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Description
Strong field science rapidly grew in the 1990s with the emergence of Ti:Sapphire based chirped pulse amplification (CPA) systems operating at 0.8 µm wavelength. Although many strong-field phenomena benefit from longer laser wavelengths [1, 2], to date this field has been largely restricted to near infrared range of 0.8 to 1 µm. The Fe:ZnSe-based CPA offers an efficient approach for reaching high-peak-power at 4 μm [3]. Our group established a Fe:ZnSe 12-pass CPA laser pumped by two 34-mJ, 120-μs Er:YAG lasers. We demonstrated 250-fs, 4.95-mJ pulses at a center wavelength of 4.07 μm [4]. To increase the output peak power of this system, we are establishing a Fe:ZnSe amplifier pumped by a high-energy laser diodes pumped Er:YAG laser. Here we report the measurements of the time-resolved small signal gain (SSG) of Fe:ZnSe crystals, with a goal of terawatt (TW) mid-infrared CPA.
The schematic of the measurement setup is shown in Fig.1. The updated high-power Fe:ZnSe amplifier is pumped by a diode-pumped Er:YAG laser. We used two 8×8×10 mm3 Fe:ZnSe crystals with the doping concentration of 5ⅹ1018 cm-3. The crystals were mounted in a vacuum chamber, which were cooled to 42 - 90 K to increase the upper-level lifetime and suppress thermal lensing.
The single-pass small signal was measured by using a 4-μm CW laser diode. The results are shown in Fig.2. The time-resolved gain was measured at different pump energies. Fig.2(a) shows the gain at approximately 70-mJ pump energy. The measurement shows a gain of over 23. When increasing the pump energy to 280 mJ, the gain increases to ~150, as shown in Fig.2(b). To the best of our knowledge, this is the highest gain ever reported for an Fe:ZnSe amplifier.
In summary, we obtained a small signal gain of 150 at 280-mJ pump energy when the Fe:ZnSe was cooled to 42 K. We are currently developing a multi-stage, multi-pass Fe:ZnSe CPA laser. The first stage amplifier is expected to deliver >30-mJ pulses at 100 Hz, which will be further amplified to TW for attosecond science and other strong field physics experiments.
| Keyword-1 | Fe:ZnSe Amplifier |
|---|---|
| Keyword-2 | Mid-infrared laser |