Ultrafast lasers are typically defined as any pulsed laser producing pulse widths less than 10 ps (picosecond lasers), down into the femtosecond region (femtosecond lasers) and beyond, which are commonly referred to as ultrashort pulses (ultrashort pulse lasers).
‘Ultrafast Lasers’ is a term that can refer to a number of various types of lasers. However, for our purposes, we are referring to mode-locked fiber lasers. Our ultrafast lasers are produced by mode locking many phase-locked longitudinal modes from a broadband laser or a material with a large gain bandwidth. Because of this, mode locking induces a beat frequency which results in picosecond or femtosecond duration laser pulses. Furthermore, these ultrafast laser pulses are unique for their extremely high peak power and, combined with the ultrashort pulses, are ideal for a number of applications. For example: non-thermal ablation, micromachining, and non-linear spectroscopy including CARS and two-photon microscopy.
Picosecond Lasers – Picosecond Lasers emit laser pulses with a pulse duration in the picosecond range (one-trillionth of a second, or 10 -12 seconds). Given a particular value for pulse energy, the laser pulse’s peak power increases as the pulse duration gets shorter. So, a laser with shorter pulses, such as a picosecond laser, can achieve much higher peak powers when compared to longer pulsed nanosecond or millisecond pulsed lasers.
Femtosecond Lasers – Femtosecond lasers emit optical pulses with a pulse duration below 1 picosecond, in the femtosecond range. A femtosecond (fs) is one quadrillionth (one millionth of one billionth) of a second or 10−15 seconds. Since lasers producing less than 10 ps pulses are considered Ultrafast Lasers or Ultrashort Pulse Lasers, femtosecond lasers fall firmly in this category.
Our Ultrafast Laser Products
We offer a selection of ultrafast mode-locked lasers with pulse widths as short as 100 femtoseconds (100fs) and up to 10 picoseconds (10ps). They produce a peak pulse energy up to 60 microjoules (60µJ) and pulse repetition rates up to 80 MHz. These lasers are typically available in the near infrared wavelength region. However, frequency doubling allows the generation of visible outputs in the green spectral region. With many options and customization capabilities, we’re sure to have a solution for your unique problem.
RPMC is your Ultrafast Laser Supplier! We have supplied many fiber-based femtosecond laser systems to various researchers, laboratories, and materials science development teams around the country. Often, the researchers we work with don’t have extensive laser experience, and rely on us to help them choose the best laser for their application or project.
Benefits of Ultrafast Lasers
The higher peak powers provided by shorter pulsed lasers result in faster removal rates within the same material, as more energy is transferred to the material in less time, and less energy can absorb in the surrounding material, generating less heat. These lasers, with high peak powers (often several megawatts), cause the atomic bonds of the material to break. This break is referred to as a Coulomb explosion, which is a ‘cold processing’ (athermal ablation or non-thermal ablation) method, as opposed to a more conventional thermal ablation method inherent to longer pulsed lasers (e.g., nanosecond pulsed lasers).
In contrast to non-thermal ablation, traditional thermal ablation relies on localized heating of the material, resulting in the melting, and vaporization of the material’s molecules and atoms. This processing technique is detrimental to certain laser applications. Femtosecond lasers have certain technical advantages versus picosecond lases. However, picosecond lasers tend to have much more attractive pricing, while still offering high peak powers and high average powers in a less complicated system.
Ultrafast Lasers are perfect cold ablation of many materials, such as plastics, polymers, PET, composites, glass, diamonds, ceramics, metals, and various coatings. Ultrafast lasers can even perform well with layered substrates. Cold ablation allows for high-precision material removal without heating surrounding area. Thus, ultrafast lasers will not produce heat affected zones (HAZ) or significant material splatter recast. Another benefit provided by ultrafast lasers is the reduction or elimination of any post-processing or cleaning.
In recent years, femtosecond fiber lasers have started replacing bulkier, more complicated, water-cooled ti sapphire lasers. These air-cooled ultrafast fiber lasers, take up less space and allow you to place the controller in a rack mount, for example, while positioning the smaller laser head right where you need it.
At one-tenth the volume, twice the power, and half the cost, our fs Fiber Lasers are perfect replacements for old, outdated Ti:Sapphire lasers. With useful wavelengths like 920, 1040, and 1064nm, you aren’t paying extra for unnecessary wavelength tunability. With a compact, air-cooled, maintenance-free design, and an industry-standard beam height, you’ll see a fast ROI with less downtime and more room to breathe after easily dropping one of these plug-and-play fs Fiber Lasers into your old Ti:Sapphire laser footprint.
Peak Power and Average Power in ns and Sub-ns Lasers
A significant and well-recognized difference between lasers and conventional, incoherent light sources, is the ability to concentrate laser emission in short pulses, with durations going down to a few femtoseconds, containing potentially only a few optical cycles. Technically, you can drive an incoherent LED source using current pulses, allowing the emission of light pulses down in the nanosecond range. However, each pulse would have a maximum power (i.e. a peak power) equal to the average power of the same device if a continuous bias were applied. Only laser cavities can concentrate the stored energy within active materials in such a way to achieve peak powers orders of magnitude higher than their average power, up to the exceptional PW-level recently reported in research publications. The extremely high peak power levels achievable by pulsed laser sources are among the main reason for their success in many of the applications which have emerged in the last decades. Therefore, a precise estimation of the laser peak power, given other operational parameters such as average power, pulse duration, and repetition rate, is fundamental to select the best option for a particular application among the different commercial alternatives. In principle, it is quite simple to calculate the peak power, considering the actual temporal profile of the laser pulse. By assuming a train of continuously repeated, periodical, square pulses with repetition rate fR, pulse duration tP and average power PAV, the pulse energy EP and peak power PP calculations are trivial, with pulse energy provided by the ratio between average power and repetition rate and peak power provided by the ratio between energy and pulse duration:
Of course, this simple relationship holds for laser pulses with a square or flat-top temporal profile, which is rather uncommon in practice. Usually, laser pulse temporal profiles are approximated more accurately with bell-shape functions, such as Gaussian profile or Sech2 profile, the latter being relevant mainly for ultrashort pulses obtained by the passive mode-locking regime. In this case, one should redefine pulse duration as being full-width half-maximum (FWHM), a commonly accepted parameter. Since the energy concentration in a Gaussian pulse, with FWHM duration tP, is slightly different from a square pulse with equal pulse duration, one needs to adjust the formula above
Raman Spectroscopy: Why are Picosecond Pulses Superior to Femtosecond?
Raman-based spectroscopy, on the other hand, is an entirely different nonlinear technique, relying on the frequency shift experienced by laser radiation incident on a molecule, related to its rotational and vibrational modes. Not being related to electronic transitions, the Raman shift is relative concerning the irradiating wavelength, and therefore, unless pursuing coherent excitation, laser source tunability is not required. Raman-based spectroscopy, being a nonlinear process, usually requires ultrashort pulse generation (e.g., practical TPA set-ups usually require < 300 fs pulse duration). On the other hand, since the Raman gain is generally higher than TPA cross-sections, cheaper and simpler picosecond lasers could be efficiently employed in incoherent Raman spectroscopy. Furthermore, in Raman spectroscopy, the spectral resolution is related to the laser source bandwidth. Therefore, the narrower bandwidths of picosecond lasers represent a remarkable advantage over their femtosecond counterparts. For pulsed laser sources, spectral bandwidths and pulse durations are related by a Fourier-transform relationship, descending from the time-energy Heisenberg uncertainty principle. More precisely, the minimum spectral bandwidth is inversely proportional to the pulse duration. The shorter the pulse duration, the larger the bandwidth for a given temporal pulse profile. For instance, for a pulse duration of ~1 ps at the wavelength of ~1 μm, the minimum FWHM spectral bandwidth is ~1 nm. For pulses ten times longer at the same wavelength (~10 ps), the minimum spectral bandwidth is 10 times narrower (~0.1 nm).
Since the spectral resolution in Raman spectroscopy is related to the spectral bandwidth of the illuminating source, 10-ps-long pulses would potentially provide better spectral resolution than 1-ps-long pulses. On the other hand, longer pulses provide lower peak power for a given average power and repetition rate, and therefore a lower signal and a worse signal-to-noise ratio. An optimal pulse duration of a few picoseconds is generally accepted for typical set-ups as a good trade-off between the different requirements. Moreover, it is important to note that the FWHM spectral bandwidth mentioned above is a minimal value. It is not uncommon for practical lasers to emit pulses with a broader spectrum than the narrowest (transform-limited) theoretical profile due to residual, uncompensated, linear, or nonlinear phase shift.
Femtosecond Lasers for Material Processing and Micromachining Applications
The primary application for femtosecond lasers is micromachining, which can include consumer, medical or R&D applications. Typically, these applications require femtosecond pulses for their cold-ablation affects. Femtosecond lasers are ideal tools for applications where micro-cracks, HAZ, or recasts are detrimental to the integrity or lifetime of the material being processed.
A growing application for femtosecond lasers is in the field of handheld electronics…more specifically cell phones and tablets. Manufactures are experimenting with different materials to make a more robust product. The popularity of ultrafast femtosecond lasers continues to grow in these challenging industrial applications that require cold ablation.
Our femtosecond micromachining lasers can be applied to a variety of industrial processes, including cold ablation, semiconductor processing, stent cutting, laser marking, TFT repair, thin film patterning, marking, dicing, scribing, solar cell cutting, edge isolation, laser deposition, surface patterning, processing volatile materials, or machining hard materials. Femtosecond lasers are also used in various medical procedures within the ophthalmological and dermatological fields
Femtosecond lasers microstructure (groove, cut, drill, micromill, etc.) virtually any material with:
no thermal side-effects such as microcracks, burrs, or recast
lateral features as small as a few um
pulses-on-demand for easy integration into delivery systems
high average power, pulse energy and rep rate for increased ablation rate per pulse
Examples for industrial femtosecond laser micromachining can include:
IMD – medical and biomedical devices (PMMA, PLLA, catheters, stents, pacemakers, guidewires, cutting, drilling, de-coating, etc.)
If you have any questions, or if you would like some assistance please Contact Us here. Furthermore, you can email us at [email protected]to talk to a knowledgeable Product Manager.
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The NPS series of ultrafast lasers is the ultimate solution for OEM integrators and researchers working with nonlinear optics applications like OPO pumping and narrowband Raman spectroscopy. The NPS series boasts remarkable features such as up to 10W average output power, <7ps pulse width, and a 40MHz repetition rate. The transform-limited operation, with a spectral width of <0.3nm, and accurate central wavelengths make these lasers a suitable candidate for highly efficient amplification by Nd-doped DPSS amplifiers.