Experimental investigation about influences of longitudinal-mode structure of pumping source on a Ti:sapphire laser

Transcription

1 Experiental investigation about influences of longitudinal-ode structure of puping source on a Ti:sapphire laser Huadong Lu, Jing Su,* Changde Xie, and Kunchi Peng State Key Laboratory of Quantu Optics and Quantu Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan, Shanxi , China * jingsu@sxu.edu.cn Abstract: Using a ulti-longitudinal-ode (MLM) and a singlelongitudinal-ode (SLM) all-solid-state green lasers to be the puping sources of a continuous-wave Ti:sapphire laser, respectively, the intensitynoise dependence of the Ti:sapphire laser on the longitudinal-ode structure of puping sources is experientally studied. The coparison between the theoretical prediction based on the quantu-echanical odel and the experiental easureent for the intensity-noise spectra is presented. 011 Optical Society of Aerica OCIS codes: (70.500) Fluctuations, relaxations, and noise; ( ) Lasers, frequency doubled; ( ) Lasers, ring; ( ) Lasers, titaniu. References and links 1. P. F. Moulton, Spectroscopic and laser characteristics of Ti:Al O 3, J. Opt. Soc. A. B 3(1), (1986).. S. Qaar, H. Xiong, and M. S. Zubairy, Influence of pup-phase fluctuations on entangleent generation using a correlated spontaneous-eission laser, Phys. Rev. A 75(6), (007). 3. D. Wang, Y. Shang, Z. Yan, W. Wang, X. Jia, C. Xie, and K. Peng, Experiental investigation about the influence of pup phase noise on phase-correlation of output optical fields fro a non-degenerate paraetric oscillator, Europhys. Lett. 8(), 4003 (008). 4. D. Wang, Y. Shang, X. Jia, C. Xie, and K. Peng, Dependence of quantu correlations of twin beas on the pup finesse of an optical paraetric oscillator, J. Phys. At. Mol. Opt. Phys. 41(3), (008). 5. T. C. Ralph, C. C. Harb, and H. A. Bachor, Intensity noise of injection-locked lasers: Quantu theory using a linearized input-output ethod, Phys. Rev. A 54(5), (1996). 6. C. C. Harb, T. C. Ralph, E. H. Huntington, D. E. McClelland, H.-A. Bachor, and I. Freitag, Intensity-noise dependence of Nd:YAG lasers on their diode-laser pup source, J. Opt. Soc. A. B 14(11), (1997). 7. Z. Jing, Z. Kuanshou, C. Yanli, Z. Tiancai, X. Changde, and P. Kunchi, Intensity noise properties of LD puped single-frequency ring laser, Acta Opt. Sin. 0(10), (000). 8.. Zhang, Y. Cheng, T. Zhang, K. Zhang, C. Xie, and K. Peng, Investigation of the characteristics of the intensity noise of singly resonant active second-haronic generation, J. Opt. Soc. A. B 17(10), (000). 9. M. Tsunekane, N. Taguchi, and H. Inaba, High-power, efficient, low-noise, continuous-wave all-solid-state Ti:sapphire laser, Opt. Lett. 1(3), (1996). 10. J. Belfi, J. Galli, G. Giusfredi, and F. Marin, Intensity noise of an injection-locked Ti:sapphire laser: analysis of the phase-noise-to-aplitude-noise conversion, J. Opt. Soc. A. B 3(7), (006). 11. S. Witte, R. T. Zinkstok, W. Hogervorst, and K. S. E. Eikea, Control and precise easureent of carrierenvelope phase dynaics, Appl. Phys. B 78(1), 5 1 (004). 1. Y. Yaaoto, S. Machida, and O. Nilsson, Aplitude squeezing in a pup-noise-suppressed laser oscillator, Phys. Rev. A 34(5), (1986). 13. A. Lucianetti, Th. Graf, R. Weber, and H. P. Weber, Thero-optical properties of transversely puped coposite YAG rods with Nd-doped core, IEEE J. Quantu Electron. 36(), 0 7 (000). 14. L. Fengqin, Y. Lin, S. Yuei, Z. Yaohui, Z. Kuanshou, and P. Kunchi, All-solid-state CW 1.9 W TEM 00 ode green laser, Chin. J. Lasers 36(6), (009). 15. Y. Zheng, F. Li, Y. Wang, K. Zhang, and K. Peng, High-stability single-frequency green laser with a wedge Nd:YVO 4 as a polarizing bea splitter, Opt. Coun. 83(), (010). 16. M. Bouafia, H. Bencheikh, L. Bouaaa, and H. Weber, M quality factor as a key to astering laser bea propagation, Proc. SPIE 5456, (004). 17. L. Huadong, S. Jing, L. Fengqin, W. Wenzhe, C. Yougui, and P. Kunchi, Copact, stable, tunable Ti:Sapphire laser, Chin. J. Lasers 37(5), (010). 18. H. P. Yuen, and V. W. S. Chan, Noise in hoodyne and heterodyne detection, Opt. Lett. 8(3), (1983). 19. W. Yiin, L. Yupu, and Z. Yinghua, Influence of the pup bea ode in a longitudinally puped CW Ti:sapphire laser, Chin. J. Lasers A3(), (1996). (C) 011 OSA 17 January 011 / Vol. 19, No. / OPTICS EXPRESS 1344

2 0. J. Harrison, A. Finch, D. M. Rines, G. A. Rines, and P. F. Moulton, Low-threshold, cw, all-solid-state Ti:Al( )O( 3) laser, Opt. Lett. 16(8), (1991). 1. A. J. Alfrey, Modeling of longitudinally puped CW Ti:Sapphire laser oscillators, IEEE J. Quantu Electron. 5(4), (1989).. C. C. Harb, T. C. Ralph, E. H. Huntington, I. Freitag I, D. E. McClelland, and H. A. Bachor, Intensity-noise properties of injection-locked lasers, Phys. Rev. A 54(5), (1996). 3. C. Becher, and K.-J. Boller, Intensity noise properties of Nd:YVO 4 icrochip lasers puped with an aplitude squeezed diode laser, Opt. Coun. 147(4-6), (1998). 4. H. Nagai, M. Kue, I. Otha, H. Shiizu, and M. Kazuura, Noise generation in laser diode-puped solid state lasers due to ode hopping of puping laser diodes, in Conference on Lasers and Electro-Optics, Vol. 1 of 199 OSA Technical Digest Series (Optical Society of Aerica, Washington, D. C., 199), paper CWG T. Baer, Large-aplitude fluctuations due to longitudinal ode coupling in diode-puped intracavity-doubled Nd:YAG lasers, J. Opt. Soc. A. B 3(9), (1986). 1. Introduction All-solid-state continuous-wave (CW) single-frequency tunable Ti:sapphire lasers with copact configuration and high efficiency have been extensively applied to high-sensitive laser spectroscopy, quantu counications, high-precision interferoetry and so on owing to their broad tunable wavelength range fro 700 n to 1000 n [1]. Recent years, when Ti:sapphire lasers are used in the experiental researches of laser cooling of atos, quantu optics and quantu inforation, ore and ore attentions have to be paid in reducing intensity noises of their output light since the extra noises on laser sources will severely influence the experiental results [ 4]. Ralph and Harb established a theoretical odel based on quantu echanics to express the effect of different noise sources on the intensity noises of the output light fro lasers [5]. Successively, Harb et al. experientally copared the intensity noises of two sets of Nd:YAG ring lasers puped by a single-eleent diode laser (SEDL) or by a diode-laser array (DLA), respectively [6]. They showed that the intensity noise of the Nd:YAG laser depends on vacuu fluctuations as well as on puping source noise and deonstrated that the seiclassical rate-equation odel was not sufficient to describe the noise behavior of the lasers since it is unable to involve the influence of nonclassical vacuu fluctuations on the intensity-noise spectru. Using the quantu echanical odel suggested in Ref [5], they successful described the observed intensity-noise spectru of the lasers. Later the odel was used to study the intensity noise of LD-puped Nd:YVO 4, Nd:YAP lasers [7] and single-frequency-doubling lasers [8], respectively. In 1996, Masaki Tsunekane et al. copared the intensity noises of tunable Ti:sapphire lasers puped by an Ar-ion laser with that puped by an all-solid-state green laser and showed that the intensity noises of the output light fro the Ti:sapphire laser puped by Ar-ion laser was orders of agnitude around 0.5 MHz higher than that puped by the all-solid-state laser [9]. However, they didn t consider the influence of the longitudinal-ode construction of the puping source. In 006, Jacopo Belfi et al. studied the noise properties of an injectionlocked Ti:sapphire laser and deonstrated the strong influence of the phase-noises of the injected seed-laser on the intensity noises of the output light [10]. In 004, S. Witter et al. studied the influences of the puping source on the carrier-envelope offset phase of a 10-fs pulse Ti:sapphire laser, and pointed out that the use of a single-longitudinal-ode puping source is advantageous when the carrier-envelope phase stabilization is required [11]. So far, the influences of the longitudinal-ode structure of puping sources on the operating characteristics of a CW single-frequency Ti:sapphire laser have not been discussed to the best of our knowledge. To investigate the influences of the longitudinal-ode structure of the puping sources on the intensity noises of the output light fro a puped CW Ti:sapphire laser, we design and build two sets of all-solid-state green lasers which have different configuration and longitudinal-ode structure: one with single-transverse-ode but ulti-longitudinal odes (MLM) and another one with single-longitudinal-ode (SLM). The intensity noise spectra of the SLM and MLM and the puped Ti:sapphire lasers are experientally easured with selfhoodyne detectors, respectively. The experiental results point out that the noise features of the output light of the Ti:sapphire laser puped by the SLM syste are significantly (C) 011 OSA 17 January 011 / Vol. 19, No. / OPTICS EXPRESS 1345

3 iproved in coparison with that puped by the MLM syste, and the puping efficiency of the SLM syste is uch higher than that of the MLM syste. When the MLM puping syste was replaced by the SLM puping syste, the intensity noise of the Ti:sapphire laser at the resonant relaxation oscillation (RRO) frequency was decreased fro 4 db to 19 db, the critical frequency reaching the quantu noise liit (QNL) was reduced fro 7 MHz to.5 MHz, and the threshold puping power was decreased fro 5.6 W to.1 W. By eans of the transfer-function-type theories [1] and the solutions developed by Ralph et al. [5] as well as the technique and the procedure outlined by Harb et al. [6], we obtained the theoretical predictions of the intensity noise spectra of the Ti:sapphire laser output based on the experiental paraeters for the MLM and the SLM puping systes, respectively. It is shown that the easured noise spectru of the SLM puping syste basically agrees with the theoretical prediction but for the MLM puping syste, the agreeent is not very well. The physical reasons of the disagreeent will be analyzed in the section 4.. Experiental setups At first, we briefly introduce the configurations of the MLM and SLM puping systes (T- IVB and F-VII B, Yu Guang Co., Ltd.). Both of the are the intracavity frequency-doubled all-solid-state lasers with the fundaental wavelength of 1064 n and doubling-frequency wavelength of 53 n, the puping sources of which are the CW fiber-bundled laser diodes (LDs) with the axiu output powers of 30 W for the MLM syste and 60 W for the SLM syste respectively (FB01L4511 and LIMO60-F400-DL 808-EX116, LIMO Lissotschenko Mikrooptik GbH). The diaeter and the Nuerical Aperture (NA) of the output coupling fiber for both LDs are 400 μ and 0.. The coposite Nd:YVO 4 -YVO 4 rod consisting of the undoped end cap of 5 -length and 0.3 (0.) at. % Nd-doped part of 8 (15) -length serves as the laser aterial for the MLM (SLM) syste. The use of the coposite laser crystal can iniize the effect of the theral lens during the laser operation [13]. The lithiu triborate LiB 3 O 5 (LBO) crystals with the diensions of 3 3 and are used for the frequency-doubling crystals in the MLM and the SLM syste, respectively. The teperature of the LBO crystals is well controlled at the phase-atching teperature of 148 C by a teperature controller with a precision of 0.1 C (YG-1HC, Yu Guang Co., Ltd.). The resonant cavities of the MLM and the SLM systes are the threeirror folded cavity [14] and the four-irror ring cavity [15], respectively. To ensure unidirectional operation of the SLM syste, an optical diode is inserted into its ring cavity. The axial output power of 8 W at 53 n is obtained under the LD puping powers of 8 W (40 W) at 808 n for the MLM (SLM) puping syste. Although both MLM and SLM systes are in a single-transverse-ode configuration, the easured quality-factors (M ) for the MLM and the SLM syste at the sae power of 8 W are less than 1.5 and 1.1, respectively. The larger the value of M is, the worse the quality of the bea transverse-ode is [16]. Thus the SLM syste has saller spot size at the focus in the Ti:sapphire crystal than that of the MLM syste, which results in that the SLM syste has higher puping efficiency than that of the MLM syste. (C) 011 OSA 17 January 011 / Vol. 19, No. / OPTICS EXPRESS 1346

4 Fig. 1. (Color online) Experiental setup of easuring the intensity noise of all-solid-state CW single-frequency tunable Ti:sapphire laser. f 1, f : Lens, BRF: Birefringent filter, OD: Optical diode, HWP 1, HWP, HWP 3: Half-wave 53 n, HWP 4, HWP 5: Half-wave 780 n, PBS 1, PBS : 53 n, PBS 3, PBS 4: 780 n, PD 1, PD, PD 3, PD 4: Photo-detector. The scheatic diagra of the all-solid-state frequency-tunable and single-frequency CW Ti:sapphire laser (CTSL-I, Yu Guang Co., Ltd.) is shown in Fig. 1. The puping source is the MLM or the SLM syste. The lenses f 1 and f for an optical coupling syste to couple the puping laser at 53 n into the resonant cavity of the Ti:sapphire laser. A sall part of the puping laser is reflected by a bea-splitter (M 1 ) for the easureents of the puping noises and the puping power. The ring resonator of the Ti:sapphire laser consists of four irrors (M -M 5 ) in a figure-eight configuration [17]. A Brewster-cut gain aterial (Ti:sapphire crystal), a ulti-plate birefringent filter (BRF) for tuning in a broad frequencyband, an optical diode (OD) for ensuring unidirectional operation of laser and an etalon for ode-selecting are placed in the resonator. The input coupler (M ) is coated with 95% transission at 53 n and the output coupler is coated with 3.1% transission at n. The half-wave plate HWP 1 is used for the polarization alignent of the puping laser with respect to the optical axis of the Ti:sapphire crystal. HWP 3 (HWP 5 ), the polarizing-beasplitter PBS (PBS 4 ) and the two silicon photo-diodes PD 1, PD (PD 3, PD 4 ) (S3399) copose the self-hoodyne-detector for easuring the intensity noises of the puping sources (Ti:sapphire laser). The optical signals detected by PD 1 -PD 4 are aplified by the integrated aplifiers (CLC45) and then the aplified photo currents of PD 1 and PD (PD 3 and PD 4 ) are cobined with a negative or positive power cobiner (+/). The su and the subtract photocurrents stand for the intensity noise and the corresponding quantu noise liit (QNL), respectively [18]. Finally, the noise spectra of the su (subtract) photocurrents are analyzed by a spectral analyzer (SA) with the resolution bandwidth (RBW) of 30 khz and the video bandwidth (VBW) of 30 Hz. HWP (HWP 4 ) and PBS 1 (PBS 3 ) are used for controlling the laser power detected by the self-hoodyne-detector and the power eter serves as the power onitor. (C) 011 OSA 17 January 011 / Vol. 19, No. / OPTICS EXPRESS 1347

5 3. Experiental results Fig.. (Color online) Longitudinal-ode structure of the puping sources. (a) The SLM puping syste. (b) The MLM puping syste. Figure (a) and (b) show the longitudinal-ode structures of the SLM (a) and the MLM (b) puping source which are obtained by scanning the F-P interferoeter. The MLM puping syste has coplex and rando longitudinal-ode configuration, thus it can be concluded that the severe ode-hopping and ode-copetition effects exist in the puping syste which ust significantly change the intensity noise property of the puped Ti:sapphire laser. The dependences of the output powers of the Ti:sapphire laser upon the puping powers fro the SLM (a) and the MLM (b) syste are shown in Fig. 3. The threshold puping powers for the SLM and MLM syste are.1 W and 5.6 W, respectively. The obtained power of Ti:sapphire laser puped by the SLM syste is uch higher than that puped by the MLM syste under sae puping power, that is because the transverse-ode quality of the SLM puping syste (M -1.1) is uch better than that of the MLM puping syste (M -1.5), thus using the SLM puping syste we can obtain the saller waist spot of the puping light in the Ti:sapphire crystal and the higher puping efficiency [19 1]. (C) 011 OSA 17 January 011 / Vol. 19, No. / OPTICS EXPRESS 1348

6 Fig. 3. (Color online) Output power of CW single-frequency tunable Ti:sapphire laser versus puping power with different puping sources. (a) The SLM syste as puping source. (b) The MLM syste as puping source. Fig. 4. (Color online) Intensity noise spectru of the Ti:sapphire laser copared with that of the SLM puping source. (a) Intensity noise of the SLM puping syste. (b) Intensity noise of the Ti:sapphire laser. Figure 4 and 5 show the intensity noise spectra of the Ti:sapphire laser (b) copared with that of the puping source (a) for the SLM (Fig. 4) and the MLM (Fig. 5) syste, respectively. In the experient the power of both SLM and MLM puping systes with the wavelength of 53 n is aintained at 8 W. Under this puping level the output powers of the Ti:sapphire laser at 780 n are about W and 700 W for the SLM and the MLM puping syste, respectively (See Fig. 3 for details). For perforing the noise spectru easureents in Fig. 4 and 5, the laser power injected into the hoodyne detectors for all four optical beas is precisely adjusted to 30 W with the intensity adjusters consisting of half-wave plates (HWP -HWP 5 ) and polarizing-bea-splitters (PBS 1 -PBS 4 ). The optical attenuations for the puping laser of 8 W and the Ti:sapphire laser of W (700 W) are 0.03/8 and 0.03/ (0.03/0.7), respectively. The extra attenuation of the puping power, which is 4-ties (11.5-ties) larger than the attenuation of the Ti:sapphire laser puped by the SLM (MLM) syste, has been taken into account in the noise spectra of Fig. 4 and 5 by appropriate (C) 011 OSA 17 January 011 / Vol. 19, No. / OPTICS EXPRESS 1349

7 noralization []. The intensity-noise spectra are plotted relative to the QNL on a log-log scale, i. e. 10log 10 (V f ) versus log 10 (ω/π) and 0 db indicates that the noise level equals to the QNL. The frequency and the agnitude of the RRO for the Ti:sapphire laser puped by the SLM (MLM) syste are 850 khz (75 khz) and 19 db (4 db) above the QNL. At lower frequencies fro 0.1 MHz to 0.6 MHz (close to the RRO) the intensity noise level of the Ti:sapphire laser puped by the SLM syste (Fig. 4(b)) is basically atched with that of the puping source (Fig. 4(a)), but at the region higher than 0.6 MHz, the intensity noise profile of the Ti:sapphire laser is not in good agreeent with that of the puping source. For the MLM puping syste (Fig. 5(b)) only at the frequency region fro 100 khz to 175 khz, the intensity noise level of the Ti:sapphire laser agrees with that of the puping source (Fig. 5(a)). At frequencies higher than 175 khz, the intensity noise of the Ti:sapphire laser is higher than that of the puping source. It eans that only at lower frequency the intensity noise fro the puping sources was transferred to the Ti:sapphire laser. In both SLM and the MLM systes, the intensity noise of Ti:sapphire laser reaches the QNL alost siultaneously with its puping source [.5 MHz for SLM (Fig. 4); 7MHz for MLM (Fig. 5)]. It should be entioned that the easureents of the noise spectra are ipleented fro 0.1 MHz to 10 MHz in our experients, since below 0.1 MHz the influences of the electronic noise fro the detectors cannot be neglected and the gain of the electronic aplifiers is less than the required value, thus the observed noise spectra cannot represent the real intensity noise of the easured laser and above 10 MHz all noise spectra have reached the QNL. Fig. 5. (Color online) Intensity noise spectru of the Ti:sapphire laser copared with that of the MLM puping source. (a) Intensity noise of the MLM puping syste. (b) Intensity noise of the Ti:sapphire laser. 4. Quantu theoretical prediction copared with experiental easureent According to the transfer-function forula of the noise sources developed in Ref [5], the intensity-noise spectru of the Ti:sapphire laser is expressed by V f : G G 4 8 l l V 1 V f V vac p r l r l GJ 3 t G J 4 t 3 l V l V spont dipole V losses r l r l r l (1) (C) 011 OSA 17 January 011 / Vol. 19, No. / OPTICS EXPRESS 1350

8 where V vac, V p, V spont, V dipole and V losses are the noise inputs fro vacuu noise entering the output coupler (V vac ), pup-source intensity-noise spectru (V p ), spontaneous-eission noise (V spont ), dipole fluctuation noise (V dipole ) and noise introduced fro intracavity losses (V losses ), respectively. ω is the noise frequency. The total cavity decay rate is κ = (κ + κ l ), the coefficients κ and κ l derive fro the output coupling and intracavity losses, respectively. α is the intracavity photon nuber per ato of the lasing ode and is given by Γ is the puping rate; J 3 G t J3 () is the occupation probability of the upper lasing level; G describes the coupling of the lasing transition to the laser ode and is proportional to the stiulated-eission cross section of the transition, γ t is the rate of spontaneous eission fro the upper lasing level. G r is the frequency of the RRO. l G t is the daping rate of the RRO. The experientally easured intensity-noise spectra of the Ti:sapphire laser for the SLM (a) and the MLM (b) puping syste copared with that of the theoretical prediction based on Eq. (1) [(c) for SLM and (d) for MLM] are shown in Fig. 6. The paraeters for calculating the traces (c) and (d) are listed in Table 1. Table 1. Paraeters used to calculate the noise spectra of Fig. 6(c) and 6(d) Paraeter Trace (c) Trace (d) f RRO (khz) G (s 1 ) κ (s 1 ) γ t (s 1 ) J 3 per ato α per ato N (atos) Γ (s 1 ) These values presented here are deterined by the technique outlined by Harb et al. []. For deterining the predicted noise levels we deterined the shape for one of the noise spectra firstly, then adjusted V p and Γ to coincide with their easured values, and then produce all the other noise-spectra predictions. We selected the paraeters to ake the calculated RRO peak overlapping with the experiental RRO peak in both SLM and MLM puping cases, respectively. The RRO frequency for the SLM puping syste is 850 khz which is higher 15 khz than that for the MLM puping syste (75 khz). The agnitude of the RRO peak for the SLM puping syste is 19 db above the QNL which is 5 db lower than that of the MLM puping syste (4 db). The results are in good agreeent with the predictions of the quantu theory. Since the SLM puping laser has a saller waist spot and saller ode volue in the Ti:sapphire crystal than that of the MLM puping laser, the puping rate of the SLM syste ust be faster than that of the MLM syste under the sae puping power, which results in that the RRO frequency of the SLM syste is higher and its RRO peaks is lower [3]. Copared with the RRO peak LD-puped Nd:YAG laser presented in Ref [6], the width of RRO peak of Ti:sapphire laser is wider. That is because the life tie of the laser upper level of the Ti:sapphire crystal is uch shorter than that of Nd:YAG, thus the Ti:sapphire active ediu has higher daping. For the SLM puping syste, the theoretical prediction (c) and the experiental noise spectru (a) agree quite well at and beyond the RRO frequency. However, for the MLM puping syste, the predicted width of the RRO peak (d) is wider than that experientally easured (b) and the easured noise spectru beyond the RRO frequency is higher than that of theoretical prediction (d). We can see that beyond the RRO frequency the three traces of Fig. 6(a), 6(c) and 6(d) alost overlap, which eans that just as the quantu theoretical prediction the noise spectru of the Ti:sapphire laser puped by the SLM syste was not affected by the puping noise beyond the RRO frequency. However, for the MLM syste the intensity noise of Ti:sapphire laser (b) is uch (C) 011 OSA 17 January 011 / Vol. 19, No. / OPTICS EXPRESS 1351

9 higher. It eans that the severe ode-hopping phenoena exist in the MLM puping syste which change significantly the intensity noise spectru of Ti:sapphire laser as pointed out in Ref [6]. and [4]. Fig. 6. (Color online) Ti:sapphire intensity noise spectra copared with the quantu prediction for the noise profile. (a), (b) Measured intensity noise profiles when the Ti:sapphire is puped with the SLM and the MLM syste, respectively. (c), (d) The corresponding calculated profiles. Fro Fig. 4 and 5 we can see below the RRO frequency the intensity noise of the Ti:sapphire laser is ainly doinated by the noise spectru of the puping source. Not like the LD puping source with white noises used in Ref [6], an intensity-noise distribution exists in both SLM and MLM puping sources. When we drew the traces (c) and (d) of Fig. 6 using quantu odel of Ref [5], only a value of the puping noises was utilized and the distribution of the puping noise did not considered. Thus the experiental spectra below the RRO are higher than that predicted theoretically and only around the RRO peak the prediction (c) for the SLM syste agrees with the experiental trace (a). We believe that if the noise spectru distribution of the puping source is involved in the procedure for deterining the predicted noise level, the quantu theoretical prediction will be in better agreeent with the experiental results, especially for the SLM puping syste. 5. Conclusions We experientally studied the dependences of the Ti:sapphire laser upon the longitudinalode structure of the puping sources. We found that when the single-longitudinal-ode laser serves as the puping source not only the puping efficiency is enhanced but also the noise feature of the Ti:sapphire laser is iproved significantly. The laser systes with higher puping efficiency and better intensity noise spectru are very useful in scientific research and practical application. Our works provide feasible reference for designing and building high quality all-solid-state lasers. The configuration of the laser transition levels of Ti:sapphire crystal is a broad-band twolevel syste. In this case the ode-hop and the ode-copetition of the puping laser will severely affect the operation of the puped laser and increase the intensity noise of the output laser. On the other side in the MLM intracavity frequency-doubled Nd:YVO 4 puping syste with higher power of 8 W there are possibly the intercrossing saturation effect and the green proble [5] due to the existence of the frequency-doubling crystal. These effects are not involved in the Eq. (1), so the easured noise spectru of the MLM puped Ti:sapphire laser exists larger disagreeent with that predicted theoretically. For the SLM puping syste, the noise spectru at and after the RRO frequency is in good agreeent with the quantu (C) 011 OSA 17 January 011 / Vol. 19, No. / OPTICS EXPRESS 135

10 theoretical prediction. But at lower frequency the experiental curve of Fig. 6(a) and the theoretical curve of Fig. 6(c) disagree, that is because the theoretical curve of Fig. 6(c) is drew with a given value of puping noises, which is taken only for reaching good agreeent with the experiental easureent at the RRO frequency. However, the puping noise is not the white noise and thus has different value at different frequency. The noise spectru distribution of the puping source was not involved in the calculation. We believe that if the noise distribution of the puping source is considered, the theoretical calculation will be in better agreeent with the experiental results for the SLM syste. To the MLM syste, ore physical effects, such as ode-hop, ode-copetition and so on should be involved in the theoretical forula for achieving better atch between theory and experient. Acknowledgeents This research was supported by the National Basic Research Progra (973 Progra) (No. 010CB93103), NSFC Project for Excellent Research Tea (No ), and the Key Progra of NSFC (No ). (C) 011 OSA 17 January 011 / Vol. 19, No. / OPTICS EXPRESS 1353