What is passive mode locking?

Passive mode-locking techniques are those that do not require a signal external to the laser (such as the driving signal of a modulator) to produce pulses. Rather, they use the light in the cavity to cause a change in some intracavity element, which will then itself produce a change in the intracavity light.

What is active mode locking?

Active mode locking involves the periodic modulation of the resonator losses or of the round-trip phase change, achieved e.g. with an acousto-optic or electro-optic modulator, a Mach–Zehnder integrated-optic modulator, or a semiconductor electroabsorption modulator.

What is saturable drug absorption?

The drug then passes through the portal vein to the liver and then into the systemic circulation. If any of these processes becomes saturated, then increases in the administered dose will not correspond to increases in amount of drug absorbed into the body. This is called saturable drug absorption.

What is reverse saturable absorption?

Reverse saturable absorption. A class of nonlinear absorbers in which the excited state absorption is large compared to the ground state absorption can undergo a process called reverse saturable absorption (RSA), also known as reversible saturable absorption.

What is the advantage of mode locking?

Advantages of fundamental mode locking are that possible instabilities of harmonic mode locking are avoided, and that the laser setup is usually more compact. On the other hand, harmonically mode-locked lasers have a potential for lower laser noise.

Why is mode locking essential?

Mode locking is the most important technique for generating pulses with picosecond and femtosecond durations. Each time the pulse hits the output coupler mirror, a part of its energy is emitted, so the laser output is a regular pulse train. The gain medium replenishes the pulse energy in each roundtrip.

What does saturable drug mean?

Drug absorption is the process by which a drug molecule moves from the site of administration to the systemic circulation. Following intravenous administration, there is no absorption process since the drug is directly introduced into the blood stream. This is called saturable drug absorption.

What is reverse absorption?

What is difference between Q-switching and mode locking?

Dear Xinyang, passive Q-switching takes place in both cases as in time of “giant” pulse generation so in time of mode locking. Mode locking needs the saturated absorber with relaxation time less then round trip time in the given cavity while the giant pulse generation develops better with slow relaxing absorber.

Are there saturable absorbers for passive mode locking?

These are also suitable for passive Q switching, particularly at lower pulse energies. Other semiconductor saturable absorbers for mode locking or Q switching are based on quantum dots e.g. of lead sulfide (PbS) suspended in glasses [9].

What’s the difference between a fast and slow saturable absorber?

When dealing with pulses, a fast saturable absorber is one with a recovery time well below the pulse duration, whereas a slow absorber is one with a recovery time well above the pulse duration. This means that the same device may be either a fast absorber or a slow absorber, depending on the pulses with which it is used.

What is the saturation parameter of a slow saturable absorber?

The saturation parameter of a slow saturable absorber (e.g. in a mode-locked laser) is the ratio of the incident pulse fluence to the saturation fluence of the device. For a fast absorber, it is the pulse peak intensity divided by the saturation intensity.

What are the requirements for a saturable absorber for a Q switching laser?

Typical requirements on a saturable absorber for a passively Q-switched laser are: The total non-saturated absorption must be relatively high – often slightly smaller than the small-signal gain of the laser medium, if a high pulse energy and short pulse duration is desired.