Q-switching active

Until recently a general drawback of this passive Q-switching scheme was the difficulty of obtaining an exact synchronization of the giant pulse with other events in more complex experiments. This difficulty does not exist with active Q-switching in which an electro-optic device, e.g. a Kerr-cell or Pockels-cell, is used instead of a dye cell, and one is able to determine exactly the time at which... 

There is another way to obtain giant laser pulses of a few ns duration, known as active Q-switching. The shutter is an electro-optical cell which is triggered at some preset time after the pump flash. These electro-optical shutters are Kerr cells or Pockels cells. 

Active Q-switching occurs when laser light access to one of the mirrors in the cavity is controlled electro-optical cell, which works on the principle of affecting the passage of polarized light (see... 

Li P, Wang QP, Zhang XY, Wang YR, Chen XH (2010) Compact and efficient diode-pumped actively Q-switched 1319 nm Nd YAG ceramic laser. Laser Phys 20 1603-1607... 

Task (a) is addressed by multiple acquisition and co-addition of solid echoes according to the sequence of Ostroff and Waugh . Fast repetition of pulses in the OW4 sequence leads to an effective slowing down of the apparent transverse relaxation (spin locking in a quasi steady state) such that the gain is over-proportional. Combined with an active Q-switch for dead time reduction, a number of echoes (up to 20) could be detected for averaging. 

Picosecond transient absorption was monitored on a spectrometer consisting of two dye lasers synchronously pumped by an actively mode-locked, actively Q-switched Nd-YAG laser (JK-AML 2000). Single pulses... 

The incorporation of Cr" + ions in crystals is presently an active research subject, due to the possibility of realizing new broadly tunable solid state lasers in the infrared, which will operate at room temperature. Moreover, the spectroscopic properties of this ion are particularly useful in the development of saturable absorbers for Q-switching passive devices. At the present time, Cr + YAG is the most common material employed as a passive Q-switch in Nd YAG lasers. This is because the ions provide an adequate absorption cross section at the Nd + laser wavelength (1.06 /um), together with the good chemical, thermal, and mechanical properties of YAG crystals, which are required for stable operation. 

The second category comprises the flash photolysis experiments using the short high power light pulses from Q-switched lasers, furthermore all investigations of time-dependent behavior of excited dye molecules, which play an important role as active material in dye lasers or as saturable absorbers in passive Q-switched giant pulse lasers. 

Fig. 7. Experimental arrangement of a giant-pulse laser (Q-switching by dye solution). AM, active material (e.g. ruby crystal rod), F, flashlamp, Mj, 2, resonator mirrors, DC, dye cell...

This technique is known as the passive Q-switch. The dye acts as an absorber for weak light, so that the population of excited atoms or molecules in the active material can increase until its maximum level is reached. The dye cell is in fact a high-speed shutter. 

Q-switched laser A laser in which the state of the device introducing important losses in the resonant cavity and preventing lasing operation is suddenly switched to a state where the device introduces very low losses. This increases rapidly the Quality factor of the cavity, allowing the build-up of a short and very intense laser pulse. Typical pulse durations are in the ns range. The Q-switching may be active (a rotating mirror or electro-optic device) or passive (a saturable absorber). 

Fig. 12.13 The inset of (a) shows the scheme of a very compact all solid-state laser using the organic semiconductor film as active medium. The pump source is a commercially available diode-pumped, Q-switched, frequency-tripled Nd YAG-microchip laser (Uniphase NanoUV-355). The organic semiconductor laser can be placed directly in front of the pump laser. Thus the total length of this very compact solid-state...

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