Theory of thermal self-action in second-harmonic generation in nonlinear crystals

Dmitriev, Valentin G; Konovalov, V A; Shalaev, E A

doi:10.1070/qe1975v005n03abeh010981

Cited by 5 publications

(6 citation statements)

References 1 publication

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“…When we consider the effect of frequency chirp due to the imperfect compression, where the time-bandwidth product is ~0.68 (about twice the diffraction-limited value), the conversion efficiency drops by additional ~5% at an optimal beam waist. A nonideal beam profile at each position along the propagation direction and a temperature gradient [18,19] produced by the high-average-power beam inside the LBO crystal are expected to further reduce the conversion efficiency in the experiment, as discussed in next section. In view of our calculations, 80% of conversion efficiency shown in Ref [9].…”

Section: Shg Using Noncritially Phase-matched Lbo Crystalmentioning

confidence: 99%

130-W picosecond green laser based on a frequency-doubled hybrid cryogenic Yb:YAG amplifier

Hong¹,

Lai²,

Siddiqui³

et al. 2009

Opt. Express

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130-W average-power picosecond green laser pulses at 514.5 nm are generated from a frequency-doubled hybrid cryogenic Yb:YAG laser. A second-harmonic conversion efficiency of 54% is achieved with a 15-mm-long noncritically phase-matched lithium triborate (LBO) crystal from a 240-W 8-ps 78-MHz pulse train at 1029 nm. The high-average-power hybrid laser system consists of a picosecond fiber chirped-pulse amplification seed source and a cryogenically-cooled double-pass Yb:YAG amplifier. The M(2) value of 2.7, measured at 77 W of second-harmonic power, demonstrates a good focusing quality. A thermal analysis shows that the longitudinal temperature gradient can be the main limiting factor in the second-harmonic efficiency. To our best knowledge, this is the highest-average-power green laser source generating picosecond pulses.

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Section: Shg Using Noncritially Phase-matched Lbo Crystalmentioning

confidence: 99%

130-W picosecond green laser based on a frequency-doubled hybrid cryogenic Yb:YAG amplifier

Hong¹,

Lai²,

Siddiqui³

et al. 2009

Opt. Express

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“…The results of other conditions are tabulated in Table 3. Conversion efficiency is higher when input intensity is higher under phase-matching conditions (already known in [2,3]). The absorption coefficient of the second harmonic is about eight times as high as the fundamental in KTP [3], so therefore the absorption ratio increases as efficiency is higher.…”

Section: Analysis Results and Discussionmentioning

confidence: 96%

“…Frequency conversion using nonlinear optical crystals is an indispensable technique for laser precision microfabrications, especially in solid state laser applications. Researches and developments concerning frequency conversion with repetitive irradiation have been mainly conducted experimentally or empirically, and conventional theoretical studies have supposed one pulse-irradiation, although practical frequency conversions are used with repetitive irradiation [1][2][3]. In harmonic generation, phase-matching is essential to obtain maximum conversion efficiency [2].…”

Section: Introductionmentioning

confidence: 99%

“…In this study, we theoretically analyzed second harmonic generation (SHG) to consider the influence of laser absorption with repetitive irradiation. Truncated equations for complex amplitudes used in conventional studies exclude laser absorption [2,3]. We derived truncated equations including laser absorption in the nonlinear optical crystal for SHG and then constructed a coupled analysis model of the propagation of light waves and heat conduction in the crystal.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of Second Harmonic Pulse Distortion Induced by Repetitive Irradiation

Nomura

Ohmura

Miyamoto

2006

MSF

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Shorter pulse duration and higher power lasers have accelerated the development of frequency conversion technique using nonlinear optical crystals for laser precision microfabrications. Previous theoretical studies concerning frequency conversion supposed one-pulse irradiation; accordingly, the influence of the temperature change of crystal induced by laser absorption was not considered, although practical frequency conversions are used with repetitive irradiation. Therefore, researches and developments of harmonic generation with repetitive irradiation have been approached experimentally or empirically. In this study, second harmonic generation considering laser absorption was analyzed theoretically. Output second harmonic pulse shape influenced by repetitive irradiation was evaluated, supposing that the intensity distribution of input pulse was temporal- and spatial-Gaussian. It was quantitatively revealed that a beam profile of output second harmonic pulse, especially generated by high input intensity, is distorted temporally and spatially even during extremely short time-ranges of one pulse. Our analysis suggests the possibility that this pulse distortion influences on processing accuracy.

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“…An experimental measurement of internal temperature is very difficult especially in frequency conversions with focused beam. However most of conventional theoretical studies excluded the input fundamental depletion and effects of laser absorption [1,[5][6][7]. There are several studies considering laser absorption, but they are based on one pulse irradiation [8] or steady state problem on the assumption of low repetition rate [9].…”

Section: Introductionmentioning

confidence: 99%

Theoretical Analysis of Second Harmonic Generation Considering Laser Absorption with Repetitive Irradiation of Focused Beam

Nomura

2006

JLMN

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Employing optical phase-contrast microscopy we study the morphology of ultrashort pulsed laser-induced modifications in bulk fused silica and in other optical transparent materials for different conditions of irradiation. The influence of the input pulse energy, focusing depth, and number of pulses per site is investigated in order to establish optimal irradiation conditions for direct writing of waveguiding elements. The results obtained suggest that an increase of the refractive index is systematically accompanied by a region of lower index of refraction along the optical axis, presumably due to micro-explosion in the high energy-exposed regions, and the locations of this region is material dependent. Nevertheless, the creation of an hypothetical void in the interaction zone does not allow a complete explanation of the modifications observed and other mechanisms have to be invoked to explain the presence of regions with higher index of refraction. Different interaction regimes with respect to the input energy and to the number of shots per site can be established from these observations, emphasizing the role of nonlinear pulse propagation and plasma generation. To complement the experimental observations we simulate the propagation of an ultrashort laser pulse in bulk silica using the non-linear Schrödinger equation and determine the distribution of energy along the propagation axis. The results are in good agreement with the experimental observations and provides insights into the mechanisms controlling the interaction between ultrashort laser pulses and transparent materials.

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Theory of thermal self-action in second-harmonic generation in nonlinear crystals

Cited by 5 publications

References 1 publication

130-W picosecond green laser based on a frequency-doubled hybrid cryogenic Yb:YAG amplifier

130-W picosecond green laser based on a frequency-doubled hybrid cryogenic Yb:YAG amplifier

Analysis of Second Harmonic Pulse Distortion Induced by Repetitive Irradiation

Theoretical Analysis of Second Harmonic Generation Considering Laser Absorption with Repetitive Irradiation of Focused Beam

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