Picosecond Lasers

Our Picosecond Laser Experience

RPMC Lasers is your preferred Picosecond Laser Supplier, partnering with industry-leading and emerging manufacturers. We have been in business for over 25 years, providing researchers and OEM integrators with the best laser solution for their application. We have fielded 1000s of units for many different applications from micromachining to LIDAR and Bathymetry to medical applications such as tattoo removal and ablation-based surgical procedures.

Deeper Dive into Picosecond Lasers

Peak Power and Average Power in ns and Sub-ns Lasers:

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 f_R, pulse duration t_P and average power P_AV, the pulse energy E_P and peak power P_P 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:

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The Advantages and Disadvantages of Passive vs Active Q-Switching:

• Triggering – One of the significant disadvantages of passive q-switching is that you have no control over when the laser actually pulses. The laser’s pulse repetition rate will be solely dependent on the when the absorber saturates.  This is very much akin to a free-running system which not only cannot be controlled but also can experience pulse to pulse variability or jitter.  An actively q-switched laser, on the other hand, provides the ability to trigger the pulse at a specific time and with a particular pulse repetition rate.  This makes it far easier when synchronizing the laser to other instrumentation, such as a kinematic arm for laser machining or a spectrometer for laser-induced breakdown spectroscopy (LIBS).  It should be noted though that most passively q-switched lasers do contain an internal photodiode that can be used to synchronize to an external device, but this not nearly as flexible as the ability to trigger in.
• Pulse Energy – While some passive q-switches are capable of producing rather large, mJ level, laser pulses, in general active q-switching tends to lead to far larger pulse energies. This is because the q-switch can be actively controlled to allow for the maximum shutter time needed for full population inversion.  As a result, the q-switch can be timed to open with the same period as the decay lifetime of the gain medium’s metastable state resulting in the maximum possible pulse energy.   By contrast with a passive q-switch once the absorber has saturated it will release all of the stored energy regardless of whether or not maximum population inversion has been achieved.

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Why is a Low Jitter Feature Important in Actively Q-Switched DPSS Lasers?

In actively Q-switched lasers, the user controls the pulsed laser output, so that no laser pulse emission occurs without providing a proper input signal, aka “the trigger”. Due to the trigger signal propagation through the interface electronics, the Q-switch driver chain, and the laser resonator build-up time, a time delay (Td) is present between the externally-supplied trigger signal and the actual laser pulse emitted by the laser source. The Td can show fluctuations if any electronics or optics involved in the pulse generation process have a functional variance in time.

The parameter Td is very relevant in the timing management of some applications. You must consider both the time delay (Td) and a time jitter (Tj), which is a statistical variation of the time delay depending mostly on:

• electrical noise in the trigger-chain
• pulse-to-pulse fluctuation of trigger-chain electrical parameters
• laser pulse build-up time-mechanism and associated fluctuations.
• fluctuation of rising (-falling) edge temporal profile of the trigger signal

Because of the jitter phenomena, the actual value of the time delay is statistically altered. Therefore, the laser pulse emission event happens (in the vast majority of cases) inside a normal time distribution, defined by an average time delay Td and a standard deviation value Tj (i.e 68.2 out of 100 pulses develop in the time interval Td ±Tj).

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What is a Thin Disk Laser, and What Advantages do They Offer?

A thin disk laser is a type of diode-pumped solid-state (DPSS) laser technology in which the gain medium is comprised of a thin disk of typically Yb:YAG crystal. The thickness of one of these disks (typically 150µm to 200µm thick) is substantially smaller than the beam diameter. This feature allows not only the ability to easily scale up power via pump beam diameter, but also provides a large surface area for heat dissipation. For example, the VaryDisk Series platform is a high energy, multi-milli-Joule laser system for laboratory investigations or industrial use. This is a thin disk regenerative amplifier for amplification of femtosecond, picosecond or nanosecond pulses with amplification factors in the order of 10⁶.

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Picosecond Applications

The picosecond laser benefits make them a good fit for many applications. Typically, various forms of micromachining and material processing come to mind, as mentioned above. The reduction of HAZ and elimination of post-processing makes these lasers desirable for processing of many materials, especially sensitive materials, including medical devices, where rough edges and pits can lead to collection and growth of bacteria, for example. Pico lasers also allow for very fine features to be machined without deformation of the surrounding material. The same is true for femtosecond lasers. However, the picosecond laser cost tends to be much more attractive, with high peak powers and higher average powers available at a lower price, and a less complicated system.

Some other applications that benefit from high peak power picosecond pulsed lasers include various medical applications, such as tattoo removal, pigment removal / pigment reduction, hair removal, and other ablation-based surgical procedures. Laser microscopy, optical parametric oscillators (OPO) pumping, time-of-flight (ToF) LIDAR, pump-probe measurements, and optical fiber communications all benefit from the used of picosecond pulsed lasers. Below we will detail some picosecond laser application examples and links to more in-depth articles:

Laser Material Processing:

Laser material processing includes a wide range of applications including laser scribing, laser drilling, laser cutting, laser marking, thin film removal, laser surface treatment, and much more. One thing most of these applications share is the benefit of utilizing very short light pulses in the picosecond and short nanosecond range (as well as femtosecond for certain applications), which provide high peak power for a particular pulse energy.

Typically, nanosecond pulses are too long, as there is a significant build up of heat in the surrounding material, causing a more prominent heat affected zone (HAZ), which can damage, warp, burn, or discolor the surrounding area. This increased HAZ is undesirable, as post processing (cleaning) is then required, and furthermore, depending on the requirements and specifications of the material or product, significant heat build up can cause catastrophic failure of the part, its particular features, or simply render it unusable, for example with medical products that need clean, smooth features.

Picosecond Ultrafast Lasers

Pico lasers that produce less than 10 picoseconds pulses belong to the category of ultrafast lasers or ultrashort pulse lasers.  Ultrafast Lasers are ideal for the cold ablation of any material, including metals, ceramics, polymers, composites, coatings, glass, plastics, diamonds, and PET. Ultrafast lasers can even operate on layered substrates. Cold ablation allows for material to be removed without heating the residual matter. Thus, femtosecond fiber lasers will not produce heat affected zones (HAZ), splatter, or significant recast. Additionally, these ultrafast picosecond lasers will eliminate the need for any post-processing.

Picosecond vs Femtosecond Lasers:

In relation to femtosecond laser sources, picosecond lasers are typically more cost-effective, providing a higher average output power at a lower price point. Laser micromachining applications often benefit from that extremely high quality results provided by femtosecond pulses. However, short picosecond pulses often provide perfectly acceptably results when the processing parameters are optimal, making picosecond lasers the preferred choice, if you do not require the ultra-fine features and exceptional edge quality that femtosecond lasers provide.

LIDAR Becoming the Future of Bathymetry:

As in most LIDAR systems designed for distance measurement, bathymetric LIDAR relies on time-of-flight determination for calculating the distance to the target.  This is done by using a time-gated detector which is synchronized with a pulsed (typically picosecond or short-nanosecond range) laser source so that the round-trip time (Δt) can be determined.  In traditional LIDAR, the range (R) to the target is then determined using the following equation, R = C × Δt/2,  where C is the speed of light.  In bathymetry though there is an added complication because you want to determine the depth of the water, not the distance from the transceiver to the water.  Therefore, you need to measure both the distance to the surface of the water and the floor and take the difference between the two.  This is typically done using a “multi-beam” approach, which takes advantage of the difference in absorption of the water at various wavelengths.   As can be seen in the graph below, water has an absorption minima around 500 nm, meaning that green laser light will penetrate much deeper into the water than near-infrared light will.

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Want to Minimize Your LIDAR Footprint, Cost, and Energy Consumption?

Doppler LIDAR is growing in popularity, for instance, in wind farms, where the rapid detection of extreme weather changes can prevent damage to the wind turbine. Traditional anemometer/wind vane devices are too slow to report drastic weather changes in time to avoid damage. Alternatively, implementing a network of single-frequency Doppler LIDAR sensors around a wind farm, in conjunction with highly accurate wind models, allows for much higher accuracy wind speed readings and faster response times. This rapid access to accurate data provides time to adjust the blade angle to optimize the efficiency without overloading the turbine.

As we covered extensively in “Single-Frequency Fiber Lasers for Doppler LIDAR,” if you want to measure both the speed at which an object is moving and its location, there is no better option than frequency modulated (FM) LIDAR. For this signal processing methodology to work, you need to maintain precise control over the laser frequency. While a wide variety of single-frequency lasers have been used in Doppler LIDAR research, the industry as a whole has adopted picosecond and short-nanosecond pulsed, single-frequency fiber lasers as the ideal light source.

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Microchip Lasers: Fully Integrated Modules for LIDAR & 3D Scanning

LIDAR lasers are available in a vast range of configurations, tailored for different sets of end-use applications. The main determining factor for which type of LIDAR laser you need depends on whether your application is measuring a moving or stationary target. If your target is stationary, and distance is the only necessary measurement, short-pulsed lasers, with pulse durations of a few nanoseconds (even <1ns) and high pulse energy are what you’re looking for. This is also accurate for 3D scanning applications (given a stationary, albeit a much closer target), but select applications can also benefit from frequency-modulated, single-frequency (narrow-linewidth) fiber lasers. If your target is moving, and speed is the critical measurement, you need a single-frequency laser to ensure accurate measurement of the Doppler shift.

While the primary difference between traditional LIDAR and 3D scanning applications is the distance from the laser to the target, both sets of applications benefit from the features provided by high-quality microchip lasers. Lightweight and very compact modules, with low power draw, are perfect for integrating into portable devices for long battery life and increased mobility in the field. Excellent beam quality enables very small spot sizes and therefore, high peak power, incident upon the sample, for high-quality data collection. A simplistic design and low cost ensure a long lifetime of reliable performance, with reduced susceptibility to shock and vibration, without breaking your budget.

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Laser Induced Breakdown Spectroscopy (LIBS) in Biomedical Applications:

As the name implies LIBS utilizes a focused laser beam to breakdown or ablate the sample.  In this process, a microscopic portion of the sample is vaporized causing a momentary plasma to be formed.   This causes all of the ionized elements in the plasma plume to emit light corresponding to their unique atomic energy levels.  By collecting the light emitted from the induced plasma plume and directing into a spectrometer the measured lines can then be correlated with the presence and concentrations of the samples elemental structure.  While the physical process is quite different it is often helpful to think of LIBS, as an optical analog to mass spectrometry.

From this description above it should be obvious that the laser source used must have a sufficiently large energy density to ablate the sample in as short a time possible.  As a result, the vast majority of LIBS lasers are q-switched diode pumped solid state (DPSS) lasers, which typically provide millijoules of energy in a nanosecond to picosecond pulse duration.  When focused down to a small spot, this allows the laser to quickly ablate the sample, and trigger the spectrometer to immediately start the acquisition process to collect the atomic emissions from the short-lived plasma plume.

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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.

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Let Us Help

With 1000s of fielded units, and over 25 years of experience, providing researchers with the best laser solution for their application, our expert team is ready to help! Working with RPMC ensures you are getting trusted advice from our knowledgeable and technical staff on a wide range of laser products.  RPMC and our manufacturers are willing and able to provide custom solutions for your unique application.

If you have any questions, or if you would like some assistance please Contact Us here. Furthermore, you can email us at info@rpmclasers.com to talk to a knowledgeable Product Manager.

Alternatively, use the filters on this page to assist in narrowing down the selection of Picosecond lasers for sale. Finally, head to our Knowledge Center with our Lasers 101 page and Blogs, Whitepapers, and FAQ pages for further, in-depth reading.

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