Self-mode locking of a diode-pumped Nd:YLF laser

Generation of terahertz optical beating from a simultaneously self-mode-locked Nd:YAG laser at 1064 and 1123 nm

The reflectivity of the output coupler is designed to achieve the synchronously self-mode-locked operation at 1064 and 1123 nm in a diode-end-pumped Nd:YAG laser. Numerical analyses are performed to confirm that the designed output coupler can lead the emission lines to be predominant at 1064 and 1123 nm. Moreover, the crossover of the threshold pump powers for the 1064 and 1123 nm emission lines can be exploited to obtain the single central wavelength of 1064 nm or the single central wavelength of 1123 nm or, simultaneously, dual-central-wavelength self-mode-locked operation by finely adjusting the cavity alignment. For the dual-central-wavelength mode-locked emissions, the pulse repetition rate and the pulse duration are 4.5 GHz and 50.8 ps, respectively. The maximum output power can be up to 2.47 W at a pump power of 7.5 W. The synchronization of the 1064 and 1123 nm mode-locked pulses generates the optical beating pulse trains with repetition rates up to 14.7 THz.

Pr3+:YLF mode-locked laser at 640 nm directly pumped by InGaN-diode lasers

We attain stable mode-locking of an InGaN laser-diode-pumped Pr³⁺:YLF laser with a pump power of 2.8 W using a semiconductor saturable absorption mirror. A maximum averaged output power of 65 mW was obtained with a 45-ps pulse width at a pulse repetition rate of 108 MHz. We also attempted Kerr-lens mode-locking by employing an SF57 glass in a cavity as a Kerr medium.

Mode locking with enhanced nonlinearity--a detailed study

We explore mode locked operation of a Ti:Sapphire laser with enhanced Kerr nonlinearity, where the threshold for pulsed operation can be continuously tuned down to the threshold for continuous-wave (CW) operation, and even below it. At the point of equality, even though a CW solution does not exist, pulsed oscillation can be realized directly from zero CW oscillation. We experimentally investigate the evolution of the mode locking mechanism towards this point and beyond it, and provide a qualitative theoretical model to explain the results.

Observation of strong cascaded Kerr-lens dynamics in an optimally-coupled cw intracavity frequency-doubled Nd:YLF ring laser

Self-starting self-pulsing dynamics at the cavity free-spectral-range frequency were observed in intracavity second-harmonic generation of a diode end-pumped Nd:YLF ring laser containing a periodically-poled KTiOPO(4) (ppKTP) nonlinear crystal. Although the unidirectional laser was designed for continuous-wave (cw) single-frequency operation, with a resonator set at the middle of its stability range, partial Kerr-lens mode-locking (KLM) arose spontaneously once the ppKTP was inserted. This ultrafast dynamics along with a strong spectral gain broadening, not observed with any birefringent nonlinear doubler, is associated to the finite bandwidth of the quasi-phase-matched crystal with respect to the laser gain bandwidth, leading to giant cascaded Kerr-lensing effects when the ppKTP temperature is detuned from perfect quasi-phase-matching either in the self-focusing or defocusing sides. While under partial KLM operation the laser delivered only approximately 0.14W of broadband red output power, single-frequency operation could be only achieved by using an intracavity etalon with a suitable partial reflectivity (R>or=25%), leading to an optimally (approximately100% efficiency) out-coupled 1.4 W red power at 660.5 nm, as much as the fundamental 1321 nm power that could be extracted from the unidirectional laser using an optimal T = 2% output coupler.

Compact efficient multi-GHz Kerr-lens mode-locked diode-pumped Nd:YVO4 laser

We demonstrate the compact efficient multi-GHz Kerr-lens mode locking in a diode-pumped Nd:YVO(4) laser with a simple linear cavity without the need of any additional components. Experimental results reveal that the laser system can be characterized in stable single-pulse and multiple-pulse mode-locked operations. With a pump power of 2.5 W, the compact laser cavity produces average output powers greater than 0.8 W with a pulse width less than 10 ps in the range of 2-6 GHz.

Sensitivity of a three-mirror cavity to thermal and nonlinear lensing: Gaussian-beam analysis

We consider a compact three-mirror cavity consisting of a flat output coupler, a curved folding mirror, and an active medium with one facet cut at the Brewster angle and the other facet coated for unit reflectivity. We examine the sensitivity to thermal lensing and to self-focusing in the active medium of the Gaussian beam that is circulating in that cavity. We use a simple thin-lens model; the astigmatism of the beam that is circulating in the cavity and the nonlinear coupling between the field distributions along the two orthogonal axes are taken into account. We find configurations in which beam ellipticity is compensated for at either end of the cavity in the presence of thermal lensing. We have derived an analytical criterion that predicts the sensitivity of the beam size to nonlinear lensing. The ability of the cavity to favor self-mode locking is found to be sensitive to the strength of thermal lensing. In the absence of thermal lensing, cavities operated as telescopic systems (C = 0) or self-imaging systems (B = 0) are most appropriate for achieving self-mode locking, with nonlinear mode selection accomplished through saturation of the spatially varying laser gain. We identify conditions for which self-mode locking can be produced by variable-reflectivity output couplers with either maximum or minimum reflectivity at the center of the coupler. We use our model to estimate the nonlinear gain produced in laser cavities equipped with such output couplers. We identify a cavity configuration for which nonlinear lensing can simultaneously produce mode locking and correction of beam ellipticity at the output coupler.

Cavity-dumped femtosecond Kerr-lens mode locking in a chromium-doped forsterite laser

We report the operation of a cavity-dumped self-mode-locked chromium-doped forsterite laser with pulse energies exceeding 30 nJ and pulse durations as short as 54 fs (FWHM) at 1260 nm. By frequency doubling in a beta-barium borate crystal, pulse energies as high as 3 nJ and pulse durations as short as 49 fs (FWHM) at 630 nm were generated. The high stability and ultrashort pulse widths with a variable repetition rate in both the infrared (1260 nm) and the red (630 nm) make this system an attractive light source for ultrafast spectroscopy.

Efficient continuous-wave TEM(00) and femtosecond Kerr-lens mode-locked Cr:LiSrGaF laser

Efficient high-power (900-mW) TEM(00) cw operation of a Cr:LiSrGaF laser pumped by a Kr(+) laser is demonstrated. The results of laser and spectroscopic analysis, including upconversion and excited-state absorption, are presented and used for the optimization of this laser. Kr(+)-laser-pumped mode-locked femtosecond operation (64 fs) was performed. Use of a modified resonator, which can decrease the threshold pump and intracavity power for Kerr-lens mode locking and increase the mode-locked output power (300 mW), is suggested. The inf luence of crystal axis misalignment on the tuning and mode-locking characteristics of the laser is studied.

Self-starting self-mode-locked femtosecond diode-pumped Cr:LiSAF laser

We describe a diode-pumped Kerr-lens mode-locked Cr(3+):LiSrAlF(6) laser that produces 50 mW of 70-fs pulses in the 820-890-nm range when pumped by two red diodes of 400 mW each. By using a lower-transmission output coupler we have demonstrated for the first time to our knowledge a self-starting regime with an output power of 10 mW and 55-fs pulses.

Diode-pumped Nd:YLF all-in-one laser

A high-power longitudinally end-diode-pumped Nd:YLF all-in-one laser has been constructed and tested. The compact single-cavity laser generates pulses with durations of 28 ps. Pulse energies of ~120 or -500 microJ are measured at a 1-kHz repetition rate when the all-in-one laser is pumped with a 3- or 15-W diode laser, respectively. Controlled prelasing is utilized to prevent the buildup of large-amplitude relaxation oscillations and to minimize the prelasing leakage. Pulse shaping in the all-in-one laser is analyzed in terms of the Kuizenga-Siegman theory.

Self-starting mode locking of a cw Nd:YAG laser using cascaded second-order nonlinearities

The nonlinear mode variations induced by the equivalent third-order susceptibility resulting from cascaded secondorder nonlinearities in an intracavity lithium triborate crystal are exploited for mode locking of a cw Nd:YAG laser. The loss modulations are provided by a slit, as in the Kerr-lens mode-locking scheme. The mode-locking process is self-starting and produces nearly transform-limited pulses of 14-ps duration with 0.5-W average power.

High-power longitudinally end-diode-pumped Nd:YLF regenerative amplifier

We describe a high-power compact diode-pumped Nd:YLF regenerative amplifier. The pumping source is a 15-W diode-laser array that is focused into the laser crystal with a longitudinal end-pumping arrangement based on an array of cylindrical microlenses. Seeded with 15-ps pulses from a diode-pumped and mode-locked Nd:YLF oscillator, the regenerative amplifier produces pulses of 0.5-mJ energy at a 1-kHz repetition rate. A pulse energy as high as 0.75 mJ is achieved at a 500-Hz repetition rate and below.

All-solid-state self-mode locking of a Nd:YLF laser

An all-solid-state, Kerr-lens mode-locked Nd:YLF laser is reported that uses a simple X-fold cavity with separate gain and nonlinear media. Self-starting pulses of 3 ps are reported at 1.047 microm with significant enhancements in stability and starting behavior over previous Kerr-lens mode-locked Nd:YLF lasers. The benefits of this X-fold cavity design for general passive mode locking of laser-diode-pumped solid-state lasers are also addressed.

Frequency-modulation mode-locking performance for four Nd(3+)-doped laser crystals

To determine an optimum host for simultaneous short-pulse-width and large-slope-efficiency generation, the performance of Nd:YAG, Nd:YLF, Nd:YVO(4), and Nd(3+):Sr(5)(VO(4))(3)F [Nd:strontium fluorovanadate (S-VAP)] was characterized under a variety of end-pumped and frequency-modulation mode-locking conditions. The slope efficiency, threshold pump power, and pulse width were recorded for each laser and compared with theory. A figure of merit was defined, yielding Nd:YLF and Nd:YVO(4) as the experimentally determined crystals of choice.

Self-mode-locked NaCl:OH(-) color-center laser

We have demonstrated self-mode locking of an NaCl:OH,(-) color-center laser by exploiting the Kerr effect in a rod of high-nonlinearity glass placed within the laser cavity. The mode-locking process was initiated by a regenerative acousto-optic modulation, and sub-100-fs pulses were produced at wavelengths of ~1575 nm.

Generation of pulses as short as 93 fs from self-starting femtosecond Cr:LiSrAlF(6) lasers by exploiting multiple-quantum-well absorbers

A Cr:LiSrAIF(6) laser has been mode locked by using a multiple-quantum-well (MQW) absorber. With the MQW absorber inside the laser cavity, Kerr lens mode locking is initiated, yielding transform-limited pulses as short as 93 fs. Pulses of 500-fs duration have also been produced by using resonant passive mode locking with the MQW absorber in an external cavity.

Kerr lens effects in a ring resonator with an aperture:mode locking and unidirectional operation

A ring resonator containing a Kerr lens and a Gaussian slit is analyzed. From the point of view of Kerr lens mode locking, it is shown that a self-defocusing nonlinear element is as effective as a self-focusing one and that the positioning of the Kerr element introduces trade-offs between self-starting and operational stabilization. The nonlinearity can lead to unidirectional lasing.

Diode-pumped Nd:YLF regenerative amplifier

A diode-pumped Nd:YLF regenerative amplifier operating at 1047 nm produces 88-microJ, 11-ps pulses at a 1-kHz repetition frequency. Switching of the 250-MHz seed pulses with a Pockels cell in the half-wave configuration is achieved with a contrast ratio of 20:1. After 50 round trips, the amplified pulse experiences an overall energy gain of 73 dB when the amplifier is seeded with 4-pJ pulses (1-mW average seed power). At 1 kHz, doubling and quadrupling yields 46 microJ/pulse at 524 nm and 8.1 microJ/pulse at 262 nm, with corresponding conversion efficiencies of 52% and 23%. At 3.5 kHz, the amplifier generated 97 mW of power at 524 nm and 15.8 mW of power at 262 nm.

Kerr lens mode locking

Self-focusing in conjunction with an intracavity aperture creates a power-dependent amplitude modulation in laser oscillators, which allows passive mode locking. A simple analytical formalism yields closed-form expressions for the depth of passive amplitude modulation introduced by either the spatial gain profile or a hard aperture inserted in the resonator. Design issues for this mode-locking technique are discussed.