Tunable lasers handbook phần 5 pptx

184 F. J. Duarte

a

b

Coaxial flashlamp dye laser

FIGURE 8

(Reprinted with permission from Duarte et a/. [72] and Elsevier Science.)

Schematics of (a) flashlamp-pumped MPL oscillator and (b) HMPGI oscillator.

In this regard, the narrow-linewidth emission pulse must be synchronized to

arrive during the buildup period of the forced-oscillator pulse. In the case of

forced oscillators using unstable resonator optics, the magnification of the optics

must be optimized relative to the beam dimensions of the master oscillator to

completely fill the active volume of the forced oscillator. Also. the injection beam

should be aligned exactly for concentric propagation along the optical axis of

the forced oscillator. The performance of flashlamp-pumped master-oscillator/

forced-oscillator systems is listed in Table 10. In addition to those results, energy

gains as high as 478 have been reported for an MPL master oscillator and a

forced oscillator with a magnification factor of 5 [62].

The use of cw dye laser oscillators as injection sources of amplification

stages utilizing ring cavity configurations is discussed by Blit et al. [78] and Tre￾hin et a/. [79].

4. cw LASER-PUMPED DYE LASERS

The cw dye lasers span the spectrum from -370 to -1000 nm. Frequency

doubling extends their emission range into the 260- to 390-nm region. An impor￾tant feature of cw dye lasers has been their ability to yield extremely stable

emissions and very narrow linewidths. These qualities have made cw dye lasers

5 Dye Lasers 185

FIGURE 9

sion from Duarte et al. [72] and Elsevier Science.)

Partial view of ruggedized multiple-prism grating oscillator. (Reprinted with permis￾Master

oscillator

Forced

oscillator

Grating

FIGURE 1 0 Master-oscillator/forced-oscillator system. (Reprinted with permission from

Duarte and Conrad 1731.)

extremely important to applications in physics, spectroscopy, and other sciences.

A thorough and extensive description of this branch of dye lasers is given by

Hollberg [3]. Here some of the most important features of cw dye lasers and

their emission characteristics are surveyed.

4.1 Excitation Sources for cw Dye Lasers

The main sources of excitation for cw dye lasers are the argon ion (AI-+) and

the krypton ion (Kr+) lasers. These are conventional discharge lasers that emit

186 F.J. Duarte

TABLE 8

Master Oscillatora

Optimum Performance of Ruggedized Multiple-Prism Grating

Output energy (mJ) A\’ (hIHz) 6%’h AB (mrad) C (rnkl)

2.2-3.6 300 4.63 x 10-7 0.35 0.01

aFrom Duarte er al. [72], with permission.

TABLE 9 Performance of Ruggedized Multiple-Prism Grating Master

Oscillator Prior (First Row) and Following (Second Row) Field Testa

Output energy (mJ) Av (MHz) 6k% AB (mrad) C (mhl)

2-3

2-3

300 1.45 x 10-6 0.51 0.01

300 1.18 x 10-6 0.45 0.01

.From Duarte et al. [72]. with permission

TABLE 1 0

Forced-Oscillator Systems0

Performance of Flashlamp-Pumped Master-Oscillator/

Forced-oscillator output

blaster oscillator configuration energy Energy gain Reference

Tso etalons Flat-mirror cavity 600 mJ at 589 nm 200 [751

Three etalons Planoconcave resonaior 3J -267 [761

Trio etalons Flat-mirror cavity 300 mJ at 590 nm [771

A\, = 8.65 GHz

i2v = 4 GH2

A\’ = 346 MHz

MPL Positive-branch unstable resonator 600 mJ at 590 nm 60 ~731

Av 5 175 MHz

OXdapted from Duarte [37]. with permission.

via excitation mechanisms such as Penning ionization [go]. Table 11 lists some

of the most widely used transitions in dye laser excitation. Note that the quoted

powers are representative of devices available commercially. It should also be

indicated that not all transitions may be available simultaneously and that more

than one set of mirrors may be required to achieve lasing in different regions of

the spectrum. Also, for a mirror set covering a given spectral region, lasing of

individual lines may be accomplished using intracavity prism tuners.

5 Dye Lasers 187

TABLE 1 1 Excitation Lasers of cw Dye Lasers

Laser Transitiona Wavelength (nm) Powerb (W)

5p4p;. - .5s2P,,,

5p4P9: - 5s4Px,i

5p4PQ1 - 5S4P,,>

.5p4Do, - 5S2P,,?

528.69

514.53

501.72

496.51

487.99

476.49

472.69

465.79

457.93

4.54.50

799.32

752.55

676.4

647.09

568.19

530.87

520.83

1.5

10.0

1 .s

2.5

7.0

2.8

1.2

0.75

1.4

1 .o

0.1

0.35

0.2

1.4

0.53

0.7

0.25

~~~~~~~~ ~~~~ ~ ~ ~

OTransition identification from [SO].

hAr+ laser power from [3] and Kr+ laser powers from [81]

Given the relatively long cavity length of these lasers (typically -1 m), and

their narrow beamwaists (-1 mm), the output beam characteristics are excellent.

In this regard these 1a.sers can offer single-transverse-mode outputs and beam

divergence’s approaching the diffraction limit.

In addition to the output powers listed in Table 11, higher powers are avail￾able. For instance, Baving et al. [82] reports the use of a 200-W multiwave￾length A@ laser in the excitation of a linear cw dye laser. The Ar+ laser oscillated

simultaneously at 457.93, 476.49,487.99,496.51, 501.72, and 514.53 nm. Other

lasers useful in the excitation of cw dye lasers include HeNe [83,84], frequency￾doubled cw Nd:YAG [3], and semiconductor lasers.

4.2 cw Dye Laser Cavities

The cw dye laser cavities evolved from the simple and compact linear cavity

first demonstrated by Peterson et al. [85]. External mirrors and intracavity tuning

prisms were introduced by Hercher and Pike [86] and Tuccio and Strome [25]

(Fig. 11). An important innovation in cw dye lasers was the introduction of the

dye jet [83]. Fast flow of the dye solution at speeds of a few m-s-1 is important

188 F. J. Duarte

Stainless

Brewster

Angle Prism

Argon Laser Beam

514.5 nm

Dye Laser

Beam

FIGURE 1 1

and Strome [XI.)

Linear cw dye laser cavity configuration. (Reprinted 41th permission from Tuccio

to induce heat dissipation and hence reduce thermally induced optical inhomo￾geneities in the active medium [85].

Widely used configurations of cur dye laser cavities include the three-mirror

folded linear cavity (see, for example, [20] and references therein) and ring-dye

laser cavities (see, for example, [3] and references therein). These two configura￾tions are shown in Fig. 12. In both cases excitation from a cw laser is accom￾plished semilongitudinally to the optical axis defined by M, and M,. Tuning ele￾ments. or frequency-selective elements (FSEs), are deployed between h/I, and

M, in the linear cavity, and between M, and M, in the ring cavity. The unidirec￾tional device (UDD) depicted in Fig. 12(b) is an optical diode that controls the

direction of propagation in the ring cavity [3].

Ring-dye laser cavities circumvent the problem of spatial hole burning associ￾ated with linear cavities [3]. Also ring cavities are reported to yield higher single￾longitudinal-mode power than linear cavities [3]. However, linear configurations

offer greater optical simplicity and lower oscillation thresholds.

Diels [87] discusses the use of propagation matrices, applicable for Gauss￾ian beam propagation analysis, to characterize stability conditions and astigma￾tism in cw dye laser cavities.

Linewidth narrowing and FSEs used in cw dye lasers are birefringent crys￾tals. prisms, gratings, and Fabry-Perot etalons. Often two or more FSEs are nec￾essary to achieve single-longitudinal-mode oscillation. The first stage in the fre￾quency narrowing usually consists of utilizing prisms or birefringement filters to

yield a bandwidth compatible with the free spectral range (FSR) of the first of

two etalons. In turn, the second etalon has a FSR and finesse necessary to restrict

oscillation in the cavity to a single-longitudinal mode [3]. Alternative approaches

may replace the second etalon by an interferometer [88]. The performance of var￾ious linear and ring cw dye lasers is listed in Table 12.