Master Oscillator (MO)

The master oscillator is the heart of the MOPA system. It generates a low-power seed signal that is tailored to achieve the performance of the MOPA system required by the application. Depending on the application the characteristics of the "seed" signal are optimized for specific wavelengths, linewidths, or pulse durations.

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Power Amplifier (PA)

The power amplifier boosts the seed signal to high power and energy levels to meet the demands of applications such as throughput or material removal rates. There are several design options for the power amplifier stage to meet the widely varying demands of applications in industrial, scientific, or medical applications. For instance, bulk amplifiers are well suited to generate high-energy pulses. While fiber-based amplifiers are limited in energy they are well suited to generate high power levels. It is common to combine multiple amplifier stages to reach the required performance. 

MOPA Advantages

High Power and Energy levels: Laser powers and energy levels can be scaled over several orders of magnitude by selecting and combining the appropriate power amplifier stages. 

Superb Beam Quality: The oscillators pristine beam quality is maintained in the amplifier stage enabling excellent surface quality and clean cuts, precise welds, accurate measurements, and pristine images.

Spectral Purity: The amplified laser maintains the MO's narrow linewidth and stable wavelength, crucial for applications like spectroscopy and optical communications.

Versatility: Tailor different MO and PA combinations to meet specific needs, from ultra-short pulses to continuous wave (CW) operations, tuning of the wavelength, modulation of the power or energy levels, or pulse picking. 

MOPA Applications

Material Processing: Enables precise cutting, drilling, and welding.

LIDAR: Facilitates accurate 3D environmental mapping.

Pumping other Lasers: Enhances other laser systems' capabilities.

Medical Imaging: Generates high-power, ultra-fast pulses for advanced imaging, diagnostics and therapies.

Empowering Innovation with MOPA 

MOPA systems, at the forefront of laser technology, offer unparalleled power, quality, and versatility. Integral in driving advancements across various sectors, they provide precision where it matters most.

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Master Oscillator Power Amplifier

Author: the photonics expert Dr. Rüdiger Paschotta

The term master oscillator power amplifier (MOPA) refers to a configuration consisting of a master laser (or seed laser) and an optical amplifier to boost the output power. A special case is the master oscillator fiber amplifier (MOFA), where the power amplifier is a fiber device. In other cases, a MOPA may consist of a solid-state bulk laser and a bulk amplifier, or of a tunable external-cavity diode laser and semiconductor optical amplifier.

Although a MOPA configuration is in principle more complex than a laser which directly produces the required output power, the MOPA concept can have certain advantages:

• With a MOPA instead of a simple laser oscillator, it can be easier to reach the required performance e.g. in terms of linewidth, wavelength tuning range, beam quality or pulse duration if the required power is very high. This is because various performance aspects are decoupled from the generation of high powers. This gives extra flexibility, e.g. when a gain-switched laser diode (&#; picosecond diode lasers) is used as a seed laser. Note also that it can be advantageous to avoid the presence of additional optical components such as wavelength tuning elements in a high-power laser resonator; with a MOPA architecture, one can place these in the oscillator, where they do not have to withstand high optical intensities, do not spoil the power efficiency, etc.
• The same aspects apply to other kinds of modulation, e.g. intensity or phase modulation: it may be advantageous to modulate the low-power seed laser, or to use an optical modulator between seed laser and power amplifier, rather than to modulate a high-power device directly. Slower power modulation may be done by adjusting the amplifier's pump power, without significantly affecting e.g. the obtained pulse duration or wavelength.
• The combination of an existing laser with an existing amplifier (or an amplifier chain) may be simpler than developing a new laser with higher output power.
• The optical intensities are lower in an amplifier, compared with the intracavity intensities in a laser.

However, the MOPA approach can also have disadvantages:

• The complexity of the setup is higher.
• The wall-plug efficiency is often lower. However, it may also be higher, e.g. if that approach allows to remove lossy optical elements from the high-power stage.
• The resulting laser noise tends to be higher, since an amplified source can not reach the shot noise level (&#; amplifier noise). Effects of drifts of the seed power may be suppressed, however, if the amplifier is operated in a strongly saturated regime.
• A MOPA can be highly sensitive to back-reflections, which are amplified again before entering the master laser. This feedback sensitivity can often be cured only by placing a Faraday isolator behind the amplifier. Particularly for high-power pulsed devices, this can introduce serious limitations.

MOPA architectures are also used for pulsed laser sources. In that case, the amplifier may be used as a reservoir of energy. If a pulse from the seed laser extracts a significant fraction of the stored energy, the effect of gain saturation is relevant: the amplifier gain drops during the pulse. This can lead to a deformation of the temporal pulse shape. In some cases, the pulse shape from the seed source is tailored so as to obtain the desired pulse shape after amplification.

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