- Email: [email protected]
An independently tunable, collinear, variable delay, two-wavelength dye laser
15 July 1998
Optics Communications 153 Ž1998. 68–72
An independently tunable, collinear, variable delay, two-wavelength dye laser R. Khare ) , S.R. Daulatabad, K.K. Sharangpani, R. Bhatnagar Laser Programme Centre for AdÕanced Technology, Indore 452013, India Received 16 December 1997; revised 23 March 1998; accepted 6 May 1998
Abstract The paper presents a novel resonator scheme consisting of two coupled dye laser resonators to obtain independently tunable and collinear two-wavelengths having adjustable delay between them. A single grating is used to provide dispersion and coupling. With 510.6 and 578.2 nm of copper vapor laser to pump Rhodamine 6G and Sulforhodamine B dyes respectively the collinear outputs could be tuned over 566 to 606 nm and 600 to 640 nm with individual bandwidths of 0.24 cmy1. By changing the path-difference between the pump beam components, the delay between the two wavelengths could be varied from 21 to 30 ns. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Two-wavelength dye laser; Coupled resonator; Rhodamine 6G; Sulforhodamine B
1. Introduction Many laser-spectroscopic techniques and applications like Coherent Anti-Stokes Raman Spectroscopy ŽCARS., pollution monitoring, sum and difference frequency generation and two-colour stepwise multiphoton ionization experiments, etc. require independently tunable and collinear two wavelengths either simultaneous or with certain delay between them. A number of dye laser resonator schemes for obtaining two-wavelength operation with collinear and noncollinear outputs are reported. The reflected and transmitted beams from Glan prism w1x, beam expander prism w2x or dielectric multilayer filter w3x have been used to obtain two-wavelength operation in a dye laser resonator. Double-wavelength operation is also demonstrated by providing feedback on two diffraction orders of a diffraction grating aligned in GIG configuration w4,5x. To obtain twowavelength operation, two gratings are aligned in Littrow mode w6,7x or GIG mode w8x in a dye laser resonator. In a Hansch type dye laser resonator, a small-angle wedge is
)
E-mail: [email protected]
inserted in the expanded part of the beam to form two independent resonators to obtain a double-wavelength laser w9x. In these resonator schemes the two wavelengths were collinear or noncollinear depending on whether the wavelengths shared the active medium w1–8x or did not share the same active medium w9x. Since a single dye was used, the separation between the two wavelengths was limited to the extremes of the spectral range of the dye. The wavelength separation was increased by using two dyes placed on spatially separated axes in the resonator to obtain noncollinear outputs which were combined outside the resonator w10x. In all these resonator schemes since the dyes were pumped simultaneously, the two-wavelength operation was simultaneous. In this paper we present a novel resonator scheme which gives independently tunable and collinear two wavelength outputs having adjustable delay between them using a single grating. The separation between the two wavelengths is not limited because two different dyes are used. It is known that in case of a CVL pumped Rhodamine 6G dye laser, the 578.2 nm component is removed from the pump beam due to its deteriorating effect on the performance of the dye laser w11–18x. In the proposed scheme a
0030-4018r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 0 3 0 - 4 0 1 8 Ž 9 8 . 0 0 2 5 7 - 0
R. Khare et al.r Optics Communications 153 (1998) 68–72
dye having absorption at 578.2 nm can be placed in one of the resonators to effectively use this component.
2. Experimental set-up A single diffraction grating can be simultaneously used in two dye laser resonators to provide dispersion for spectral narrowing in each dye laser if the two dye lasers are setup on either side of the grating. Further if the grating is aligned to have equal incidence angles in both dye lasers then the same grating can couple the dye laser outputs collinearly because the zeroth order beam from one dye laser would propagate along the optical axis of the other dye laser. The experimental set-up based on this fact is shown in Fig. 1. The pump source was a home-made copper-vapour laser ŽCVL. giving average power of 10 W Ž6 kHz. with 6.5 W at 510.6 nm and 3.5 W at 578.2 nm. The 510.6 nm wavelength from the CVL beam was separated and reflected by dichroic mirrors M 1 and M 2 and focused by a cylindrical lens C 1 Ž f s 8.5 cm. on 2 mM solution of Rhodamine 6G ŽLambda Physik, Lambdachrome w Laser Dye. in ethanol. The 578.2 nm wavelength, transmitted through M 1, was focused by a cylindrical lens C 2 Ž f s 8.5 cm. on 3.9 mM solution of Sulforhodamine B ŽSIGMA, S-9012, dye content f 70%. in ethanol. Both solutions were circulated through home-made dye-cells at a flow rate of about 4 lpm. The two dye lasers, DL-1 with Rhodamine 6G and DL-2 with Sulforhodamine B, were aligned on each side of a diffraction grating, G Ž2400 grrmm., oriented in GIG configuration in both dye lasers. A wedge W and a 100% reflecting mirror M 4 formed the two ends of the cavity for the DL-1. Two 100% reflecting mirrors M 3 and M 5 formed the two ends of the cavity for
Fig. 1. Experimental arrangement: M 1 , M 2 : dichroic mirrors; C 1 , C 2 : cylindrical lenses; P1 , P2: pinholes; DC-1, DC-2: dye cells; M 3 , M 4 , M 5 : 100% reflecting mirrors; G: diffraction grating; W: output wedge; a 1 and a 2 indicate angles of incidence on the grating in DL-1 and DL-2 respectively.
69
the DL-2. The grating was aligned such that a 1 s a 2 s a . Since the output of DL-1 is absorbed in DL-2, the combined output could not be taken through M 3 and the 0th order beam from G was used as the laser output in DL-2. The collinear output was taken through the output coupler W because the output of DL-2 was not absorbed in DL-1. The pinholes P1 and P2 were used to minimise ASE and to align DL-1 and DL-2 on collinear axes. The output coupler W and the mirror M 3 formed a broadband cavity in DL-2 making the tuning mirror M 5 ineffective. To suppress this broadband lasing, the grazing incidence angle was reduced to 858 and the reflectivity of W was also reduced to about 4%. The resonator lengths of DL-1 and DL-2 were 25 and 30 cm respectively. The temporal profiles of pump and dye laser beams were recorded using biplanar photodiodes ŽiTL, S-1. and a two channel oscilloscope ŽLecroy, 9350 A.. The laser pulses were made to traverse equal optical paths to reach the respective biplanar photodiodes. The dye laser output power was measured by a power meter ŽCOHERENT model 210.. The spectral tuning ranges were recorded using a 0.5 m monochromator ŽPACIFIC Precision Instrument, MP-1021. and an oscilloscope ŽL & T, 4074..
3. Results and discussion Fig. 2 shows the temporal behavior of pump and dye laser pulses. It is seen that the 578.2 nm component evolved after a delay of about 12 ns with respect to the 510.6 nm component ŽFig. 2a.. The Rhodamine 6G dye laser pulse Ž l1 . evolved after a typical delay of about 8 ns with respect to the 510.6 nm ŽFig. 2b.. The pulsewidths Žat base. of the pump and dye laser pulses were about 55 and 26 ns respectively. Fig. 2c shows that the Sulforhodamine B dye laser pulse Ž l2 . evolved after a typical delay of about 26 ns with respect to the 578.2 nm. The pulse widths Žat base. of the pump and dye laser pulses were about 58 ns and 24 ns respectively. The long delay in build up of l 2 could be due to the fact that not only Rhodamine 6G is more efficient than Sulforhodamine B but also the average power available at 578.2 nm is about one third that of 510.6 nm leading to lower gain in DL-2. In the experimental set-up the 510.6 nm component traversed more path length than the 578.2 nm component before being focused on the respective dye-cells. The delay between l1 and l 2 can be varied by changing the path-difference between the two pump pulses ŽFig. 3.. A delay of about 30, and 21 ns was obtained for path-difference of about 44, and 319 cm respectively ŽFig. 3a and 3b.. In the resonator scheme, the performance of the Rhodamine 6G dye laser was evaluated by blocking the 578.2 nm pump beam. The average output power of Rhodamine 6G dye laser was 170 mW Žh f 2.6%. at 572 nm. The efficiency can be increased using prism beam-expanders in
70
R. Khare et al.r Optics Communications 153 (1998) 68–72
Fig. 3. Delay between l1 and l2 : Ža. 30 and Žb. 21 ns.
Fig. 2. Temporal pulse shapes: Ža. 510.6 and 578.2 nm, Žb. 510.6 nm and l1 and Žc. 578.2 nm and l2 .
the resonator. The spectral range of the Sulforhodamine B dye laser was not within the absorption range of the Rhodamine 6G w19x, therefore it is not absorbed in unpumped Rhodamine 6G. Hence, in the resonator scheme, the performance of the Sulforhodamine B dye laser could be evaluated by blocking the 510.6 nm pump beam. The average output power of the Sulforhodamine B dye laser was 50 mW Žh f 1.4%. at 618 nm. It was observed during alignment of the two lasers that l2 was amplified when the two beams were made collinear. This is due to the fact that the laser beam from DL-2 reached the active medium of Rhodamine 6G before the termination of the 510.6 nm pump laser and its spectral range was within the emission range of the Rhodamine 6G, i.e., 526 to 670 nm w20x. In two-wavelength collinear operation the output of the Sulforhodamine B dye laser was amplified to 110 mW Ž l2 s 618 nm. when the delay between l2 and l1 was 30 ns.
R. Khare et al.r Optics Communications 153 (1998) 68–72
71
lasers without losses expected in external beam combiners. Delays of this order are required in two-colour stepwise multiphoton ionisation experiments where delays are obtained by external optical delay lines w21x or electronic delays introduced in the triggering of the two pump lasers w22x. Fig. 4 shows the spectral tuning ranges of one wavelength along with the variation in intensity of the other fixed wavelength in the collinear two-wavelength output. In Fig. 4a the curves ŽA. and ŽB. show tuning ranges of l 2 when it traversed through the unpumped and pumped Rhodamine 6G dye media respectively indicating that the l2 wavelength is amplified. While recording the tuning range of l2 by rotating M 5 , the intensity at a fixed l1 Ž580 nm. was also monitored. It was observed that the intensity of l1 Ž580 nm. remained unchanged as l 2 was tuned from 600 to 640 nm ŽFig. 4a.. The delay between l1 and l2 was 30 ns. The measurements were repeated for l1 by rotating M 4 keeping l 2 fixed. The intensity of l2 Ž625 nm. remained constant when l1 was tuned from 566 to 606 nm ŽFig. 4b.. This is because the two wavelengths did not share the Rhodamine 6G active medium simultaneously. However, when the delay was reduced to about 21 ns, the intensity at fixed wavelength did not remain constant because of temporal overlap in the pumped Rhodamine 6G medium ŽFig. 4c.. The configuration of equal grating incidence angles resulted in having equal spectral linewidths of both l1 and l2 . By externally dispersing the beam and using a solid etalon wFSR s 0.66 cmy1 and Finesss 14x, the time-averaged spectral linewidths of 0.24 cmy1 were observed for each of them.
4. Conclusion In conclusion a resonator scheme is demonstrated in which a single grating provides dispersion for two dye lasers and couples them to give independently tunable two wavelength operation with variable delay in a collinear beam. The two wavelengths can be tuned over 566 to 606 nm and 600 to 640 nm with individual bandwidths of 0.24 cmy1. By changing the path-difference between the pump beam components the delay between the two wavelengths could be varied from 21 to 30 ns.
Acknowledgements Fig. 4. Spectral tuning range of Ža. l2 , l1 s 580 nm Ž – P – ., delay s 30 ns4 with Rhodamine 6G unpumped ŽA. and pumped ŽB.. Žb. l1 Ž – ( – . l2 s625 nm Ž – P – ., delay s 30 ns4. Žc. l1 Ž – ( – . l2 s605 nm Ž – I – ., delay s 21 ns4.
The delay between two pump wavelengths from the same laser is effectively used, for the first time, to introduce inherent delay between the collinear outputs of the two dye
The authors are grateful to Mr. R.K. Mishra and Mr. Jagdish Kumar for maintenance of the copper vapour laser.
References w1x H.S. Pilloff, Appl. Phys. Lett. 21 Ž1972. 339. w2x L.G. Nair, Appl. Phys. 20 Ž1979. 97.
72
R. Khare et al.r Optics Communications 153 (1998) 68–72
w3x Y. Saito, T. Teramura, A. Nomura, T. Kano, Appl. Optics 22 Ž1983. 1799. w4x Y. Prior, Rev. Sci. Instrum. 50 Ž1979. 259. w5x S.G. Dinev, I.G. Koprinkov, K.V. Stamenov, K.A. Stankov, C. Radzewicz, Optics Comm. 32 Ž1980. 313. w6x E.F. Zalewski, R.A. Keller, Appl. Optics 10 Ž1973. 2773. w7x A.A. Friesem, U. Ganiel, G. Neumann, Appl. Phys. Lett. 23 Ž1973. 249. w8x L.G. Nair, K. Dasgupta, IEEE J. Quantum Electron. 16 Ž1980. 111. w9x H. Lotem, R.T. Lynch, Appl. Phys. Lett. 27 Ž1975. 344. w10x K. Ishikawa, S. Muto, H. Matsuzawa, Appl. Phys. Lett. 54 Ž1989. 1637. w11x Y. Maruyama, M. Kato, T. Arisawa, Jap. J. Appl. Phys. 30 Ž1991. L748. w12x T.S. Petrov, N.V. Sabotinov, S.T. Trendafilov, Optics Comm. 92 Ž1992. 291. w13x L.V. Masarnovskii, A.N. Soldatov, V.B. Sukhanov, Sov. J. Quantum. Electron. 9 Ž1979. 900.
w14x A.A. Pease, W.M. Pearson, Appl. Optics 16 Ž1977. 57. w15x Y. Arai, H. Niki, S. Adachi, T. Takeda, T. Yamanaka, C. Yamanaka, Technology Reports Osaka University, 36 Ž1860. Ž1986. 361. w16x S.A. Kostritsa, V.A. Mishin, Quantum. Electron. 25 Ž1995. 516. w17x K.I. Zemskov, A.A. Isaev, M.A. Kazaryan, G.G. Petrash, A.V. Adamushko, M.V. Belokov, A.N. Rubinov, P.G. Evtukhovich, Sov. J. Quantum. Electron. 6 Ž1976. 727. w18x K. Dasgupta, L.G. Nair, IEEE J. Quantum Electron. 26 Ž1990. 189. w19x U. Brackmann, Lambdachrome w Laser Dyes, Lambda Physik 1st ed., 1988, pp. 111–116. w20x P.R. Hammond, IEEE J. Quantum Electron. 15 Ž1979. 624. w21x P.N. Bajaj, K.G. Manohar, B.M. Suri, K. Dasgupta, R. Talukdar, P.K. Chakraborti, P.R.K. Rao, Appl. Phys. B 47 Ž1988. 55. w22x V.K. Mago, B. Lal, A.K. Ray, R. Kapoor, S.D. Sharma, P.R.K. Rao, J. Phys. B 20 Ž1987. 6021.
Optics Communications 153 Ž1998. 68–72
An independently tunable, collinear, variable delay, two-wavelength dye laser R. Khare ) , S.R. Daulatabad, K.K. Sharangpani, R. Bhatnagar Laser Programme Centre for AdÕanced Technology, Indore 452013, India Received 16 December 1997; revised 23 March 1998; accepted 6 May 1998
Abstract The paper presents a novel resonator scheme consisting of two coupled dye laser resonators to obtain independently tunable and collinear two-wavelengths having adjustable delay between them. A single grating is used to provide dispersion and coupling. With 510.6 and 578.2 nm of copper vapor laser to pump Rhodamine 6G and Sulforhodamine B dyes respectively the collinear outputs could be tuned over 566 to 606 nm and 600 to 640 nm with individual bandwidths of 0.24 cmy1. By changing the path-difference between the pump beam components, the delay between the two wavelengths could be varied from 21 to 30 ns. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Two-wavelength dye laser; Coupled resonator; Rhodamine 6G; Sulforhodamine B
1. Introduction Many laser-spectroscopic techniques and applications like Coherent Anti-Stokes Raman Spectroscopy ŽCARS., pollution monitoring, sum and difference frequency generation and two-colour stepwise multiphoton ionization experiments, etc. require independently tunable and collinear two wavelengths either simultaneous or with certain delay between them. A number of dye laser resonator schemes for obtaining two-wavelength operation with collinear and noncollinear outputs are reported. The reflected and transmitted beams from Glan prism w1x, beam expander prism w2x or dielectric multilayer filter w3x have been used to obtain two-wavelength operation in a dye laser resonator. Double-wavelength operation is also demonstrated by providing feedback on two diffraction orders of a diffraction grating aligned in GIG configuration w4,5x. To obtain twowavelength operation, two gratings are aligned in Littrow mode w6,7x or GIG mode w8x in a dye laser resonator. In a Hansch type dye laser resonator, a small-angle wedge is
)
E-mail: [email protected]
inserted in the expanded part of the beam to form two independent resonators to obtain a double-wavelength laser w9x. In these resonator schemes the two wavelengths were collinear or noncollinear depending on whether the wavelengths shared the active medium w1–8x or did not share the same active medium w9x. Since a single dye was used, the separation between the two wavelengths was limited to the extremes of the spectral range of the dye. The wavelength separation was increased by using two dyes placed on spatially separated axes in the resonator to obtain noncollinear outputs which were combined outside the resonator w10x. In all these resonator schemes since the dyes were pumped simultaneously, the two-wavelength operation was simultaneous. In this paper we present a novel resonator scheme which gives independently tunable and collinear two wavelength outputs having adjustable delay between them using a single grating. The separation between the two wavelengths is not limited because two different dyes are used. It is known that in case of a CVL pumped Rhodamine 6G dye laser, the 578.2 nm component is removed from the pump beam due to its deteriorating effect on the performance of the dye laser w11–18x. In the proposed scheme a
0030-4018r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 0 3 0 - 4 0 1 8 Ž 9 8 . 0 0 2 5 7 - 0
R. Khare et al.r Optics Communications 153 (1998) 68–72
dye having absorption at 578.2 nm can be placed in one of the resonators to effectively use this component.
2. Experimental set-up A single diffraction grating can be simultaneously used in two dye laser resonators to provide dispersion for spectral narrowing in each dye laser if the two dye lasers are setup on either side of the grating. Further if the grating is aligned to have equal incidence angles in both dye lasers then the same grating can couple the dye laser outputs collinearly because the zeroth order beam from one dye laser would propagate along the optical axis of the other dye laser. The experimental set-up based on this fact is shown in Fig. 1. The pump source was a home-made copper-vapour laser ŽCVL. giving average power of 10 W Ž6 kHz. with 6.5 W at 510.6 nm and 3.5 W at 578.2 nm. The 510.6 nm wavelength from the CVL beam was separated and reflected by dichroic mirrors M 1 and M 2 and focused by a cylindrical lens C 1 Ž f s 8.5 cm. on 2 mM solution of Rhodamine 6G ŽLambda Physik, Lambdachrome w Laser Dye. in ethanol. The 578.2 nm wavelength, transmitted through M 1, was focused by a cylindrical lens C 2 Ž f s 8.5 cm. on 3.9 mM solution of Sulforhodamine B ŽSIGMA, S-9012, dye content f 70%. in ethanol. Both solutions were circulated through home-made dye-cells at a flow rate of about 4 lpm. The two dye lasers, DL-1 with Rhodamine 6G and DL-2 with Sulforhodamine B, were aligned on each side of a diffraction grating, G Ž2400 grrmm., oriented in GIG configuration in both dye lasers. A wedge W and a 100% reflecting mirror M 4 formed the two ends of the cavity for the DL-1. Two 100% reflecting mirrors M 3 and M 5 formed the two ends of the cavity for
Fig. 1. Experimental arrangement: M 1 , M 2 : dichroic mirrors; C 1 , C 2 : cylindrical lenses; P1 , P2: pinholes; DC-1, DC-2: dye cells; M 3 , M 4 , M 5 : 100% reflecting mirrors; G: diffraction grating; W: output wedge; a 1 and a 2 indicate angles of incidence on the grating in DL-1 and DL-2 respectively.
69
the DL-2. The grating was aligned such that a 1 s a 2 s a . Since the output of DL-1 is absorbed in DL-2, the combined output could not be taken through M 3 and the 0th order beam from G was used as the laser output in DL-2. The collinear output was taken through the output coupler W because the output of DL-2 was not absorbed in DL-1. The pinholes P1 and P2 were used to minimise ASE and to align DL-1 and DL-2 on collinear axes. The output coupler W and the mirror M 3 formed a broadband cavity in DL-2 making the tuning mirror M 5 ineffective. To suppress this broadband lasing, the grazing incidence angle was reduced to 858 and the reflectivity of W was also reduced to about 4%. The resonator lengths of DL-1 and DL-2 were 25 and 30 cm respectively. The temporal profiles of pump and dye laser beams were recorded using biplanar photodiodes ŽiTL, S-1. and a two channel oscilloscope ŽLecroy, 9350 A.. The laser pulses were made to traverse equal optical paths to reach the respective biplanar photodiodes. The dye laser output power was measured by a power meter ŽCOHERENT model 210.. The spectral tuning ranges were recorded using a 0.5 m monochromator ŽPACIFIC Precision Instrument, MP-1021. and an oscilloscope ŽL & T, 4074..
3. Results and discussion Fig. 2 shows the temporal behavior of pump and dye laser pulses. It is seen that the 578.2 nm component evolved after a delay of about 12 ns with respect to the 510.6 nm component ŽFig. 2a.. The Rhodamine 6G dye laser pulse Ž l1 . evolved after a typical delay of about 8 ns with respect to the 510.6 nm ŽFig. 2b.. The pulsewidths Žat base. of the pump and dye laser pulses were about 55 and 26 ns respectively. Fig. 2c shows that the Sulforhodamine B dye laser pulse Ž l2 . evolved after a typical delay of about 26 ns with respect to the 578.2 nm. The pulse widths Žat base. of the pump and dye laser pulses were about 58 ns and 24 ns respectively. The long delay in build up of l 2 could be due to the fact that not only Rhodamine 6G is more efficient than Sulforhodamine B but also the average power available at 578.2 nm is about one third that of 510.6 nm leading to lower gain in DL-2. In the experimental set-up the 510.6 nm component traversed more path length than the 578.2 nm component before being focused on the respective dye-cells. The delay between l1 and l 2 can be varied by changing the path-difference between the two pump pulses ŽFig. 3.. A delay of about 30, and 21 ns was obtained for path-difference of about 44, and 319 cm respectively ŽFig. 3a and 3b.. In the resonator scheme, the performance of the Rhodamine 6G dye laser was evaluated by blocking the 578.2 nm pump beam. The average output power of Rhodamine 6G dye laser was 170 mW Žh f 2.6%. at 572 nm. The efficiency can be increased using prism beam-expanders in
70
R. Khare et al.r Optics Communications 153 (1998) 68–72
Fig. 3. Delay between l1 and l2 : Ža. 30 and Žb. 21 ns.
Fig. 2. Temporal pulse shapes: Ža. 510.6 and 578.2 nm, Žb. 510.6 nm and l1 and Žc. 578.2 nm and l2 .
the resonator. The spectral range of the Sulforhodamine B dye laser was not within the absorption range of the Rhodamine 6G w19x, therefore it is not absorbed in unpumped Rhodamine 6G. Hence, in the resonator scheme, the performance of the Sulforhodamine B dye laser could be evaluated by blocking the 510.6 nm pump beam. The average output power of the Sulforhodamine B dye laser was 50 mW Žh f 1.4%. at 618 nm. It was observed during alignment of the two lasers that l2 was amplified when the two beams were made collinear. This is due to the fact that the laser beam from DL-2 reached the active medium of Rhodamine 6G before the termination of the 510.6 nm pump laser and its spectral range was within the emission range of the Rhodamine 6G, i.e., 526 to 670 nm w20x. In two-wavelength collinear operation the output of the Sulforhodamine B dye laser was amplified to 110 mW Ž l2 s 618 nm. when the delay between l2 and l1 was 30 ns.
R. Khare et al.r Optics Communications 153 (1998) 68–72
71
lasers without losses expected in external beam combiners. Delays of this order are required in two-colour stepwise multiphoton ionisation experiments where delays are obtained by external optical delay lines w21x or electronic delays introduced in the triggering of the two pump lasers w22x. Fig. 4 shows the spectral tuning ranges of one wavelength along with the variation in intensity of the other fixed wavelength in the collinear two-wavelength output. In Fig. 4a the curves ŽA. and ŽB. show tuning ranges of l 2 when it traversed through the unpumped and pumped Rhodamine 6G dye media respectively indicating that the l2 wavelength is amplified. While recording the tuning range of l2 by rotating M 5 , the intensity at a fixed l1 Ž580 nm. was also monitored. It was observed that the intensity of l1 Ž580 nm. remained unchanged as l 2 was tuned from 600 to 640 nm ŽFig. 4a.. The delay between l1 and l2 was 30 ns. The measurements were repeated for l1 by rotating M 4 keeping l 2 fixed. The intensity of l2 Ž625 nm. remained constant when l1 was tuned from 566 to 606 nm ŽFig. 4b.. This is because the two wavelengths did not share the Rhodamine 6G active medium simultaneously. However, when the delay was reduced to about 21 ns, the intensity at fixed wavelength did not remain constant because of temporal overlap in the pumped Rhodamine 6G medium ŽFig. 4c.. The configuration of equal grating incidence angles resulted in having equal spectral linewidths of both l1 and l2 . By externally dispersing the beam and using a solid etalon wFSR s 0.66 cmy1 and Finesss 14x, the time-averaged spectral linewidths of 0.24 cmy1 were observed for each of them.
4. Conclusion In conclusion a resonator scheme is demonstrated in which a single grating provides dispersion for two dye lasers and couples them to give independently tunable two wavelength operation with variable delay in a collinear beam. The two wavelengths can be tuned over 566 to 606 nm and 600 to 640 nm with individual bandwidths of 0.24 cmy1. By changing the path-difference between the pump beam components the delay between the two wavelengths could be varied from 21 to 30 ns.
Acknowledgements Fig. 4. Spectral tuning range of Ža. l2 , l1 s 580 nm Ž – P – ., delay s 30 ns4 with Rhodamine 6G unpumped ŽA. and pumped ŽB.. Žb. l1 Ž – ( – . l2 s625 nm Ž – P – ., delay s 30 ns4. Žc. l1 Ž – ( – . l2 s605 nm Ž – I – ., delay s 21 ns4.
The delay between two pump wavelengths from the same laser is effectively used, for the first time, to introduce inherent delay between the collinear outputs of the two dye
The authors are grateful to Mr. R.K. Mishra and Mr. Jagdish Kumar for maintenance of the copper vapour laser.
References w1x H.S. Pilloff, Appl. Phys. Lett. 21 Ž1972. 339. w2x L.G. Nair, Appl. Phys. 20 Ž1979. 97.
72
R. Khare et al.r Optics Communications 153 (1998) 68–72
w3x Y. Saito, T. Teramura, A. Nomura, T. Kano, Appl. Optics 22 Ž1983. 1799. w4x Y. Prior, Rev. Sci. Instrum. 50 Ž1979. 259. w5x S.G. Dinev, I.G. Koprinkov, K.V. Stamenov, K.A. Stankov, C. Radzewicz, Optics Comm. 32 Ž1980. 313. w6x E.F. Zalewski, R.A. Keller, Appl. Optics 10 Ž1973. 2773. w7x A.A. Friesem, U. Ganiel, G. Neumann, Appl. Phys. Lett. 23 Ž1973. 249. w8x L.G. Nair, K. Dasgupta, IEEE J. Quantum Electron. 16 Ž1980. 111. w9x H. Lotem, R.T. Lynch, Appl. Phys. Lett. 27 Ž1975. 344. w10x K. Ishikawa, S. Muto, H. Matsuzawa, Appl. Phys. Lett. 54 Ž1989. 1637. w11x Y. Maruyama, M. Kato, T. Arisawa, Jap. J. Appl. Phys. 30 Ž1991. L748. w12x T.S. Petrov, N.V. Sabotinov, S.T. Trendafilov, Optics Comm. 92 Ž1992. 291. w13x L.V. Masarnovskii, A.N. Soldatov, V.B. Sukhanov, Sov. J. Quantum. Electron. 9 Ž1979. 900.
w14x A.A. Pease, W.M. Pearson, Appl. Optics 16 Ž1977. 57. w15x Y. Arai, H. Niki, S. Adachi, T. Takeda, T. Yamanaka, C. Yamanaka, Technology Reports Osaka University, 36 Ž1860. Ž1986. 361. w16x S.A. Kostritsa, V.A. Mishin, Quantum. Electron. 25 Ž1995. 516. w17x K.I. Zemskov, A.A. Isaev, M.A. Kazaryan, G.G. Petrash, A.V. Adamushko, M.V. Belokov, A.N. Rubinov, P.G. Evtukhovich, Sov. J. Quantum. Electron. 6 Ž1976. 727. w18x K. Dasgupta, L.G. Nair, IEEE J. Quantum Electron. 26 Ž1990. 189. w19x U. Brackmann, Lambdachrome w Laser Dyes, Lambda Physik 1st ed., 1988, pp. 111–116. w20x P.R. Hammond, IEEE J. Quantum Electron. 15 Ž1979. 624. w21x P.N. Bajaj, K.G. Manohar, B.M. Suri, K. Dasgupta, R. Talukdar, P.K. Chakraborti, P.R.K. Rao, Appl. Phys. B 47 Ž1988. 55. w22x V.K. Mago, B. Lal, A.K. Ray, R. Kapoor, S.D. Sharma, P.R.K. Rao, J. Phys. B 20 Ž1987. 6021.