretically. The results indicate that the type-Ⅰ phase -matched NPS ring is centrosymmetric with respect to the pump beam on the observ ation screen. Along the NPS direction at the peak intensity, the GVM is minimal and the effective interaction length is maximal for the three waves. The angular distribution of the NPS intensity is ascribed to phase velocity and group veloc ity self-matching among interacting pulses. The theory and the experiment provid e an ideal geometrical model for reducing the GVM between three waves, and provi de a theoretical guidance and experimental verification for obtaining parametric pulses with higher gain and shorter duration in femtosecond optical parametric amplification.

Idler second harmonic generation in femtosecond BBO optical parametric amplification

For femtosecond optical parametric amplification (OPA) pumped with a 400nm blue laser, limited by phase-matched condition and nonlinear crystal transparent range, the tuning range of the output parametric laser is restricted, and the blue and the near UV lasers with wavelength less than 460nm are difficult to obtain. In our experiment, we adopted the second harmonic of a Ti:sapphire nine-pass chirp pulse amplifier at 1kHz repetition rate as the pump beam, and the white- light supercontinuum as the seed beam; thus, by a type-Ⅰ noncollinear phase-mat ched broad bandwidth β-BaB2O4 (BBO) OPA, with certain exp erimental paramete rs, the amplified signal beam from 530nm to 810nm and the idler beam from 81 0nm to 17μm were obtained; at the same time, the idler second harmonic fr om 410nm to 700nm was obtained also. The idler second harmonic was cascaded with the idler beam, its pulse energy was 26μJ and the conversion efficienc y was greater than 5%. Therefore, femtosecond pulses tuned continuously from 410 nm to 810nm can be obtained by the BBO OPA with a single crystal only, there by a useful source is provided for more investigations and applications. In this paper, we also have theoretically analyzed the generation condition of the idle r second harmonic for femtosecond OPA.

Compensation of group velocity mismatch for optical parametric amplification in BBO type-I phase-matched configuration

A method that compensates completely the group velocity mismatch between three w aves for femtosecond optical parametric amplification (OPA) in BBO type-I phase- matched configuration is presented by combining noncollinear configuration with tilting pump wave front. When the group velocities of the three waves are matche d, the variations of the noncollinear angle, the phase-matched angle and the pum p wave front tilt angle with the signal wavelength are calculated theoretically, and the effects of the pump beam size and the spatial walk-off length are analy zed. The results indicate that this method not only can achieve maximal parametr ic bandwidth, but also can match completely the group velocities between three w aves for femtosecond OPA. In addition, with increasing parametric gain, it is ve ry importance to appropriately choose the pump beam size and the nonlinear cryst al length.

A CW seeded femtosecond optical parametric amplifer

A CW seeded femtosecond optical parametric amplifier, a compromise between OPG/OPA and strongly seeded OPA configurations, has been demonstrated. An independent CW Nd: YAG laser with sub-watt power decreases the pump threshold of the OPA and improves the stability of the output pulses considerably. Output signal energies as high as 30 μJ with pulse durations less than 250 fs near 1 μm are reported. from this two-stage device.

Tunable femtosecond optical parametric amplifier with weak CW seeding

A tunable femtosecond optical parametric amplifier with weak CW seeding, a compromise between OPG/OPA and strongly seeded OPA configurations, has been demonstrated. A CW Nd:YVO4 laser with sub-watt power helps to saturate and stabilize the output pulses from the OPA, and meanwhile a direct tunable range from 1.01 to 1.08 μm at the signal wavelength is obtained. Output signal energies as high as 30 μJ with pulse durations less than 250 fs within the tuning range are reported from this two-stage device.

Experimental and theoretical analysis of white-light seeded, collinear phase-matching, femtosecond optical parametric amplifiers

We report a high-power, kilohertz, collinear phase-matching ultrafast optical parametric amplifier (OPA) that is capable of producing 70-μJ, ~150-fs infrared laser pulses at wavelengths ranging from 2.9 to 4.0 μm. The OPA system was seeded with a broadband white-light continuum, which was carefully characterized experimentally. The retrieved electric field of the white-light seed pulse was incorporated in a simulation. The simulated results almost perfectly matched the experimental results of our OPA system. We used the simulation further to investigate the interplay between material dispersion and optical nonlinearity in ultrafast OPA systems and to examine the role of white-light seed pulses in such systems.

A CW seeded femtosecond optical parametric amplifier

A CW seeded femtosecond optical parametric amplifier, a compromise between OPG/OPA and strongly seeded OPA configurations, has been demonstrated. An independent CW Nd︰YAG laser with sub-watt power decreases the pump threshold of the OPA and improves the stability of the output pulses considerably. Output signal energies as high as 30 mJ with pulse durations less than 250 fs near 1 mm are reported from this two-stage device.

Application of the solid solution CdxHg_1–xGa_2S_4 as a nonlinear optical crystal

We review the optical properties of the mixed crystal Cd(x)Hg(1-x)Ga(2)S(4) , propose three potential applications to which various physical properties can be tailored, and present experimental results of femtosecond optical parametric amplification in the mid IR from 5.5 to 8mum with 1.25-mum pumping by a 1-kHz Cr:forsterite regenerative amplifier.

Dot patterns from second-harmonic and sum-frequency generation in polycrystalline ZnSe

During a comparative study of second-harmonic generation (SHG) and sum-frequency generation (SFG) in single-crystal and polycrystalline ZnSe, the polycrystalline material showed a dot pattern in the SHG as well as in the SFG output. No such pattern was found in the output from the single-crystal ZnSe sample. The second-harmonic and also the sum-frequency dot pattern, resembling a diffraction pattern, could be observed over a wide tuning range of the fundamental beam, between 1.1 and 1.6 μm, generated by a femtosecond optical parametric amplifier. The size of the observed pattern is dependent on wavelength and the dots show a characteristic polarization.

Noncollinear optical parametric amplifiers with output parameters improved by the application of a white light continuum generated in CaF 2

We report the drastic improvement of output parameters of femtosecond noncollinear optical parametric amplifiers by applying supercontinuum seed pulses generated in CaF 2 instead of sapphire and imaging via all reflective optics. Features of the setup are broad amplification bandwidths up to 310 THz (470–910 nm), an almost Gaussian beam profile, a divergence with M 2 factor of less than 1.4, pulse to pulse energy fluctuations of less than 2.5% and compressibility of the pulses down to 16 fs. The high intensity of the supercontinuum seed pulse (80 nJ) yields a quantum efficiency for the conversion of pump to signal of more than 30%. Even for short wavelengths e.g. at 470 nm pulse energies above 30 μJ were obtained for 110 μJ of 400 nm pump light.

Efficient femtosecond optical parametric generator with a birefringent delay compensator

A novel method based on a birefringent crystal is presented to compensate for the group-velocity mismatch between a femtosecond pulsed pump and the signal or idler in an optical parametric generator (OPG). With a thin calcite plate inserted between two beta-barium borate crystals for synchronization, an efficient four-pass OPG pumped by a frequency-doubled ~200-fs Ti:sapphire laser is obtained. The conversion efficiency is almost doubled throughout the whole tunable region compared with a conventional OPG pumped at the same power density, indicating that the total conversion efficiency of femtosecond optical parametric amplifier system can be raised significantly by use of this new four-pass OPG to generate the seed.

Optical parametric generation of femtosecond pulses up to 9 μm with LiInS2 pumped at 800 nm

We demonstrate direct access to the 4.8–9 μm spectral region with 800 nm, 1 kHz pumping of a femtosecond optical parametric amplifier based on the wide-gap wurtzite-type LiInS2. LiInS2 did not exhibit two-photon absorption at 800 nm and seems applicable at this pump wavelength with intensities of the order of 100 GW/cm2 for down-conversion of high energy ultrashort pulses up to its mid-IR edge at ≈12 μm.

KTiOPO4, KTiOAsO4, and KNbO3 crystals for mid-infrared femtosecond optical parametric amplifiers: analysis and comparison

We have designed a simple mid-IR femtosecond OPA seeded by a white-light continuum and delivering very stable, largely tunable and energetic output pulses. This OPA requires fewer than 200 μJ of 120-fs Ti:sapphire pump pulses as energy. This system allowed us to experimentally compare the performances of potassium crystals (KTP, KTA, and KNbO3) for the generation of up to 100-fs Fourier-transform-limited pulses tunable in 1–4.6 μm mid-IR wavelengths.

Laser-diode-seeded single and double stage femtosecond optical parametric amplification in the mid-infrared

Tunable mid-infrared pulses are generated with a MgO:LiNbO3-based traveling-wave optical parametric amplifier in single and double stage operation regime pumped by a 1-kHz Ti:sapphire regenerative amplifier system. For the first time to our knowledge a pulsed laser diode is successfully used in the femtosecond regime as a compact seed source at the signal wavelength where the tunability of the generated idler pulses can be realized by tuning the seed wavelength. Almost transform limited mid-infrared pulses as short as 130 and 160 fs with pulse energies as high as 5 and 15 μJ are produced near 3.5 μm by the single and double stage scheme, respectively. The pulse to pulse fluctuations in both cases do not exceed 2% which corresponds to the stability of the pump source.

Efficient femtosecond traveling-wave optical parametric amplification in periodically poled KTiOPO_4

We report, for the first time to our knowledge, high-power femtosecond traveling-wave optical parametric amplification by use of periodically poled KTiOPO(4) . With a single pass through a 4-mm-long sample of 1.23-mm thickness we achieved 40% internal conversion efficiency and 5microJ of single-pulse idler energy near 3.8microm , using only 75microJ of energy from the output of a conventional 1-kHz Ti:sapphire regenerative amplifier. The 210-fs-long idler pulses were almost transform limited. We discuss the specific problems encountered in high-power parametric conversion, such as unwanted quasi-phase-matched upconversion processes for polarization configurations that utilize the largest (d(33)) nonlinear coefficient and the related formation of color centers (gray tracking) in KTiOPO(4) .

Laser-diode-seeded operation of a femtosecond optical parametric amplifier with MgO:LiNbO_3 and generation of 5-cycle pulses near 3 μm

A high-power traveling-wave optical parametric amplifier based on MgO:LiNbO3 that is capable of producing extremely short pulses in the 3-µm spectral range when pumped by a femtosecond Ti:sapphire amplifier near 800 nm has been developed. With seeding by 1-ns pulses from a low-power Q-switched microlaser, we demonstrate idler tunability between 3.1 and 3.9 µm at >10-µJ pulse energy and <200-fs pulse duration. The maximum internal conversion efficiency is 40% for a single pass. The extremely high gain factors achieved permit a more compact solution for the seed source, and we also report on successful seeding with a pulsed laser diode in the femtosecond regime, achieving 5-µJ pulse energy and 130-fs pulse duration near 3.5 µm. We have produced nearly transform-limited 50-fs, 2-µJ pulses near 3 µm with a 1-mm-thick MgO:LiNbO3 sample by adding a second pass and employing sub-30-fs pumping.

Interferometric nonlinear mixing in multiple-pass femtosecond optical parametric amplification

We demonstrate that in multi-stage optical parametric amplifiers, spatial and temporal overlap of all products and pump on subsequent passes lead to strongly phase-dependent conversion, which has important consequences for output noise and beam profile characteristics. We verify a simple method to avoid this interferometric process.

Femtosecond traveling-wave optical parametric amplification in MgO:LiNbO_3

A mid-infrared femtosecond optical parametric amplifier tunable in the chemically important spectral region between 3.1 and 3.9 mum (at >10-muJ idler pulse energy) has been constructed on the basis of MgO:LiNbO(3) with 7% doping. With femtosecond pumping near 800 nm (Ti:sapphire regenerative amplifier) and narrow-band (long-pulse) seeding, this simple single-stage device provides maximum conversion efficiencies of 40% and exhibits extremely low seed threshold (<10-mW peak seed power for >1-muJ idler output). The generated idler pulses are almost transform limited with <200-fs pulse duration. The pulse-to-pulse fluctuations reproduce the stability of the pump source at 1-kHz repetition rate.

Highly efficient, widely tunable, 10-Hz parametric amplifier pumped by frequency-doubled femtosecond Ti:sapphire laser pulses

We report a 10-Hz, highly efficient, widely tunable (from the visible to the IR), broadband femtosecond optical parametric generator and optical parametric amplifier (OPA) in BBO, LBO, and CBO crystals pumped by the frequency-doubled output of a regeneratively amplified Ti:sapphire laser at 400 nm. The output of the system is continuously tunable from 440 nm to 2.5 microm with a maximum overall efficiency of approximately 25% at 670 nm and an optical conversion efficiency of more than 36% in the OPA stage. The effects of the seed beam energy, the type of the crystal and the crystal length, and the pumping energy of the output of the OPA, such as the optical efficiency, the bandwidth, the pulse duration, and the group velocity mismatch between the signal and the idler and between the seeder and the pump, are investigated. The results provide useful information for optimization of the design of the system.

Automatic time delay optimization between the pump and seed pulses of a broadly tunable femtosecond optical parametric amplifier

We propose a scheme for optimizing the time delay between the pump and seed pulses of an optical parametric amplifier (OPA) over a large spectral range. The efficiency of this method is demonstrated for a femtosecond BBO parametric amplifier seeded with a white-light continuum pulse. The error signal used for intensity stabilization results from a modulation of the temporal delay between the pump and the continuum pulses and phase-sensitive detection of the amplified signal. It allows us to lock the delay to the position that maximizes the OPA gain.