PurposeTo examine the associations of near work related parameters with spherical equivalent refraction and axial length in Chinese children.MethodsA total of 1770 grade 7 students with mean age of 12.7 years were examined with cycloplegic autorefraction and axial length. Questions were asked regarding time spent in near work and outdoors per day, and near work related parameters.ResultsMultivariate models revealed the following associations with greater odds of myopia: continuous reading (> 45min), odds ratio [OR], 1.4; 95% confidence interval [CI], 1.1-1.8; close television viewing distance (≤ 3m), OR, 1.7; 95% CI, 1.2-2.3; head tilt when writing, OR, 1.3; 95% CI, 1.1-1.7, and desk lighting using fluorescent vs. incandescent lamp, OR, 1.5; 95% CI, 1.2-2.0. These factors, together with close reading distance and close nib-to-fingertip distance were significantly associated with greater myopia (P<0.01). Among near work activities, only reading more books for pleasure was significantly associated with greater myopia (P=0.03). Television viewing distance (≤ 3 m), fluorescent desk light, close reading distance (≤20 cm) and close nib-to-fingertip distance (≤ 2 cm) were significantly associated with longer axial length (P<0.01). Reading distance, desk light, and reading books for pleasure had significant interaction effects with parental myopia.ConclusionsContinuous reading, close distances of reading, television viewing and nib-to-fingertip, head tilt when writing, reading more books for pleasure and use of fluorescent desk light were significantly associated with myopia in 12-year-old Chinese children, which indicates that visual behaviors and environments may be important factors mediating the effects of near work on myopia.

The 14-year-old group had larger parameter dimensions than the 7-year-old group except for corneal radius of curvature (unchanged) and lens thickness and corneal diameter (both smaller). Boys had large parameter dimensions than girls except for lens thickness (smaller). Axial length, corneal radius of curvature, and lens thickness were the most important determinants of refraction.

We experimentally investigate the limits to 800 nm-to-terahertz (THz) energy conversion in lithium niobate at room temperature driven by amplified Ti:Sapphire laser pulses with tilted-pulse-front. The influence of the pump central wavelength, pulse duration, and fluence on THz generation is studied. We achieved a high peak efficiency of 0.12% using transform limited 150 fs pulses and observed saturation of the optical to THz conversion efficiency at a fluence of 15 mJ/cm 2 . We experimentally identify two main limitations for the scaling of optical-to-THz conversion efficiencies: (i) the large spectral broadening of the optical pump spectrum in combination with large angular dispersion of the tilted-pulse-front and (ii) free-carrier absorption of THz radiation due to multi-photon absorption of the 800 nm radiation. Strong-field terahertz (THz) sources hold promise for enabling myriads of novel applications. They possess intense electric and magnetic fields at frequencies which are particularly amenable to studies of condensed matter dynamics [1][2][3], manipulation of molecules [4], highharmonic generation (HHG) [5], and compact chargedparticle acceleration [6][7], among others. Therefore, there is a great need for the development of robust and efficient strong-field THz sources.These sources are predominantly accelerator-based facilities (delivering up to 100 µJ THz energy) [8,9] or ultrafast laser-based table-top systems [10]. Laboratory scale systems are of particular interest due to accessibility and relatively low cost. In this category, laser-induced air/gas plasmas (delivering up to 5 µJ THz energy) [11] and optical rectification (OR) of infrared (IR) pulses in nonlinear optical crystals (delivering up to 0.4 mJ THz energy) [12] have emerged as the most common methods of all THz generation modalities. The highest optical-toTHz conversion efficiencies (henceforth referred to as conversion efficiency) in excess of 1% at room temperature have been achieved by OR employing angularly dispersed femtosecond IR pump pulses in lithium niobate [13,14]. As a result, these systems are especially relevant to generating mJ-level THz pulses [12]. In this approach, angular dispersion is introduced to compensate for the large difference in refractive indices between IR and THz frequencies by forming a tilted-pulse-front. The generated THz then propagates perpendicular to this tilted-pulsefront and phase matching is achieved in a non-collinear configuration. OR systems based on lithium niobate are powered predominantly by sources in the 1 µm and 800 nm wavelength regions. While the former yields much higher conversion efficiencies, today, 800 nm sources based on Ti:Sapphire systems prevail in ultrafast laser technology as the most accessible and widely employed sources. Consequently, exploring the limits to achievable conversion efficiency is a great value in the pursuit of accessible high-energy THz sources.In this paper we extensively investigate the limits of conversion efficiency with 800 nm systems through a systemati...