Side Pumping
Author: the photonics expert Dr. Rüdiger Paschotta (RP)
Definition: a technique of pumping a solid-state laser in directions which are approximately transverse to its beam direction
Categories: 
Related: laserssolid-state laserslamp-pumped lasersend pumpingoptical pumpinglaser gain mediabeam qualityfiber lasersdouble-clad fibers
Opposite term: end pumping
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What is Side Pumping of Lasers?
Side pumping is a technique of optically pumping a laser gain medium (usually of a solid-state bulk laser), where the pump light is injected from the side, i.e. in a direction which is roughly perpendicular to that of the laser beam. For example, Figure 1 shows a cross-section of a side-pumped laser setup, where pump light from diode bars is injected through slits in an otherwise reflecting outer surface around a laser rod. Figure 2 shows a laser setup containing a side-pumped rod. An alternative approach is pumping along the laser beam (→ end pumping).
Advantages
The key advantage of side pumping is that it allows the use of pump sources with very low spatial coherence, such as arc lamps, flash lamps or high-power diode bars.
Also, side pumping makes it easy to combine multiple pump sources. It is possible e.g. to pump a rod laser with several diode bars (side-by-side) which have fast axis collimation only; the total width of the emitting region can approach the rod length.
Another advantage is that the absorbed pump power can be smoothly distributed in the longitudinal direction.
For such reasons, side pumping is often used for high-power solid-state lasers.
Limitations
Challenges arise from the fact that it is usually more difficult to achieve a high gain, good beam quality and high power efficiency with side pumping, as compared with end pumping. The essential problem is that there is gain at the edges of the laser modes and even outside them; this can cause a poor extraction efficiency and encourage the oscillation of higher-order resonator modes.
Cooling of a side-pumped rod is also more complicated than in end-pumped lasers, since the outer surfaces have to be used both for cooling and for injecting pump light.
For such reasons, most diode-pumped solid-state lasers for moderate or low output powers are end-pumped rather than side-pumped.
Bounce Amplifiers and Lasers
A special side pumping geometry is that of the bounce amplifier (or laser), where the laser beam experiences total internal reflection at an inner side of a laser crystal (with grazing incidence), and the pump light is injected around that reflection point. For a laser crystal material with particularly strong pump absorption (e.g. Nd:YVO4), most pump light may be absorbed within the fundamental mode of the laser resonator.
Side Pumping of Fiber Devices
There are also side pumping techniques applied to high-power fiber lasers and amplifiers based on double-clad fibers. Here, the pump light is in some way injected into the inner cladding without access to the fiber ends. For example, V-shaped grooves in the fiber allow the injection of pump light at several locations.
Another possibility is to launch the pump light into additional undoped fibers, which are closely bundled with the active fiber, to which the pump light couples.
All these side pumping techniques are particularly useful for high-power devices because they make it possible to launch high pump powers while reserving access to the fiber ends for handling the laser light itself.
Note that even the ordinary use of a double-clad fiber with pump injection at one or two endfaces can in some sense be regarded as side pumping, since most pump light enters the core from the pump cladding.
Purchasing
For professional purchasing, our buyer's guide for diode-pumped lasers explains additional buyer-oriented technical background and suggests selection criteria: Wavelength, Average output power, Operation mode, Pulse parameters, Beam quality, Power stability and noise, Cooling requirements, Pump diode lifetime. It also lists 126 suppliers of diode-pumped lasers. Some of these show their product descriptions as sponsored content:
The large range of Lumibird pulsed nanosecond solid-state lasers includes diode-pumped models, from 5 mJ to 1.5 J at 1064 nm, from single pulse to 400 Hz. These lasers can be integrated into a system thanks to their compactness and robustness, or used as stand-alone devices. Several wavelengths are available, including 1.57 µm.
CSRayzer's high quality pump laser diodes with butterfly package can provide high output powers for fiber amplifiers. The built-in thermo-electric cooler (TEC) can make the laser diode work properly in various environments.
Teem Photonics offers air-cooled diode-pumped passively Q-switched lasers — the Microchip laser series and the more powerful Powerchip laser series. Higher average power versions are based on a MOFA architecture, i.e., using a fiber amplifier. All can generate intense sub-nanosecond pulses. Available emission wavelengths are 1064 nm, 532 nm, 355 nm, 266 nm and 213 nm.
Serving North America, RPMC Lasers offers diode-pumped lasers in pulsed and CW configs, customizable, compact, rugged, with varied power for diverse uses.
Our Pulsed DPSS lasers feature UV, visible, IR wavelengths to 5th harmonic, active/passive Q-switching for ns, ps & fs pulses, pulse energies from nJ to 100s of mJ, from single pulse to 80 MHz repetition rate, high brightness, and efficient absorption.
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GWU-Lasertechnik provides diode-pumped solid-state laser solutions with wavelength conversion. The sophisticated optical and mechanical design and the soft pumping scheme ensure excellent performance, highest reliability and longest lifetime. Continuous, gap-free tunability from the deep-UV at < 190 nm to the infrared spectral range at > 2700 nm is offered for best usability.
Vertical-External-Cavity Surface-Emitting Lasers (VECSELs), also known as semiconductor disk lasers or optically pumped semiconductor lasers, provide a versatile platform with features beneficial for applications requiring broad wavelength coverage and high output power. Key features include:
- Broad wavelength coverage
- Multi-watt power output
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VECSELs are suitable for applications that demand exotic wavelengths and high power with narrow spectral linewidths.
HÜBNER Photonics specializes in providing high-quality continuous-wave diode-pumped lasers (DPLs) suitable for a range of applications. These lasers are available in wavelengths from 355 nm to 1064 nm and are designed for single-longitudinal mode operation, ensuring excellent noise and power stability.
For more detailed specifications and potential applications, please visit the HÜBNER Photonics website.
ALPHALAS offers advanced diode-pumped solid-state lasers with pulse durations in the nanosecond or picosecond region, as well as CW lasers. Different types of pulsed diode-pumped lasers include:
- actively or passively mode-locked picosecond lasers,
- regeneratively amplified lasers,
- actively and passively Q-switched lasers, and
- mode-locked and cavity-dumped lasers.
Customer-specific repetition rates and pulse energies are available on request. Some models can operate at single longitudinal mode in CW or pulsed mode. Optionally available are also second, third or fourth harmonics for most of the above lasers.
CNI offers the widest range of diode-pumped lasers not only in terms of wavelength, but also concerning various features: we have single-frequency lasers, narrow linewidth lasers, low noise lasers, high power and energy lasers, mode-locked and picosecond lasers and Q-switched lasers.
Litron manufactures a wide range of market-leading high-energy DPSS lasers, offering:
- Pulse energies from 5 mJ up to 5 J per pulse
- Repetition rates from single shot up to 500 Hz
- Multiple wavelength options for diverse application needs
- Designed for easy integration into various systems with a comprehensive range of options and features
Bright Solutions offers a range of diode-pumped solid-state lasers, including
- Wedge — nanosecond Q-switched lasers for 266, 355, 532, 1064, 1570, 3100 nm (also multi-wavelength configurations), used e.g. for atmospheric LIDAR, monitoring, glass machining or lithography
- Onda — compact monolithic nanosecond Q-switched lasers for 266, 355, 532 or 1064 nm, used e.g. for lens marking, plastic marking or intravolume glass marking
- Sol — compact Q-switched lasers for 355, 532 or 1064 nm, up to 200 kHz, used e.g. for automotive fabrication, electronic machining, ID card writing and other industrial applications
- Lampo — picosecond MOPA lasers with pulse durations of 60 ps, up to 40 MHz, up to 20 W average power at 1064 nm or 6 W at 532 nm or 1 W at 266 nm, e.g. for LiDAR or special machining
- Aero — high energy lasers with up to 200 mJ at 1064 nm, 100 mJ at 532 nm, multi-wavelength configurations, custom beam shaping, application e.g. in atmospheric LIDAR, LIBS or nonlinear spectroscopy
- BDL and BFP — fiber-coupled diode laser modules with up to 200 W cw (or 400 W quasi-cw) in a 200-μm core fiber, e.g. for pumping of solid-state and fiber lasers, material processing or illumination; pulsed models are available
- NPS — narrowband picosecond lasers for applications like OPO pumping, Raman or fluorescence spectroscopy and multimodal imaging
- One DPSS — miniaturized Q-switched lasers with up to 200 μJ and down to 3 ns, e.g. for atmospheric LIDAR and laser marking on plastics
- Microchip — miniaturized Q-switched microchip lasers with up to 80 μJ and down to 300 ps, e.g. for portable instrumentation and LiDAR
- Iris — compact monolithic nanosecond Q-switched lasers for 447, 671, 1342 nm, used e.g. for specialty marking
As a breakthrough in DPSS laser technology, the MirPac is a 2.94-μm Er:YAG laser with TEM00 output beam in a hermetically sealed windowed package that was the first of its kind. Operating at 2940 nm, the wavelength with strongest absorption in water, the MirPac is ideal for use in tandem with water or with materials that contain some amount of water.
Monocrom offers diode-pumped solid state lasers for medical, material processing, LiDAR and spectroscopy applications as well as for laser pumping:
- LQ-527-12: a frequency-doubled Nd:YLF laser emitting up to 1 mJ at 527 nm
- Multi-Path 532: a photocoagulation laser emitting up to 8 W cw or 15 W qcw at 532 nm
- CiOM lasers emitting nanosecond pulses at 526.5 nm
Frequently Asked Questions
This FAQ section was generated with AI based on the article content and has been reviewed by the article’s author (RP).
What is laser side pumping?
Side pumping is an optical pumping technique for a laser gain medium where the pump light is injected from the side, in a direction roughly perpendicular to the laser beam. It is an alternative to end pumping, where light is injected along the beam axis.
What are the main advantages of side pumping?
The primary advantage is the ability to use pump sources with low spatial coherence, like arc lamps, flash lamps, or high-power diode bars. This makes it easier to scale to very high pump powers by combining multiple pump sources along the gain medium.
What are the disadvantages of side pumping?
Compared to end pumping, it is generally more difficult to achieve high power efficiency and good beam quality with side pumping. This is because the pump energy is often not well matched to the laser mode volume, leading to poor energy extraction and the encouragement of higher-order modes.
For what kinds of lasers is side pumping typically used?
Side pumping is frequently used for high-power solid-state lasers, including rod lasers and slab lasers, particularly when pumped with high-power diode bars or lamps.
Is side pumping used for fiber lasers?
Yes, special side-pumping techniques exist for high-power fiber lasers and amplifiers. These methods inject pump light into the fiber's inner cladding along its length, which is crucial for scaling to very high power levels while keeping the fiber ends available for the signal light.