Achromatic Phase Matching Research Articles

Temperature- and wavelength-insensitive parametric amplification enabled by noncollinear achromatic phase-matching.

Optical parametric chirped-pulse amplification (OPCPA) has been demonstrated to be a promising approach for pushing femtosecond pulses towards ultra-high peak powers. However, the future success of OPCPA strongly relies on the ability to manipulate its phase-matching (PM) configuration. When a high average power pump laser is involved, the thermal effects in nonlinear crystals induce phase-mismatch distortions that pose an inherent limitation on the conversion efficiency. Here, we demonstrate that the noncollinear configuration previously adopted for wavelength-insensitive PM can be employed for temperature-insensitive PM when the noncollinear angle is properly reset. Simultaneous temperature- and wavelength-insensitive PM is realized for the first time by imposing such a temperature-insensitive noncollinear configuration with an angularly dispersed seed signal. Based on the lithium triborate crystal, the proposed noncollinear achromatic PM has a thermal acceptance 6 times larger than that of the conventional wavelength-insensitive noncollinear PM and has a sufficient spectral acceptance to support pulse durations of ~20 fs at 800 nm. These achievements open new possibilities for generating ultra-high peak power lasers with high average power.

The Optical Design of Achromatic Phase Matching System Based on ZEMAX

The system of achromatic phase matching (APM) based on grating pairs is designed by the commercial optical design software ZEMAX. Firstly, we theoretically calculate the theoretical incident angular where each frequency components exactly reaches the phase-matching in nonlinear crystals. Subsequently, the model of APM system is built and optimized in ZEMAX. The results are well in accordance with the theoretical ones. In addition, the effects of grating frequency and aberration produced by the focus lens on APM scheme are analyzed.

Theory of second harmonic generation of ultrashort pulses for collinear achromatic phase matching

Achromatic phase matching (APM), a favorable method in increasing phase matching bandwidth, is explored for second harmonic generation of ultrashort pulses based on a typical grating telescope system. A set of coupled equations incorporating angular dispersion is constructed in the space–time domain. An analytic solution with a pump of tilting pulsed Gaussian beam to the equations is given under the undepleted pump approximation. With the aid of matrix formalism, some properties of the conversion are demonstrated. Though a maximal phase matching bandwidth is obtained, angular dispersion makes the conversion active only around the geometrical focus. Theory shows that APM does not require an overall pulse-front matching in the conversion process.

Gaussian wave-packet reshaping into conical via parametric amplification of the far field

In this paper we propose a method for pulsed conical wave parametric amplification (PCWPA) with subsequent spatio-temporal compression during propagation in free space. It is numerically demonstrated that Gaussian wave-packet can be reshaped into pulsed conical wave (PCW) just by means of lens and nonlinear crystal. We point out that performing the far field amplification of the PCW is the key for generation of localized PCWs with ultrahigh intensities. It allows to form ultra-intense and propagation invariant wave-packets capable to propagate over many Rayleigh range in the desired material. The method exploits achromatic phase matching and empowers the parametric amplification of bandwidths corresponding to few-cycle light pulses with Gaussian temporal spectrum. In contrast to ordinary chirped-pulse amplification technique it does not require a pulse compressor, thus greatly facilitates the parametric amplification of few-cycle light pulses.

Investigation of spectral bandwidth of BBO-I phase matching non-collinear optical parametric amplification from visible to near-infrared

Laser sources which have high power, short time duration and are broadly tunable are needed for the application of ultra-fast lasers. Femtosecond optical parametric amplification (OPA) is one of the most important techniques to produce broadly tunable and several femtosecond laser pulses. To obtain an extremely short pulse, the femtosecond OPA should adequately support a large spectral bandwidth. Ultra-broadband type-I phase matching OPA based on BBO was theoretically investigated. The achromatic phase matching (APM) technology was introduced to femtosecond OPA, and a broadband phase matching condition was given when the signal beams were angularly dispersed. The methods were presented to choose the optimized non-collinear angle and angular dispersion. Effects of non-collinear angle and rate of angular dispersion to the parametric bandwidth were also discussed. The results indicate that a proper non-collinear angle of the non-collinear optical parametric amplifier (NOPA) and getting signal beams dispersed at the right rate in near-infrared conditions can increase the parametric bandwidth dramatically.

Indistinguishability of entangled photons generated with achromatic phase matching

We put forward a method to suppress distinguishing information contained in the frequency spectrum of entangled photon pairs generated in spontaneous parametric down-conversion. The distinguishing information is shown to be suppressed by employing achromatic phase-matching techniques to tailor the group velocities of the generated signal and idler photons, and thus tuning their spectral properties. The method can be implemented in materials and frequency bands where conventional solutions do not hold, and it can benefit from the dispersion cancellation inherent to entangled photons featuring frequency correlation or anticorrelation. The generation of polarization Bell states is discussed.

Engineering the frequency correlations of entangled two-photon states by achromatic phase matching

We put forward a new method to control the spectra of photon pairs generated in parametric downconversion that allows their spectral properties to be tuned from correlation to anticorrelation, including uncorrelation. The method employs tilted pulses and can be implemented in materials and frequency bands for which conventional methods do not hold.

Generation of tunable 7-fs ultraviolet pulses: achromatic phase matching and chirp management

Ultraviolet pulses with a duration of 7 fs are efficiently generated by frequency doubling the output of a noncollinear optical parametric amplifier. The ultraviolet pulses are tunable between 275 to 335 nm. The acceptance bandwidth of the doubling crystal is increased by a factor of 80 through high-order achromatic phase matching. The chirp of the visible pulses and the dispersion introduced along the beam path are compensated partially before and partially after the doubling crystal. For the design of the dispersion management, we investigate the second harmonic generation of pulses with mixed orders of chirp and explicitly discuss the transfer of the spectral phase in frequency doubling. A simple analytic theory is derived that correctly describes frequently observed spectral narrowing effects. We find that chirped SHG avoids spectral narrowing and allows for precompression of dispersion encountered in the ultraviolet beam path. We apply chirped SHG to generate 18.7 fs ultraviolet pulses in an extremely simple setup.

The application of achromatic phase matching in optical parametric chirped-pulse amplification

Optical parametric chirped-pulse amplification (OPCPA) supplies broadband gain for ultrashort pulses. A new theoretic explanation of OPCPA has been obtained by introducing the concept of tilted pulse front in this paper, and the distribution of broadband amplification has been twice expanded by introducing the technology of achromatic phase matching (APM). The prospect of APM in OPCPA has been discussed in detail. Finally, a design for the amplification of chirped pulses at 1600 nm has been firstly proposed and numerically simulated.

Tunable sub-10-fs ultraviolet pulses generated by achromatic frequency doubling.

Tunable UV pulses shorter than 10 fs are generated by achromatic frequency doubling of a noncollinear optical parametric amplifier. With a suitable two-prism sequence we achieve first- and second-order achromatic phase matching and increase the natural bandwidth of the nonlinear crystal by a factor of 80. Extremely broad UV spectra with a Fourier limit of 2.9 fs are generated in a 360-microm-thick beta-barium borate crystal at a conversion efficiency of 20%. We compensate for the angular dispersion and the first-order chirp of the highly stable UV pulses with a second prism sequence and fully characterize the temporal pulse shape with zero-additional-phase spectral phase interferometry for direct electric-field reconstruction (ZAP-SPIDER). Pulses as short as 7 fs are generated by controlling the higher-order chirp with a deformable mirror.

Group-velocity matched second-harmonic generation in tilted quasi-phase-matched gratings

We propose a novel scheme of achromatic phase matching for second-harmonic generation (SHG) in tilted quasi-phase matching gratings. The spectral angular dispersion is introduced in fundamental waves such that each frequency component satisfies the two-dimensional quasi-phase matched condition. This is equivalent to simultaneous quasi-phase- and group-velocity-matched SHG for ultrashort pulses. Equations to describe achromatic conditions are derived and applied specifically to periodically poled lithium niobate (PPLN). The phase-matching bandwidth for 10 mm-long PPLN increases by factors of 110 and 32 at wavelengths of 0.8 and 1.55 μm, respectively, compared with those for the conventional quasi-phase matching.

All-prism achromatic phase matching for tunable second-harmonic generation

Achromatic phase matching (APM) involves dispersing the light entering a nonlinear optical crystal so that a wide range of wavelengths is simultaneously phase matched. We constructed an APM apparatus consisting of six prisms, the final dispersion angle of which was optimized to match to second order in wavelength the type I phase-matching angle of beta barium borate (BBO). With this apparatus, we doubled tunable fundamental light from 620 to 700 nm in wavelength using a 4-mm-long BBO crystal. An analogous set of six prisms after the BBO crystal, optimized to second order in second-harmonic wavelength, realigned the output second-harmonic beams. Computer simulations predict that adjustment of a single prism can compensate angular misalignment of any or all the prisms before the crystal, and similarly for the prisms after the crystal. We demonstrated such compensation with the experimental device. The simulations also indicate that the phase-matching wavelength band can be shifted and optimized for different crystal lengths.

Achromatic phase matching for tunable second-harmonic generation by use of a grism

Achromatic phase matching (APM) involves dispersing the light entering a nonlinear-optical crystal so that a wide range of wavelengths is simultaneously phase matched. Using an APM arrangement consisting of a grism (a grating on the surface of a prism) and three prisms, optimized to match a second-harmonic crystal phase-matching angle versus wavelength to high order, we efficiently doubled tunable fundamental light near 650nm with a bandwidth of >95 nm by use of a 4-mm type I beta-barium borate crystal. APM uses no moving parts, and unlike previous APM designs, ours avoids lenses and hence is easy to align and insensitive to translational misalignment of the beam.

Achromatic phase matching for second harmonic generation of femtosecond pulses

A scheme is proposed by which the phase matching bandwidth can be increased by adjusting higher-order terms in frequency shift in the phase-matching condition. This is achieved by introducing a spectral angular dispersion so that the different spectral components propagate at their phase-matching angles. This is equivalent to canceling the group velocity mismatch. The equations describing the requirements on the angular dispersion are discussed and applied to the particular case of type I phase matching. A possible experimental setup is shown that would meet all the conditions required.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>