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. Sesam allowed mode locking to selfstart, the resultant pulse duration of 180 fs was significantly longer than allowed by the gain medium. Apr 24, 2001 the mechanism for selfstarting operation of kerr lens mode locking laser is studied. Kerr lens mode locking klm is another technique that can be realized in a simple cavity without the need of an auxiliary cavity. The ariati series are broadband, kerrlens mode locked femtosecond oscillators with an integrated pump laser. Laubereau physik department ell, technische universitdt munchen, 85748 garching. Yag is an attractive material for highpower and ultrashort pulse laser because of its high quantum efficiency exceeding 90% and wide gain spectrum larger than about 10 nm. The sml laser needs no any additional active or passive devices in the cavity, so the cavity losses are significantly decreased, and the. Adaptation to the edge of chaos in a selfstarting kerr lens mode locked laser 403 length l 9 mm. Kerrlens mode locking is caused by the selffocusing. One of the most successful schemes is called kerr lens mode locking klm, also sometimes called self mode locking. The optical kerr effect is a process which results from the nonlinear response of an optical medium to the electric field of an.
Highresolution optical coherence tomographic imaging using a. Compact efficient multighz kerrlens mode locked diode. To achieve mode locking, it is thus necessary to lock the frequency separation of the longi tudinal modes to c2land to lock their phases. The repetition rate is about 50 mhz, resulting in a single pulse energy of 30 nj and a peak power of 0. For negative n 2, the nonlinearity is selfdefocusing. Intensity autocorrelation of a representative pulse width recorded at 607 nm from the kerr lens mode locked pr. We propose a new meanfield or master equation capable of describing transverse effects, pulse evolution and nonlinearity in an appropriate cavity. Cavity design of a compact kerrlens modelocking laser. Experimental setup of the kerr lens mode locked klm alexandrite oscillator is schematically depicted in fig. Squier,1 matthew kirchner,2 greg taft,2 kevin shea,2. Kerr lens modelocking of a subpicosend optical parametric.
A mechanism of kerr lens mode locking in fiber laser is proposed and analyzed. General features of this modelocking technique are discussed, and a procedure for the optimization of. Fortrancodes for an analysis of the ultrashort pulse propagation. Kerr lens mode locking klm is a method of mode locking lasers via the nonlinear optical kerr effect. The ring cavity generates ultrashort pulse trains by means of softaperture kerr lens mode locking in either unidirectional or bidirectional lasing mode. Selffocusing in conjunction with an intracavity aperture creates a powerdependent amplitude modulation in laser oscillators, which allows passive mode locking. Mar 03, 2003 an additive kerr medium is used for stable mode locked operation instead of semiconductor saturable absorber mirrors sesam, because kerr effect of the yb. The ariati series feature compact size, userfriendly operation and longterm reliability.
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 in. Lu2o3 thindisk laser oscillators operating in the sub100fs regime. Squier,1 matthew kirchner,2 greg taft,2 kevin shea,2 henry kapteyn,2,4 margaret murnane,2,4 and sterling backus2,3 1department of physics, colorado school of mines, golden, colorado 80401, usa 2kmlabs inc. Generation of 85 fs laser pulses from a diodepumped kerr. Investigation of the kerrlens mode locking ability of cr. On the contrary, kerr lens mode locking is known to support much shorter pulse durations 42, even beyond the emission bandwidthlimit of the laser gain medium 43, 44.
This uses a nonlinear optical process, the optical kerr effect, which results in highintensity light being focussed differently from lowintensity light. Experimental results reveal that the laser system can be characterized in stable singlepulse and multiplepulse mode locked operations. The whole characterization of the realized mode locking laser oscillators is presented with particular attention to the relative intensity noise of the sources. Cagdalo 4 oscillator optically pumped by a bright fiber laser p. Energy scaling of kerrlens modelocked thindisk oscillators. However, no matter what kind of mode locking mechanisms are applied, either kerr lens mode locking klm or passive mode locking with sesam or cnt, the shortest pulse. Kerrlens modelocking klm is a method of modelocking lasers via the nonlinear optical kerr. The general principle behind kerrlens mode locking is sketched in fig. With kerr lens mode locking this pulling is achieved by exploiting a kerr lens that persists only in the presence ofan intense short pulse. Kerr lens mode locking is a technique for mode locking a laser, exploiting nonlinear selffocusing. Central wave length tunability as broad as 89 nm 736825 nm is. All these research works utilize the basic fourmirror fold cavity geometry, which includes a brewstercut gain medium, two astigmatismcompensating offaxis concave mirrors, two flat mirrors, and a prism pair for.
Since klm relies on the nonresonant kerr nonlinearity, it is independent of the lasing wavelength and bandwidth and gives ultrafast response. Pulses with durations as short as 14 fs and bandwidths of. This has led to a number of mode locking techniques to obtain such pulses, for example acoustooptic, injection, synchronouspump, collidingpulse mode locking, and kerr lens mode locking. The general principle behind kerr lens mode locking is sketched in fig.
Multipulse operation and limits of the kerrlens modelocking. 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. We introduce a novel concept for optical frequency measurement and division which employs a kerr lens, mode locked laser as a transfer oscillator whose noise properties do not enter the measurement process. Its strength lies in the very fast response and the fact that no special saturable absorber medium is required. Using the latter two techniques, pulses of less than 100 fs duration can be readily obtained.
Control and manipulation of the kerrlens modelocking. We demonstrate the compact efficient multighz kerr lens mode locking in a diodepumped nd. Resonators for kerr lens mode locked lasers are studied with the help of an analytical model, and a new design procedure is presented. Instead, the method of nonlinear polarization rotation is typically used, although semiconductor saturable absorbers are also common. 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. Active mode locking with picosecond pulse duration was realized in 2000, semiconductor saturableabsorber mirror sesam mode locking was demonstrated in 2005, and kerr lens mode locking was achieved in 2009. We report a direct bluediodepumped wavelength tunable kerr lens mode locked ti. Fiber lasers cannot utilize the kerr lens mode locking used for ti. Saturable gain and loss the passively mode locked dye laser some common dyes and their corresponding saturable absorbers colliding pulses have a higher peak intensity. A 15ghz mode spacing optical frequency comb based on a kerr lens mode locked yb. Rp photonics encyclopedia kerr lens mode locking, hard.
The collidingpulse mode locked cpm laser a lens and a lens kerr lens mode locking kerr lensing is. Dispersion compensation and heterodyne noise rejection are demonstrated to yield in situ images of biological tissues with 3. In the case of bidirectional mode locking, the repetition rates of the two outputs can be made identical or slightly different, depending on the cavity alignment. What links here related changes upload file special pages permanent link page. Artificial saturable absorber modelocking apm and klm kerrlens modelocking klm chapter 7 pdf 1. The laser used a slightly modified standard delta cavity. Kerrlens mode locking is caused by the self focusing. Kerrlens modelocked highpower thindisk oscillators.
A kerr lens mode locked laser has been designed with thinrod yb. Files are available under licenses specified on their description page. On the other hand, kerr lens modelocking is advantageous for generating short pulses because it provides an instantaneous response and a high modulation depth 15. Multipulse operation and limits of the kerrlens modelocking stability vladimir l. Pulses as short as 35 fs were generated at an average output power of 1. To the best of our knowledge, this is the highest single pulse energy ever produced from a mode locked. N, birmingham, alabama 35203, usa 2ipg photonics corporation, 50 old webster rd, oxford, massachusetts 01540, usa 3center for optical sensors and. In the absence of atmospheric air, such oscillators have recently yielded average powers as high as 275 w and pulse energies of 80. However, thekerrlensmodelocked klmresonatordesignis challenging because it typically requires operation close to a stability edge for continuouswave cw operation. All structured data from the file and property namespaces is available under the creative commons cc0 license. In addition, a general description is given to other mode locking techniques, which preceded kerr lens mode locking. The article on passive mode locking explains how a saturable absorber leads to mode locking.
This arm of the cavity also contained a vertical slit to enable a hardaperture kerrlens modelocking. Analysis of laser cavities with selfstarting kerrlens mode. By careful arrangement of an aperture in the laser cavity, this effect. It could be realized in active photoniccrystal fibers with finite number of the air holes hexagonally arranged. Cya laser by separating the gain medium and kerr medium. Pulses as short as 85 fs at a central wavelength of 1074. Our research is development of highaverage power kerr lens mode locked. Directly diodepumped, kerrlens mode locked, fewcycle. The corresponding spectral profile is shown in fig.
Al 2o 3 oscillator, optimized for minimal coherence length, is demonstrated as a highpower source for highresolution optical coherence tomographic imaging. In this experiment this will be accomplished by picking o a bit of the outcoupled light, shifting it up or down in frequency by c2l, then reinjecting this into the laser cavity. Such combined mechanism has the same effect as a saturable absorber. It is suitable for generating fewfemtosecond laser pulses. Passive mode locking 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. It is developed with a view to modeling kerr lens mode locking, but promises much wider applicability.
Astigmatism in gaussianbeam selffocusing and in resonators for kerrlens mode locking. Individual modes were clearly resolved by a commercial spectrometer. It generates pulses with a duration of 30 fs at a central wavelength of 1048 nm and a repetition rate of 124 mhz. Following the demonstration of the first kerr lens mode locked klm tdl 19, similar scaling laws were demonstrated for this alternative mode locking technique resulting in average output powers up to 270 w in 330fs pulses utilizing yb. In this section, the mechanism of pulse formation is described in a qualitative and intuitive manner. We experimentally demonstrate that this method opens up the route to phaselink signals with arbitrary frequencies in the optical or microwave range while their frequency stability is. On the contrary, kerr lens mode locking is known to support much shorter pulse durations 23, even beyond the emission. 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.
A high spatial and spectral quality is achieved, close to the diffraction and fourier transform limitations. A zshaped resonator consists of two curved mirrors, m1 and m2, with the radius of curvature r 10 cm, and two. Analytical design of symmetrical kerrlens modelocking laser cavities. Kerr lens modelocking is initiated by introducing an intensity spike by rapidly moving one of the prisms. By theoretical calculation of the group velocity dispersion in the laser gain, the compensation was employed for the realization of the continuouswave mode locked laser at the wavelength of 604 nm with the pulse width of 1. These are the shortest pulses directly emitted from a thindisk laser oscillator. Sml, or kerr lens mode locking klm, has been successfully applied to the generation of ultrashort pulses in solid state lasers. Adaptation to the edge of chaos in a selfstarting kerrlens.
When pumping with the 532nm beam alone, we are able to initiate and sustain modelocking at a pump power. This peculiar lasing principle builds on a slight difference in optical cavity length between two counterpropagating lasing modes due to kerr lensing. Ylf laser, initiated by means of a liquid saturable absorber. Dispersive mirrors compress the pulses to a duration of 190 fs assuming sech2 shape. Benefiting from the fruitful combination of the kerr lens mode locking scheme and the broad emission of the. 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. Kerr lens mode locking has enabled the generation of the shortest pulses with durations down to. The theoretical calculation for nonlinear refractive index in cr. Directly diodepumped, kerrlens modelocked, fewcycle cr. Generation of 35fs pulses from a kerr lens modelocked yb.
In this study, we report on pure kerrlens modelocked yb. The cavity is designed to make the cavity less lossy ifthe kerr lens is present. Sf57 glass is used to stabilize the mode locked oscillation to decrease the intracavity loss to increase the oscillation bandwidth for transform limited pulse generation. Without any gvd compensation, the single pass gvd for the 9 mm ti. This method allows the generation of pulses of light with a duration as short as a few femtoseconds. Passive mode locking with an ideally fast saturable absorber semiconductor and dye lasers. Pdf the abcdmatrix formalism is generalized for the description of selffocusing and radially varying. In addition the position of a hard or soft aperture similar as a fast saturable absorber in a klm laser is discussed. If the electronic kerr effect with response time of a few femtoseconds or less is used, a fast saturable absorber has been created. 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. Znse active medium predicts the strong defocusing cascaded secondorder nonlinearity within 2000 3000 nm spectral range.
Kerrlens mode locking klm is another technique that can be realized in a simple cavity without the need of an auxiliary cavity. Kerr lens and additive pulse mode locking soft aperture hard aperture gain. Cagdalo 4 oscillator optically pumped by a diffraction limited fiber laser. Currently, the generation of ultrashort optical pulses is dominated by the kerr lens mode locked ti. The latter effect causes a reduction in the beam size for high optical intensities. The other cavity arm had a pair of sf10 prisms p1 and p2 for dispersion compensation separated by 37 cm. It is capable of producing up to a 60nm broadband spectrum and highpower mode locked output. Our research is development of highaverage power kerr lens mode locked yb. These developments were accompanied by many challenges, including the initiation of modelocking, thermal lensing and the oscillator stability.
Yvo 4 laser with a simple linear cavity without the need of any additional components. Thesis submitted to the senate of barilan university. Kerr lens modelocking of a subpicosecond optical parametric. The laser emits the shortest pulses generated by a thindisk laser oscillator, equal to the shortest pulse duration obtained by ybdoped bulk oscillators. Lyso laser with 61fs pulse duration wenlong tian, 1 zhaohua wang,2, long wei, yingnan peng, jinwei zhang,2 zheng zhu, 3 jiangfeng zhu,1 hainian han,2 yulei jia, lihe zheng,4 jun xu,4 and zhiyi wei2,5 1school of technical physics and optoelectronics engineering, xidian university, xian 710071, china 2beijing national laboratory for condensed matter physics. 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. A bidirectional dualcomb ring laser for simple and robust. Ylf laser as a source of femtosecond pulses in the midinfrared ferda canbaz, ismail yorulmaz, and alphan sennaroglu opt. Several types of cavity structures with which selfstarting operation of kerr lens mode locking lasers may be achieved are presented. Al 2o 3 laser achieved by use of an extended cavity design is demonstrated. Two dispersive mirrors introduce a group delay dispersion gdd of. Yag thindisk oscillator operating in the regime of positive intracavity groupdelay dispersion gdd.
Lecture notes ultrafast optics electrical engineering and. Measurements were taken in order to determine the mechanism behind the mode locking bias in these oscillators. Threeelementcavity enables kerrlens modelocking at 20. Yag crystal is used for gain medium and it was pumped directly by stacked ld bar. A meanfield model for kerr lens modelocking springerlink. Kerrlens, modelocked lasers as transfer oscillators for. Zns laser sergey vasilyev,1,igor moskalev,1 mike mirov,1 sergey mirov,1,3 and valentin gapontsev2 1ipg photonicsmidinfrared lasers, 1500 1st ave. Chapter 5 active mode locking forsimplicity, we assume, that the laser operates inthe transverse fundamental modes and, therefore, we only have to treat the longitudinal modes of the laser similar to a simple plane parallel fabryperot resonator figure. We demonstrate a selfstarting kerr lens mode locked klm yb. Pdf feasibility of kerrlens mode locking in fiber lasers. Control and manipulation of the kerrlens modelocking dynamics in lasers shai yefet department of physics ph. This has led to a number of modelocking techniques to obtain such pulses, for example acoustooptic, injection, synchronouspump, collidingpulse modelocking, and kerr lens modelocking. Mode locking thresholds as low as 156 mw are achieved.
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