The latter can be either due to the pumplaser mode overlap soft aperture or a physical hard aperture. Pulses as short as 85 fs at a central wavelength of 1074. Kerr lens and aperture acts as a fast saturable absorber, then a fast passive gain modulation is obtained 5. 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. Znse lasers 4, kerrlens mode locking klm in polycrystalline cr. Kerr lens modelocking of solid state lasers with thermal lensing. Rp photonics encyclopedia kerr lens mode locking, hard. 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. This uses a nonlinear optical process, the optical kerr effect, which results in highintensity light being focussed differently from lowintensity light.
We demonstrate a kerr lens modelocked folded cavity using a planar nonbrewster ti. Multipulse operation and limits of the kerrlens modelocking stability vladimir l. The collidingpulse modelocked cpm laser a lens and a lens kerrlens modelocking kerrlensing is a. Osa kerrlens mode locking above a 20 ghz repetition rate. Jan 02, 20 the kerr lens mode locking strength at the curved mirror was calculated over the stable range. Mode locking can be achieved in a laser by the use of an active element. The average output power was 80 mw under a 4w diode pump power. Experimental setup of the kerr lens mode locked klm alexandrite oscillator is schematically depicted in fig. The intensity fluctuations in laser startup are not intense enough to induces kerr lensing 6,7, thus acoustooptic modulation, additive pulse mode locking, impulsive starting i.
Control and manipulation of the kerrlens modelocking. The results indicate that the astigmatism is best compensated so. Many different models have been used to describe pulse propagation in mode. Control and manipulation of the kerr lens mode locking dynamics in lasers shai yefet department of physics ph. Pdf kerrlens mode locking without nonlinear astigmatism. Analytic theory of additive pulse and kerr lens mode locking. Kyw in the laser cavity, where not only the pump threshold to start mode locking but also the stable regions to maintain mode locking can be wellcontrolled. Analytical design of symmetrical kerrlens modelocking laser. Paper open access simulation of femtosecond pulse in a. Kerrlens 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. The latter produces the shortest pulses and hence we shall be concerned with the dynamics of passive ml lasers. A new technique called kerr lens mode locking klm has recently been developed which achieves fast saturable absorber action using selffocusing and.
We demonstrate a kerr lens mode locked folded cavity using a planar nonbrewster ti. Starting dynamic, selfstarting condition and modelocking threshold in passive, coupledcavity or kerrlens modelocked solidstate lasers. The latter effect causes a reduction in the beam size for high optical intensities. In the case of kerrlens modelocking, a mechanism for creating multiple pulses is enhanced kerrlensing at the overlap of pulses in the ti. Initially, mode locked tdls relied on semiconductor saturable absorber mirrors sesams. Exploring ultrafast negative kerr effect for modelocking. Our research is development of highaverage power kerrlens modelocked. Saturable gain and loss the passively modelocked dye laser some common dyes and their corresponding saturable absorbers colliding pulses have a higher peak intensity. Selffocusing in conjunction with an intracavity aperture creates a powerdependent amplitude modulation in laser oscillators, which allows passive mode locking. The results indicate that the astigmatism is best compensated so that the stable range of x and y. We demonstrate a femtosecond kerrlens modelocked cr. However, the wellestablished theoretical framework is sometimes beyond the scope of highpower oscillators, including recently developed thindisk. Measurements were taken in order to determine the mechanism behind the modelocking bias in these oscillators.
Kerrlens modelocked highpower thindisk oscillators. This has led to a number of modelocking techniques to obtain such pulses, for example acoustooptic, injection, synchronouspump, collidingpulse modelocking, and kerrlens modelocking. In this section, the mechanism of pulse formation is described in a qualitative and intuitive manner. 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. To date, passive mode locking methods such as kerr lens mode locking have been used to generate sub5fs pulses 1,2. The general principle behind kerrlens mode locking is sketched in fig. Pdf kerr lens mode locking christian spielmann academia. Specifically, we provide a detailed description of the theoretical and experimental physics of a kerr lens mode locked klm ti.
If you have a user account, you will need to reset your password the next time you login. Get pdf abstract we present a compact, kerrlens modelocked oscillator consisting of a threeelement optical setup and demonstrate femtosecond pulse generation at a repetition rate of 23. Lyso laser is around 780 fs which is far beyond the limitation of. Kerrlens and aperture acts as a fast saturable absorber, then a fast passive gain modulation is obtained 5. However, no matter what kind of modelocking mechanisms are applied, either kerrlens modelocking klm or passive modelocking with sesam or cnt, the shortest pulse generated from the yb. Lisgaf laser that based on a compact cavity geometry. One of the most successful schemes is called kerrlens modelocking klm, also sometimes called self modelocking.
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. Thesis submitted to the senate of barilan university. By careful arrangement of an aperture in the laser cavity, this effect. To date, passive mode locking methods such as kerrlens mode locking have been used to generate sub5. The basis of the technique is to induce a fixedphase relationship between the longitudinal modes of the lasers resonant cavity. Using the latter two techniques, pulses of less than 100 fs duration can be readily obtained. The collidingpulse mode locked cpm laser a lens and a lens kerr lens mode locking kerr lensing is a type of saturable absorber. The general principle behind kerr lens mode locking is sketched in fig. 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.
Kerr lens modelocking of a subpicosecond optical parametric. Resolving the buildup of femtosecond modelocking with. Our research is development of highaverage power kerr lens mode locked. Ultrashort pulse laser oscillators have been studied for the last halfcentury. 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. Since klm relies on the nonresonant kerr nonlinearity, it is independent of the lasing wavelength and bandwidth and gives ultrafast response. Kerrlens mode locking klm is another technique that can be realized in a simple cavity without the need of an auxiliary cavity. Passive mode locking with an ideally fast saturable absorber semiconductor and dye lasers. Kerrlens modelocking klm is essentially a process of mimicking a fast saturable absorber inside a laser cavity by a combination of selfaction of the laser beam due to the optical kerr effect together with spatial aperturing 1517. Generation of 85 fs laser pulses from a diodepumped kerr. 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. Active and passive mode locking cornell ece4300 fall 2016 duration. A high spatial and spectral quality is achieved, close to the diffraction and fourier transform limitations. Analytical design of symmetrical kerrlens modelocking laser cavities.
A meanfield model for kerr lens modelocking springerlink. It is developed with a view to modeling kerr lens modelocking, but promises much wider applicability. 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. 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. The optical kerr effect is a process which results from the nonlinear response of an optical medium to the electric field of an. In the present case, mutual kerrlensing takes place in a zns crystal located at the center of the cavity, as shown in fig. Recently the optical kerr effect has been used for mode locking solidstate lasers to generate ultrashort laser pulses. In addition, a general description is given to other modelocking techniques, which preceded kerr lens modelocking. We demonstrate a femtosecond kerr lens mode locked cr. One of the most successful schemes is called kerr lens mode locking klm, also sometimes called self mode locking. Kerrlens mode locking without nonlinear astigmatism.
The design and alignment of these laser resonators have thus far been theoretically supported by the conventional analysis of beam propagation. General features of this modelocking technique are discussed, and a procedure for the. Kerrlens modelocking klm is a well developed technique for modelocking which has been widely used in femtosecond ti. Control and manipulation of the kerrlens modelocking dynamics in lasers shai yefet department of physics ph. We propose a new meanfield or master equation capable of describing transverse effects, pulse evolution and nonlinearity in an appropriate cavity. Geometrical analysis of kerrlens modelocking for highpeak. Kerr lens mode locking klm is a method of mode locking lasers via the nonlinear optical kerr effect. Kyw in the laser cavity, where not only the pump threshold to start modelocking but also the stable regions to maintain modelocking can be wellcontrolled. In addition, a general description is given to other mode locking techniques, which preceded kerr lens mode locking. In the same framework, self starting of passive mode locking has the thermodynamic signi.
Femtosecond kerrlens modelocked thindisk oscillators constitute a peak and average power scalable oscillator concept. 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. Ramanassisted broadband modelocked laser scientific reports. It is suitable for generating fewfemtosecond laser pulses. Section 4 describes the fundamental concepts of kerr lens mode locking.
The availability of tdl crystals with broader gain emission bandwidths 14 allowed reducing the pulse duration of tdls from initially 680 fs 4 to 49 fs, which has been delivered at 2 w average output power 9. In the present case, mutual kerr lensing takes place in a zns crystal located at the center of the cavity, as shown in fig. In the case of kerr lens mode locking, a mechanism for creating multiple pulses is enhanced kerr lensing at the overlap of pulses in the ti. Experimental setup of the kerrlens modelocked klm alexandrite oscillator is schematically depicted in fig. Multipulse operation and limits of the kerrlens modelocking. The laser used a slightly modified standard delta cavity. We demonstrate a kerrlens mode locked folded cavity using a planar nonbrewster ti. Passive modelocking using saturable absorbers an intracavity saturable absorber is able to fix phase of cavity modes variations slow saturable absorber fast saturable absorber kerrlens effect. Kerr lens mode locking without nonlinear astigmatism. Initially, modelocked tdls relied on semiconductor saturable absorber mirrors sesams. Kerrlens modelocking klm is a method of modelocking lasers via the nonlinear optical kerr effect. Paper open access simulation of femtosecond pulse in a kerr. Pdf the abcdmatrix formalism is generalized for the description of selffocusing and radially varying pump power in a nonparabolic.
The kerrlens modelocking strength at the curved mirror was calculated over the stable range. Kerrlens mode locking klm, simulating fast saturable absorber action, can achieve sub20fs pulses from ti. Kerr lens mode locking klm is another technique that can be realized in a simple cavity without the need of an auxiliary cavity. Our method uses a novel cavity folding in which the intracavity laser beam propagates in two perpendicular planes, such that. Section 4 describes the fundamental concepts of kerr lens modelocking. Kerr lens mode locking is a technique for mode locking a laser, exploiting nonlinear selffocusing. This method allows the generation of pulses of light with a. It has been recently understood that mode locking of lasers has the signi. This method allows the generation of pulses of light with a duration as short as a few femtoseconds. 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 intensity fluctuations in laser startup are not intense enough to induces kerr lensing 6,7, thus acoustooptic modulation, additive pulse modelocking, impulsive starting i. Ultrashort pulses from kerrlens modelocked oscillators have inspired a variety of applications. 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 generated from the yb.
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