一、利用EPOCH研究激光在真空中的傳輸過(guò)程：
?激光波長(zhǎng)1.06um，脈沖寬度 duration = 50 * femto，計(jì)算100fs。
? duration_w = duration / (2.0 * sqrt(loge(2.0))
begin:laser
? boundary = x_min
? intensity_w_cm2 = 1.0e15
? lambda = lambda0 * cos(theta)
? phase = 0? # -2.0 * pi * y * tan(theta) / lambda0
? #pol_angle = pi / 2.0
? profile = gauss(y,0*micron,4*micron)
? t_profile = gauss(time, duration, duration_w)
end:laser
t_profile 設(shè)定高斯分布，初始設(shè)置使得在15um處激光強(qiáng)度達(dá)到最大值。也就是說(shuō)t=15um/c=50fs。計(jì)算時(shí)間為100fs，也就是激光在真空傳輸100fs的時(shí)間，即激光已經(jīng)傳輸?shù)?00fs*c=30um處。這個(gè)點(diǎn)激光在15um處達(dá)到最大。測(cè)試如下：
同理，如果按照激光周期設(shè)置，效果一樣。比如希望激光在達(dá)到15um處的時(shí)候達(dá)到最大，計(jì)算得到此時(shí)的時(shí)間=14.15*laser_cycle(激光周期)。測(cè)試如下：
二、設(shè)置圓偏振光：
begin:laser
? boundary = x_min
? profile = gauss(y, 0, sigma_w0)?? ?
? t_profile = gauss(time, 2*sigma_t , sigma_t) ?? ??? ?
? phase = 0
? pol_angle = 0?? ??? ?# p-pol = 0.0?? ?s-pol = pi/2?? ?
end:laser
begin:laser
? boundary = x_min
? profile = gauss(y, 0, sigma_w0)?? ?
? t_profile = gauss(time, 2*sigma_t , sigma_t) ?? ??? ?
? phase = pi/2.0
? pol_angle = pi/2.0?? ?# p-pol = 0.0?? ?s-pol = pi/2?? ?
end:laser
三、Beam waist is defined as the 1/e spatial extent of the electric field of the pulse. So if you take an intensity FWHM width, you need to divide it by 2*sqrt(ln(2)) to get the intensity 1/e width. You then need to multiply by another sqrt(2) to get the 1/e2 width of the intensity profile, which is equal to the 1/e electric field width.
