Using the latter two techniques, pulses of less than 100 fs duration can be readily obtained. Passive modelocking using saturable absorbers an intracavity saturable absorber is able to fix phase of cavity modes variations slow saturable absorber fast saturable absorber kerr lens effect. The laser used a slightly modified standard delta cavity. Onedimensional computer simulations are sufficient to explain. Kerrlens modelocking klm is a method of modelocking lasers via the nonlinear optical kerr effect. This has led to a number of modelocking techniques to obtain such pulses, for example acoustooptic, injection, synchronouspump, collidingpulse modelocking, and kerr lens modelocking. Its strength lies in the very fast response and the fact that no special saturable absorber medium is required. On the contrary, kerrlens modelocking is known to support much shorter pulse durations 23, even beyond the emission bandwidthlimit of the laser gain medium 43,44. A prominent mechanism is the optical kerr effect, which can be viewed as an intensitydependent change of refractive index.
Without any gvd compensation, the single pass gvd for the 9 mm ti. Kerr lens mode locking has enabled the generation of the shortest pulses with durations down to. Yag lasers 2, but kerrlens modelocking is not performed for other ybdoped materials at this moment. As the kerrlens induced in the nonlinear medium strongly depends on the resonator internal power, we have measured the output power in modelocked operation as a function of output coupling see fig. We demonstrate a kerrlens mode locked folded cavity using a planar nonbrewster ti. The general principle behind kerr lens mode locking is sketched in fig. Ylf laser, initiated by means of a liquid saturable absorber. It is known that kerrlens modelocking technique based on the nonlinear refractive index n2 of the laser medium itself is a manner for femtosecond laser pulse generation. Average output power of up to 1 w is demonstrated in a kerrlens mode locked yb.
Frequencydependent mode size in broadband kerrlens mode locking. The total anomalous group delay dispersion gdd per round trip is. Files are available under licenses specified on their description page. The article on passive mode locking explains how a saturable absorber leads to mode locking. A kerrlens modelocked laser has been designed with thinrod yb. In this paper we want to present a new approach for the generation of subps parametric pulses starting with pump pulses of a few ps and introducing kerr lens mode locking 3 as a additional shortening mechanism besides temporal gain. Frequencydependent mode size in broadband kerrlens mode. The mechanism for selfstarting operation of kerrlens modelocking laser is studied. It is developed with a view to modeling kerr lens modelocking, but promises much wider applicability. This has led to a number of modelocking techniques to obtain such pulses, for example acoustooptic, injection, synchronouspump, collidingpulse modelocking, and kerrlens modelocking. Cagdalo 4 oscillator optically pumped by a diffraction limited fiber laser. Modelocked highpower operation has so far only been shown for sesam 2,15, nonlinear polarization rotation 16, or kerrlens mode. The basis of the technique is to induce a fixedphase relationship. Our research is development of highaverage power kerrlens modelocked yb.
A high spatial and spectral quality is achieved, close to the diffraction and fourier transform limitations. Rp photonics encyclopedia kerr lens mode locking, hard. Analytical design of symmetrical kerrlens modelocking laser cavities. All structured data from the file and property namespaces is available under the creative commons cc0 license. Examination of the output beam size from a 10fs kerrlens modelocked ti. Kerrlens mode locking without nonlinear astigmatism. Control and manipulation of the kerrlens modelocking dynamics in lasers shai yefet department of physics ph. Experimental setup of the kerr lens mode locked klm alexandrite oscillator is schematically depicted in fig.
Kerr lens modelocking how is kerr lens modelocking. This reduction in mode size inside the crystal acts as a soft aperture leading to kerrlens modelocking. A zshaped resonator consists of two curved mirrors, m1 and m2, with the radius of curvature r 10 cm, and two output couplers, m3 and m4, having transmissions of 2 and. In addition, a general description is given to other modelocking techniques, which preceded kerr lens modelocking. Analysis of laser cavities with selfstarting kerrlens. In addition, sibbett and two research colleagues first demonstrated the kerrlens modelocking technique in a titaniumsapphire laser. Two technologically important consequences of the kerr effect are selffocusing, used for laser modelocking, and selfphase modulation, used for compressing laser pulses to fewcycle duration. Specifically, we provide a detailed description of the theoretical and experimental physics of a kerr lens mode locked klm ti. The general principle behind kerrlens mode locking is sketched in fig. Intensity autocorrelation of a representative pulse width recorded at 607 nm from the kerrlens modelocked pr. Simulation of kerr lens modelocking behavior in sagittal.
A meanfield model for kerr lens modelocking springerlink. Investigation of the kerrlens mode locking ability of cr. Kerrlens and additive pulse mode locking soft aperture hard aperture gain. A simple analytical formalism yields closedform expressions for the depth of passive amplitude modulation. Cavitymode analysis of a kerrlens modelocked laser with. In a nutshell, kerrlens mode locking provides a means for producing femtosecond 1018 s laser pulses by conveniently exploiting a nonlinear optical effect in the laser crystal itself. At the repetition rate of 96 mhz, several configurations have been studied to achieve either pulse duration of 40 fs with average powers up to the watt level or shorter pulse duration down to 32 fs. Modelocking is a straightforward method to generate femtosecond pulses and kerr lens effect is a widespread way to lock the oscillator cavity modes.
In the absence of atmospheric air, such oscillators have recently yielded average powers as high as 275 w and pulse energies of 80. Analytic theory of additive pulse and kerr lens mode locking. On the basis of this result the optimal cavity configuration for kerrlens mode locking is proposed that allows to achieve a sub100 fs pulse duration. Activepassive modelocking as a preface to the kerr lens modelocking mechanism, we provide a general and intuitive description of the modelocking techniques that preceded kerr lens modelocking. The dispersive mirrors were described in detail in 53. In the second stage, we demonstrate a kerr lens mode locked folded cavity using a planar nonbrewster ti. A pulse that builds up in a laser cavity containing a gain medium and a kerr medium experiences not only selfphase modulation but also self focussing, that is nonlinear lensing of the laser beam, due to the nonlinear refractive index of the kerr medium. Energy scaling of kerrlens modelocked thindisk oscillators. This effect is called selffocusing and has important implications for passive mode locking of lasers kerr lens mode locking and for optical damage of media catastrophic selffocusing. The rp photonics buyers guide contains 6 suppliers for kerr lens mode locked lasers. A simple analytical formalism yields closedform expressions for the depth of passive amplitude modulation introduced by either the spatial gain profile or a hard aperture inserted in the resonator. This method allows the generation of pulses of light with a. Znse active medium predicts the strong defocusing cascaded secondorder nonlinearity within 2000 3000 nm spectral range.
Kerr lens mode locking is a technique of passive mode locking a laser, using an artificial saturable absorber based on kerr lensing in the gain medium. A laser operated in this way is sometimes referred to as a femtosecond laser, for example in modern refractive surgery. The generation of 72fs hyperbolic secant pulses centered at 1050nm with 17. Kerrlens modelocked thindisk oscillator with 50% output. The main role of kerrlens mode locking is to provide stability against noise buildup. Kerr lens modelocking of a subpicosend optical parametric oscillator. Yvo 4 laser with pulse durations as short as 80 fs at a pulse repetition frequency of 79 mhz. Yag crystal is used for gain medium and it was pumped directly by stacked ld bar. Thesis submitted to the senate of barilan university. With the help of a semiconductor saturable absorber mirror, stable modelocking with an average output power of 85mw at a repetition rate of 1mhz is realized. Modelocking is a technique in optics by which a laser can be made to produce pulses of light of extremely short duration, on the order of picoseconds 10.
If the electronic kerr effect with response time of a few femtoseconds or less is used, a fast saturable absorber has been created. When it was introduced in 1994, this was the first commercial ti. Section 4 describes the fundamental concepts of kerr lens modelocking. The theoretical calculation for nonlinear refractive index in cr. Selffocusing in conjunction with an intracavity aperture creates a powerdependent amplitude modulation in laser oscillators, which allows passive mode locking. This ratio may be en hanced in klm at the expense of cavity stability. In this study, we report on pure kerrlens modelocked yb. We propose a new meanfield or master equation capable of describing transverse effects, pulse evolution and nonlinearity in an appropriate cavity. Kerr lens mode locking is a powerful and wellknown method for generation of ultrashort pulses from solidstate lasers 10 and was adopted as mode locking mechanism in this work. Adaptation to the edge of chaos in a selfstarting kerrlens modelocked laser 403 length l 9 mm.
Such combined mechanism has the same effect as a saturable absorber. For the first time to our knowledge, with a combination of 488, 476 and 458nm lines from argonion laser as a pump source, 58fs pulses centered at 845 nm were generated. Control and manipulation of the kerrlens modelocking. Period doubling of an 84mhz repetitionrate kerrlens modelocked ti. In addition the position of a hard or soft aperture similar as a fast saturable absorber in a klm laser is discussed.
Directly diodepumped, kerrlens modelocked, fewcycle cr. Sesam allowed modelocking to selfstart, the resultant pulse duration of 180 fs was significantly longer than allowed by the gain medium. Pdf the abcdmatrix formalism is generalized for the description of. Kerrlens modelocking klm is a method of mode locking lasers via the nonlinear optical kerr effect. Adaptation to the edge of chaos in a selfstarting kerr. This method allows the generation of pulses of light with a duration as short as a few femtoseconds the optical kerr effect is a process which results from the nonlinear response of an optical medium to the electric field of an electromagnetic wave. In this section, the mechanism of pulse formation is described in a qualitative and intuitive manner. Lisgaf laser that based on a compact cavity geometry. This configuration leads to a spatial sweeping action of a singlepeaked pulse.