255:, the cavity end mirrors are 100% reflective, so that no output beam is produced when the Q is high. Instead, the Q-switch is used to "dump" the beam out of the cavity after a time delay. The cavity Q goes from low to high to start the laser buildup, and then goes from high to low to "dump" the beam from the cavity all at once. This produces a shorter output pulse than regular Q-switching. Electro-optic modulators are normally used for this, since they can easily be made to function as a near-perfect beam "switch" to couple the beam out of the cavity. The modulator that dumps the beam may be the same modulator that Q-switches the cavity, or a second (possibly identical) modulator. A dumped cavity is more complicated to align than simple Q-switching, and may need a
187:. The reduction of losses (increase of Q) is triggered by an external event, typically an electrical signal. The pulse repetition rate can therefore be externally controlled. Modulators generally allow a faster transition from low to high Q, and provide better control. An additional advantage of modulators is that the rejected light may be coupled out of the cavity and can be used for something else. Alternatively, when the modulator is in its low-Q state, an externally generated beam can be coupled
233:
1085:
340:
349:
220:
Ideally, this brings the absorber into a state with low losses to allow efficient extraction of the stored energy by the laser pulse. After the pulse, the absorber recovers to its high-loss state before the gain recovers, so that the next pulse is delayed until the energy in the gain medium is fully replenished. The pulse repetition rate can only indirectly be controlled, e.g. by varying the laser's
380:
for different coloured inks. Nd:YAG lasers are currently the most favoured lasers due to their high peak powers, high repetition rates and relatively low costs. In 2013 a picosecond laser was introduced based on clinical research which appears to show better clearance with difficult-to-remove colours
146:
by stimulated emission to begin. Because of the large amount of energy already stored in the gain medium, the intensity of light in the laser resonator builds up very quickly; this also causes the energy stored in the medium to be depleted almost as quickly. The net result is a short pulse of light
279:
duration. Even when the average power is well below 1 W, the peak power can be many kilowatts. Large-scale laser systems can produce Q-switched pulses with energies of many joules and peak powers in the gigawatt region. On the other hand, passively Q-switched microchip lasers (with very short
219:
device. Initially, the loss of the absorber is high, but still low enough to permit some lasing once a large amount of energy is stored in the gain medium. As the laser power increases, it saturates the absorber, i.e., rapidly reduces the resonator loss, so that the power can increase even faster.
266:
is placed inside a Q-switched cavity. Pulses of light from another laser (the "master oscillator") are injected into the cavity by lowering the Q to allow the pulse to enter and then increasing the Q to confine the pulse to the cavity where it can be amplified by repeated passes through the gain
162:
Here, the Q-switch is an externally controlled variable attenuator. This may be a mechanical device such as a shutter, chopper wheel, or spinning mirror/prism placed inside the cavity, or (more commonly) it may be some form of
50:, another technique for pulse generation with lasers, Q-switching leads to much lower pulse repetition rates, much higher pulse energies, and much longer pulse durations. The two techniques are sometimes applied together.
247:
can be reduced by not reducing the Q by as much, so that a small amount of light can still circulate in the cavity. This provides a "seed" of light that can aid in the buildup of the next Q-switched pulse.
224:
power and the amount of saturable absorber in the cavity. Direct control of the repetition rate can be achieved by using a pulsed pump source as well as passive Q-switching.
111:. A high Q factor corresponds to low resonator losses per roundtrip, and vice versa. The variable attenuator is commonly called a "Q-switch", when used for this purpose.
195:
or wavelength). When the Q is raised, lasing builds up from the initial seed, producing a Q-switched pulse that has characteristics inherited from the seed.
317:
376:. Full removal can take between six and twenty treatments depending on the amount and colour of ink, spaced at least a month apart, using different
316:) by measuring the time it takes for the pulse to get to some target and the reflected light to get back to the sender. It can be also used in
207:, a material whose transmission increases when the intensity of light exceeds some threshold. The material may be an ion-doped crystal like
240:-based design. Bottom: The Pockel's cell-based design needs thin film polarizers. The direction of the emitted pulse depends on the timing.
275:
A typical Q-switched laser (e.g. a Nd:YAG laser) with a resonator length of e.g. 10 cm can produce light pulses of several tens of
1045:
381:
such as green and light blue. Q-switched lasers can also be used to remove dark spots and fix other skin pigmentation issues.
191:
the cavity through the modulator. This can be used to "seed" the cavity with a beam that has desired characteristics (such as
565:
532:
280:
resonators) have generated pulses with durations far below one nanosecond and pulse repetition rates from hundreds of
34:
can be made to produce a pulsed output beam. The technique allows the production of light pulses with extremely high (
462:
430:
138:
and other processes, after a certain time the stored energy will reach some maximum level; the medium is said to be
784:
142:. At this point, the Q-switch device is quickly changed from low to high Q, allowing feedback and the process of
954:
420:
675:
Reiner, J. E.; Robertson, J. W. F.; Burden, D. L.; Burden, L. K.; Balijepalli, A.; Kasianowicz, J. J. (2013).
97:
does not return, and lasing cannot begin. This attenuation inside the cavity corresponds to a decrease in the
312:. However, Q-switched lasers can also be used for measurement purposes, such as for distance measurements (
58:
1010:
126:, but laser operation cannot yet occur since there is no feedback from the resonator. Since the rate of
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352:
57:, and independently discovered and demonstrated in 1961 or 1962 by R.W. Hellwarth and F.J. McClung at
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360:
176:
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often takes advantage of the high peak powers of these lasers, offering applications such as
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of light into the gain medium (producing an optical resonator with low Q). This produces a
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DeMaria, A. J.; Stetser, D. A.; Glenn, W. H. (1967-06-23). "Ultrashort Light Pulses".
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stored in the gain medium increases as the medium is pumped. Due to losses from
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McClung, F.J.; Hellwarth, R.W. (1962). "Giant optical pulsations from ruby".
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medium. The pulse is then allowed to leave the cavity via another Q switch.
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by shattering ink pigments into particles that are cleared by the body's
292:
Q-switched lasers are often used in applications which demand high laser
236:
Regenerative amplifier. Red line: Laser beam. Red box: Gain medium. Top:
232:
74:
47:
919:
455:
LASER: The inventor, the Nobel laureate, and the thirty-year patent war
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297:
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is dependent on the amount of light entering the medium, the amount of
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184:
164:
69:. Optical nonlinearities such as Q-switching were fully explained by
62:
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to choose the best time at which to dump the beam from the cavity.
119:
99:
35:
276:
640:
Treacy, E.B. (1968). "Compression of picosecond light pulses".
548:
Bloembergen, Nicolaas (2011). "The Birth of
Nonlinear Optics".
369:
244:
208:
131:
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281:
93:. When the attenuator is functioning, light which leaves the
31:
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85:
Q-switching is achieved by putting some type of variable
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in nanosecond pulses, such as metal cutting or pulsed
547:
580:
1101:
478:
422:Optical Pulses - Lasers - Measuring Techniques
778:
677:"Temperature Sculpting in Yoctoliter Volumes"
151:, which may have a very high peak intensity.
725:
541:
80:
785:
771:
412:
368:Q-switched lasers are also used to remove
53:Q-switching was first proposed in 1958 by
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154:There are two main types of Q-switching:
681:Journal of the American Chemical Society
574:
472:
231:
1046:Multiple-prism grating laser oscillator
633:
509:
418:
1102:
639:
452:
270:
198:
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118:while the Q-switch is set to prevent
46:(constant output) mode. Compared to
446:
211:, which is used for Q-switching of
13:
457:. New York: Simon & Schuster.
262:In regenerative amplification, an
147:output from the laser, known as a
14:
1121:
215:, a bleachable dye, or a passive
1084:
1083:
347:
338:
203:In this case, the Q-switch is a
425:. Academic Press. p. 192.
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955:Amplified spontaneous emission
668:
519:. Springer Biographies. 2018.
114:Initially the laser medium is
1:
603:10.1126/science.156.3782.1557
419:FrĂĽngel, Frank B. A. (2014).
406:
662:10.1016/0375-9601(68)90584-7
61:using electrically switched
59:Hughes Research Laboratories
30:, is a technique by which a
7:
1011:Chirped pulse amplification
384:
284:to several megahertz (MHz)
227:
179:device – a
10:
1126:
815:List of laser applications
792:
482:Journal of Applied Physics
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993:
940:
828:
800:
746:Science History Institute
525:10.1007/978-3-319-61940-8
361:Science History Institute
346:
337:
332:
81:Principle of Q-switching
306:3D optical data storage
77:in 1981 for this work.
16:Laser pulsing technique
805:List of laser articles
732:Klett, Joseph (2018).
241:
558:10.1364/nlo.2011.nwa2
453:Taylor, Nick (2000).
359:Podcast Episode 220,
235:
144:optical amplification
24:giant pulse formation
22:, sometimes known as
980:Population inversion
173:magneto-optic effect
136:spontaneous emission
124:population inversion
71:Nicolaas Bloembergen
1031:Laser beam profiler
950:Active laser medium
890:Free-electron laser
810:List of laser types
654:1968PhLA...28...34T
595:1967Sci...156.1557D
589:(3782): 1557–1568.
495:1962JAP....33..828M
310:3D microfabrication
271:Typical performance
199:Passive Q-switching
128:stimulated emission
89:inside the laser's
517:The Laser Inventor
391:Laser construction
242:
205:saturable absorber
158:Active Q-switching
1097:
1096:
1051:Optical amplifier
900:Solid-state laser
693:10.1021/ja309892e
642:Physics Letters A
567:978-1-55752-915-2
534:978-3-319-61939-2
503:10.1063/1.1777174
366:
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264:optical amplifier
109:optical resonator
91:optical resonator
1117:
1087:
1086:
1061:Optical isolator
1026:Injection seeder
1006:Beam homogenizer
985:Ultrashort pulse
975:Lasing threshold
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734:"Second Chances"
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687:(8): 3087–3094.
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550:Nonlinear Optics
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401:Injection seeder
374:lymphatic system
353:“Rethinking Ink”
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322:temperature jump
318:chemical dynamic
302:Nonlinear optics
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960:Continuous wave
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1016:Gain-switching
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489:(3): 828–829.
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140:gain saturated
105:quality factor
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73:, who won the
65:shutters in a
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1001:Beam expander
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217:semiconductor
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213:Nd:YAG lasers
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177:electro-optic
175:device or an
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1041:Mode locking
994:Laser optics
750:. Retrieved
741:
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648:(1): 34–35.
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436:. Retrieved
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320:study, e.g.
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288:Applications
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257:control loop
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181:Pockels cell
161:
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104:
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55:Gordon Gould
52:
27:
23:
19:
18:
1071:Q-switching
932:X-ray laser
925:Ti-sapphire
895:Laser diode
873:Helium–neon
378:wavelengths
294:intensities
277:nanoseconds
167:such as an
149:giant pulse
95:gain medium
75:Nobel prize
48:modelocking
20:Q-switching
438:1 February
407:References
325:relaxation
298:holography
171:device, a
87:attenuator
67:ruby laser
28:Q-spoiling
1036:M squared
858:Gas laser
841:Dye laser
701:0002-7863
611:0036-8075
185:Kerr cell
165:modulator
63:Kerr cell
1104:Category
1089:Category
883:Nitrogen
752:June 27,
719:23347384
627:27074052
619:17797635
552:: NWA2.
385:See also
228:Variants
120:feedback
100:Q factor
36:gigawatt
868:Excimer
748:: 12–23
710:3892765
650:Bibcode
591:Bibcode
583:Science
491:Bibcode
370:tattoos
327:study.
107:of the
38:) peak
910:Nd:YAG
905:Er:YAG
846:Bubble
794:Lasers
717:
707:
699:
625:
617:
609:
564:
531:
469:p. 93.
461:
429:
245:Jitter
209:Cr:YAG
132:energy
116:pumped
915:Raman
744:(1).
623:S2CID
282:hertz
251:With
40:power
32:laser
920:Ruby
754:2018
715:PMID
697:ISSN
615:PMID
607:ISSN
562:ISBN
529:ISBN
459:ISBN
440:2015
427:ISBN
308:and
222:pump
189:into
878:Ion
705:PMC
689:doi
685:135
658:doi
599:doi
587:156
554:doi
521:doi
499:doi
238:AOM
183:or
103:or
26:or
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