Enhancement of terahertz wave generation by cascaded χ^(2) processes in LiNbO_3

Jewariya, Mukesh; Nagai, Masaya; Tanaka, Kōichiro

doi:10.1364/josab.26.00a101

Cited by 87 publications

(51 citation statements)

References 23 publications

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“…In the EO detection, six high-resistivity Si attenuaters were inserted to reduce the field amplitude before the GaP detection crystal. 19 The maximum modulation of the balanced photodetector signals I A and I B measured at the peak THz field, i.e., ͑I A − I B ͒ / ͑I A + I B ͒, is 0.44 with the Si attenuators; this value corresponds to the electric field of 1.2 MV/cm without the Si attenuators. 20 The spectrum in Fig.…”

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confidence: 98%

Single-cycle terahertz pulses with amplitudes exceeding 1 MV/cm generated by optical rectification in LiNbO3

Hirori

Doi

Blanchard

et al. 2011

Applied Physics Letters

786

501

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Using the tilted-pump-pulse-front scheme, we generate single-cycle terahertz ͑THz͒ pulses by optical rectification of femtosecond laser pulses in LiNbO 3 . In our THz generation setup, the condition that the image of the grating coincides with the tilted-optical-pulse front is fulfilled to obtain optimal THz beam characteristics and pump-to-THz conversion efficiency. By using an uncooled microbolometer-array THz camera, it is found that the THz beam leaving the output face of the LN crystal can be regarded as a collimated rather than point source. The designed focusing geometry enables tight focus of the collimated THz beam with a spot size close to the diffraction limit, and the maximum THz electric field of 1.2 MV/cm is obtained. © 2011 American Institute of Physics. ͓doi:10.1063/1.3560062͔Recent successful developments in efficient high-power terahertz ͑THz͒ pulse generation has created many promising applications such as in large-scale object imaging, medical diagnosis and treatment, and remote sensing techniques for security issues.1,2 In addition, intense THz pulses allow for study of unexplored nonlinear phenomena such as coherent THz manipulation of quantum states, 3,4 high-order harmonic generation, 5 nonlinear optical processes, and nonlinear transport phenomena in solids. [6][7][8][9][10][11][12] Since Hebling et al.13 ͑2002͒ proposed a tilted-pumppulse-front scheme for efficient phase-matched THz pulse generation using LiNbO 3 crystals, the technique has been rapidly developing. This technique has demonstrated the possibility of THz pulse generation with energies on the scale of 10 J by using an amplified Ti:sapphire laser with low repetition frequencies.14,15 To make the technique versatile for applications and useful for study of unexplored nonlinear phenomena, a generation setup to obtain optimal THz beam characteristics and a maximized THz peak field is required. A recent detailed analysis of the scheme predicted that the imaging errors in the setup consisting of a grating and lenses can lead to distortion in THz intensity profile after the LiNbO 3 output surface. 16 This distortion could create strong and ambiguous divergence in the THz beam, causing inaccuracy in optimal optis design for THz measurement, thereby limiting its applications.In this paper, we report the generation of single-cycle THz pulses using the tilted-pump-pulse-front scheme with a 1.3 mol % MgO-doped stoichiometric LiNbO 3 ͑LN͒ crystal. In the THz generation setup, the condition that the image of the grating coincides with the tilted-optical-pulse front is fulfilled to obtain optimal THz beam characteristics and pumpto-THz conversion efficiency. The propagation characteristics of the THz beam leaving the output face of the LN crystal were measured by an uncooled microbolometer-array THz camera. The results show that the THz beam had divergence of 52Ϯ 5 mrad in the horizontal direction for 1 THz.The designed focusing geometry for the collimated THz beam enables tight focus onto the electro-optic ͑EO͒ crystal with a spot size ...

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confidence: 98%

Single-cycle terahertz pulses with amplitudes exceeding 1 MV/cm generated by optical rectification in LiNbO3

Hirori

Doi

Blanchard

et al. 2011

Applied Physics Letters

786

501

View full text Add to dashboard Cite

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“…This red-shift is characteristic of the THz generation process 24,26,53,54 , which occurs through difference-frequency mixing among the optical spectral components 34,53,55 and which can be cascaded through multiple difference-frequency steps, leading greater than 100% photon conversion efficiencies.…”

Section: B Thz Pulse Energy and Conversion Efficiencymentioning

confidence: 99%

THz generation using a reflective stair-step echelon

et al. 2016

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We present a novel method for THz generation in lithium niobate using a reflective stair-step echelon structure. The echelon produces a discretely tilted pulse front with less angular dispersion compared to a high groove-density grating. The THz output was characterized using both a 1-lens and 3-lens imaging system to set the tilt angle at room and cryogenic temperatures. Using broadband 800 nm pulses with a pulse energy of 0.95 mJ and a pulse duration of 70 fs (24 nm FWHM bandwidth, 39 fs transform limited width), we produced THz pulses with field strengths as high as 500 kV/cm and pulse energies as high as 3.1 µJ. The highest conversion efficiency we obtained was 0.33%. In addition, we find that the echelon is easily implemented into an experimental setup for quick alignment and optimization.

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“…Optical rectification, on the other hand, has been widely implemented to generate pulses at low THz frequencies [7]. Because the nonlinear process can be cascaded, over 100% of photon conversion efficiency has been demonstrated [8,9]. Of the common nonlinear materials used for OR, ZnTe presents the problem of free carrier absorption, limiting the total efficiency [10].…”

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“…Figure 3 shows the spectral broadening experienced by the IR beam after the THz generation stage. This is a typical signature of highly efficient THz generation, where cascaded OR can greatly surpass the Manley-Rowe limit [17]: an excitation photon emitting one THz photon converts into an optical beam with a small red-shift that can be re-used for THz generation if the phase matching condition is fulfilled [9]. To further enhance the efficiency, we lowered the absorption of lithium niobate at THz frequencies by cooling it to cryogenic temperatures.…”

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High conversion efficiency, high energy terahertz pulses by optical rectification in cryogenically cooled lithium niobate

et al. 2013

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The scope of applications that require intense and ultrafast THz fields has been increasing during the last years. Applications such as terahertz time-domain spectroscopy [1], the study of carrier dynamics in semiconductors [2], electric field gating of interlayer charge transport in superconductors [3], or THz assisted attosecond pulse generation [4] benefit from higher pulse energies than currently available, and so there is keen interest in scaling the peak power of the THz generation schemes. More recently, high peak power THz sources have been proposed for charged particle acceleration, undulation, deflection and spatiotemporal arbitrary manipulation too [5].There are different methods for generating high peak field THz pulses. Among them, difference frequency generation (DFG) and optical rectification (OR) are the most common. Sell et al. demonstrated that it is possible to use DFG between two parametrically amplified pulse trains to generate phase locked terahertz transients with peak electric fields of 10 8 MV/cm and center frequencies continuously tunable from 10 to 72 THz [6]. However, such methods typically exhibit fairly low photon conversion efficiencies due to the Manley-Rowe limit and are also restricted to high THz frequencies approaching the mid-IR spectral region due to limitations imposed by the phase matching condition in the DFG medium, such as GaSe or AgGaS 2 . Optical rectification, on the other hand, has been widely implemented to generate pulses at low THz frequencies [7]. Because the nonlinear process can be cascaded, over 100% of photon conversion efficiency has been demonstrated [8,9]. Of the common nonlinear materials used for OR, ZnTe presents the problem of free carrier absorption, limiting the total efficiency [10]. Lithium niobate presents multiple advantages such as large d eff , high damage threshold, low THz absorption, and large bandgap, but it requires tilted pulse front pumping techniques to achieve

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Enhancement of terahertz wave generation by cascaded χ^(2) processes in LiNbO_3

Cited by 87 publications

References 23 publications

Single-cycle terahertz pulses with amplitudes exceeding 1 MV/cm generated by optical rectification in LiNbO3

Single-cycle terahertz pulses with amplitudes exceeding 1 MV/cm generated by optical rectification in LiNbO3

THz generation using a reflective stair-step echelon

High conversion efficiency, high energy terahertz pulses by optical rectification in cryogenically cooled lithium niobate

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