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Pulse length of ultracold electron bunches extracted from a laser cooled gas

机译:从激光冷却气体中提取的超冷电子束的脉冲长度

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摘要

We present measurements of the pulse length of ultracold electron bunches generated by near-threshold two-photon photoionization of a laser-cooled gas. The pulse length has been measured using a resonant 3 GHz deflecting cavity in TM110 mode. We have measured the pulse length in three ionization regimes. The first is direct two-photon photoionization using only a 480 nm femtosecond laser pulse, which results in short (∼15 ps) but hot (∼104 K) electron bunches. The second regime is just-above-threshold femtosecond photoionization employing the combination of a continuous-wave 780 nm excitation laser and a tunable 480 nm femtosecond ionization laser which results in both ultracold (∼10 K) and ultrafast (∼25 ps) electron bunches. These pulses typically contain ∼103 electrons and have a root-mean-square normalized transverse beam emittance of 1.5 ± 0.1 nm rad. The measured pulse lengths are limited by the energy spread associated with the longitudinal size of the ionization volume, as expected. The third regime is just-below-threshold ionization which produces Rydberg states which slowly ionize on microsecond time scales.
机译:我们介绍了由激光冷却气体的近阈值双光子光电离所产生的超冷电子束的脉冲长度的测量结果。脉冲长度是使用TM110模式的谐振3 GHz偏转腔测量的。我们已经在三种电离方式下测量了脉冲长度。第一个是仅使用480 nm飞秒激光脉冲进行的直接双光子光电离,这会导致短(约15 ps)但很热的电子束(约10 4 K)。第二种方法是高于阈值的飞秒光电离,结合了连续波780 nm激发激光和可调谐480 nm飞秒电离激光,产生了超冷(〜10 K)和超快(〜25 ps)电子束。这些脉冲通常包含约10 3 个电子,并且具有1.5±0.1 nm rad的均方根归一化横向光束发射率。如所期望的,所测量的脉冲长度受到与电离体积的纵向尺寸相关的能量散布的限制。第三种机制是低于阈值电离的电离,它会产生Rydberg态,并在微秒的时间尺度上缓慢电离。

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