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Kerr-lens mode locking (KLM) is the engine of ultrafast laser sources. A major research effort in our group is to explore the physics of mode locking. We manipulate and examine the Kerr-lens mechanism in various aspects with the aim to develop sources of ultrashort pulses and optical frequency combs with desirable optical properties that are otherwise unattainable: Specifically, we demonstrated robust and flexible control of the oscillation spectrum by shaping the gain of a KLM Ti:Sapphire laser, which steers the spectral mode-competition in a unique manner. By enhancing the nonlinearity in the laser cavity we could lower the mode-locking threshold drastically, even below the CW threshold, and explored its relevance for mode-locking with low intracavity pulse energy and high repetition rate. Recently, we examined the dynamical evolution of KLM with a complete numerical simulation of the laser operation., which led to a direct observation (in both simulation and experiment) of the nonlinear saturable loss mechanism that is responsible for the pulse formation [2] and we predicted and demonstrated a new effect in KLM, where the symmetry between the forward and backwards directions in a linear cavity is broken by the dual interaction with the Kerr-lens[1].

Mode locking of semiconductor lasers with high pulse energy is a major applicative effort in my group. Relying on our expertise in laser physics and mode-locking we develop external cavity configurations, where short pulses of picosecond duration (6-100ps), record-high pulse energies (nano-Joule scale), and repetition rate in the range of 60-700MHz are generated from standard broad-area edge-emitter gain-chips that are driven by pulses of electrical current. This forms a breakthrough in mode-locking of semiconductor lasers, where pulse energies so far were in the few pJ range (or less) and multi-GHz repetition rates, limited primarily by the short excited-state lifetime in the semiconductor medium. A broad-area gain chip enables high pumping currents (>10A) and very high optical power, while the design of the external cavity enforces lasing with a single spatial mode and high-power efficiency (>75%, 2 watts,  demonstrated in CW) with broad-area chips that are normally highly multimode. To mode-lock the laser we combine active and passive methods: Active mode-locking is invoked by pumping the chip with current pulses, that are synchronized with the repetition rate of the cavity (60-70MHz) and whose duration (few ns) matches the lifetime of the excited state in the semiconductor medium [in preparation]. This active gain switching generates optical pulses of 60-100ps duration with an energy of ~0.5nJ. For shorter pulses of 6-10ps duration, we employ passive mode-locking with an integral saturable absorber section on the gain chip that can be precisely reverse-biased for optimal pulse generation.

Kerr-lens mode-locking (KLM) dynamics: Research

relevant publications:

  1. Idan Parshani, Leon Bello, Mallachi Meller and Avi Pe’er, “Kerr-Lens Mode-Locking: Numerical Simulation of the Spatio-Temporal Dynamics on All Time Scales”, Applied Sciences 12, 10354 (2022)

  2. Idan Parshani, Leon Bello, Mallachi Meller and Avi Pe’er, “Passive symmetry breaking of the space–time propagation in cavity dissipative solitons”, Scientific Reports 12, 14874 (2022)

  3. Idan Parshani, Leon Bello, Mallachi Meller and Avi Pe’er, “Diffractive saturable loss mechanism in Kerr-lens mode-locked lasers: direct observation and simulation”, Optics Letters 46, 1530-1533 (2021)

  4. Shai Yefet, Valery Jouravsky and Avi Pe'er, "Kerr-lens Mode Locking Without Nonlinear Astigmatism",
    J. Opt. Soc. Am. B 30, 549–551 (2013)

  5. Mallachi Meller, Shai Yefet and Avi Pe’er, "Mode-Locking With Ultra-Low Intra-Cavity Pulse Intensity Using Enhanced Kerr Nonlinearity",  IEEE J. Quantum Electron. 53, 1300105 (2017)

  6. Tutorial: Yaakov Shaked, Shai Yefet and Avi Pe'er, "Dispersion Compensation using a Prism-pair", arXiv:1411.0232 [physics.optics] (2014)

  7. Review article: Shai Yefet and Avi Pe'er, "A Review of Cavity Design for Kerr Lens Mode-Locked Solid-State Lasers", Appl. Sci. 3, 694-724 (2013)

  8. Shai Yefet, Na’aman Amer, and Avi Pe’er, "Intra-cavity gain shaping of mode-locked Ti:Sapphire laser oscillations", Opt. Express 20, 9991-9998 (2012)

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