Laser Systems

ATF is the world's only user facility offering access to a terawatt-class, picosecond long-wave infrared (LWIR) laser system. The facility also provides a terawatt-class near-infrared (NIR) laser. Both lasers are synchronized to the electron beam with sub-100 fs precision, enabling all three beams to be brought together at a single interaction point.

LWIR Laser

The ATF's ultrafast 9.2 µm LWIR laser system is based on the facility's high-pressure, mixed-isotope CO₂ gas amplifier technology [1]. The seed pulse is generated by a solid-state wavelength-conversion chain driven by a Ti:Sapphire laser.

Schematic of the ATF’s 9.2-µm laser system.

The ATF laser is the first to implement chirped-pulse amplification (CPA) in gas amplifiers [2]. Peak powers of 5 TW with 2 ps pulse duration have been demonstrated at the output of the CPA compressor [3]. For user experiments, the system typically delivers 2–3 TW pulses at a repetition interval of approximately 90 s.

Ongoing research and development has established a clear path toward shorter, more powerful pulses. The next performance milestone is 15 TW peak power with 500 fs pulse duration, followed by a long-term goal of 25 TW with 100 fs (approximately three optical cycles) pulse duration [4].

Typical operating parameters for the ATF LWIR laser system.

Parameter	Value	Notes
Central wavelength	9.24 µm
FWHM bandwidth	0.10 µm
FWHM pulse duration	2.0 ps	70 ps with compressor bypassed
Pulse energy	≤7 J	≤10 J with compressor bypassed
Peak power	≤3 TW
Pulse repetition interval	≥90 s

The LWIR laser system produces linearly polarized pulses, with the polarization plane rotatable to an arbitrary angle. Circular polarization can be generated at reduced pulse energy (typically <0.5 J).

For experimental setup and alignment, the system can provide millijoule-level pulses at a repetition rate of 1.5 Hz with the final amplifier unpumped.

NIR Lasers

The ATF offers a significant range of NIR laser capabilities for users as well. The facility's Nd:YAG laser that drives the ATF's RF photocathode gun can also provide beams for experiments. This includes optical pulse trains that are temporally matched to the electron bunch trains from the linac. These trains can be up to 100 pulses in length with a period of 40.8 MHz, or ~2.5 microseconds total. A Ti:Sapphire experimental system compliments the LWIR capabilities of the facility, and significantly expands the types of experiments that can be carried out because of the short pulse duration and wavelength. These beams are utilized as both drive beams for experiments and as diagnostics.

Typical operating parameters for the ATF Ti:Sapphire laser system.

Parameter	Value	Notes
Central wavelength	800 nm
FWHM bandwidth	13 nm
FWHM pulse duration	<85 fs	>50 ps with compressor bypassed
Pulse energy	100 mJ	200 mJ with compressor bypassed

Typical operating parameters for the ATF Nd:YAG laser system.

Parameter	Fundamental	Frequency doubled	Notes
Wavelength	1064 nm	532 nm
FWHM pulse duration	14 ps	10 ps
Pulse energy	<20 mJ	0.5 mJ	<100 mJ @ BL1 in EH

Diagnostics

ATF provides a comprehensive suite of diagnostics for characterizing both the near-infrared (NIR) and long-wave infrared (LWIR) laser systems. Available diagnostics include:

• Energy and power measurements: Power and energy meters, including systems capable of measuring pulse energies up to 30 J.
• Pulse duration diagnostics:
• Single-shot autocorrelators with <50 fs resolution (LWIR and NIR)
• Scanning autocorrelators with <40 fs resolution (NIR)
• Frequency-resolved optical gating (FROG) system at 800 nm with <100 fs resolution
• Hamamatsu C10910 universal streak camera with ~1 ps temporal resolution (UV to NIR). An in-house-developed wavelength-conversion setup extends its capability to characterize LWIR pulses.
• High-speed photodetectors for NIR measurements up to 50 GHz
• Nanosecond IR photodetectors for LWIR diagnostics
• Real-time oscilloscopes up to 5 GHz
• Equivalent-time (sampling) oscilloscopes up to 50 GHz
• Spectral diagnostics:
• Custom-built LWIR spectrometers
• 1/4-meter imaging spectrometer
• Fiber-coupled spectrometers covering the visible to 1.4 µm spectral range
• Beam diagnostics:
• Pyroelectric camera beam-profile monitors for the LWIR laser
• CCD beam-profile cameras for the NIR laser
• Wavefront sensor (NIR)
• Beam-focus imaging systems at the experimental interaction point
• Handheld IR viewers and laser viewing cards

Several diagnostics provide real-time online data that may be incorporated into user data sets for post-processing, e.g. normalizing measurements to laser pulse energy.

References

[1] M. N. Polyanskiy, I. V. Pogorelsky, and V. Yakimenko, "Picosecond pulse amplification in isotopic CO₂ active medium," Optics Express 19, 7717–7725 (2011). https://doi.org/10.1364/OE.19.007717

[2] M. N. Polyanskiy, M. Babzien, and I. V. Pogorelsky, "Chirped-pulse amplification in a CO₂ laser," Optica2, 675–681 (2015). https://doi.org/10.1364/OPTICA.2.000675

[3] M. N. Polyanskiy, I. V. Pogorelsky, M. Babzien, and M. A. Palmer, "Demonstration of a 2 ps, 5 TW peak power, long-wave infrared laser based on chirped-pulse amplification with mixed-isotope CO2 amplifiers," OSA Continuum3, 459–472 (2020). https://doi.org/10.1364/OSAC.381467

[4] Report of the Basic Research Needs Workshop on Laser Technology. U.S. Department of Energy Office of Science and National Science Foundation, January 2024. Available at: https://science.osti.gov/-/media/ardap/pdf/2024/Laser-Technology-Workshop-Report_20240105_final.pdf