Abstract
We studied the hard X-ray emission and the Kα X-ray conversion efficiency (η K ) produced by 70 fs, 400 nm high-contrast femtosecond laser pulse focused on Cu solid target. At an intensity I = 2 × 1018 W · cm−2, the Cu η K can reach 1 × 10−4. Compared with the Cu η K obtained by using a 800-nm low-contrast laser pulse, the second harmonic exhibits a higher X-ray flux by a factor of 2. We show that the use of high-contrast laser pulses may be an effective method to optimize the Kα X-ray emission via the vacuum heating mechanism. In addition, the laser focusing was varied widely to give a range of intensities from 1015–1018 W · cm−2 by target offset from best laser focus. Two individual emission peaks are obtained, one is at best focal spot and the other is at larger target offset corresponding to ∼1015 W · cm−2. Each X-ray emission peak is corresponding to different energy absorption mechanism.
Published Version
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