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Picosecond time delay fluorimetry using a jitter-free streak camera
Volume 34, number 3
OPTICS COMMUNICATIONS
September 1980
PICOSECOND TIME DELAY FLUORIMETRY USING A JITTER-FREE STREAK CAMERA
Michael STAVOLA l~'l~r~mt'm of Chcmisto', U~lh,ersio' o f Rochester, R~dwster, 3,'eu, York 1462 Z US,4
Gerard MOUROU and Wayne KNOX L~boratory t.or Laa'r k'm'rgetics. Unirersity of Rochester, Rochester, .Yew York. 14623. US,4 Received 24 April 1980
A ,,treak camera driven with picosecond accuracy by a laser-activated cryogenic Si-switch has been used to measure the deca~ time of malachite green in wamr by a pulse fluorimetry technique. The single shot timing accuracy o1" the streak camera (a few psi corresponds to "--105; of the optical pulscwidth. The overall stability of the system allows the averaging of hundreds of laser shots without image translation improving both the signal to noise ratio and timing accuracy of the mca,qurements. The subpicosccond ti.ning accuracy afforded by shot averaging has enabled us to measure a 2 ps fluorescence decay time l\~r a low quantum yield sample with a 20 ps excitation pulse.
!. Introduction
In ~his paper we report on the operation of a non recurrent streak ca~m:ra with single-shot zero time jitter of a few picoseconds. This is accomplished by controlling the streak deflection voltage with a laser activated cryogenic Si switch [ 1 ]. The coupling of ~t'~estreak camera ~,_ndtile DC bias switching scheme ~ves rise to a system that is both extremely stable and operationally simple. The capabilities of the system are such that a fluorescent decay time of 2 ps corresponding to "-10% of the laser pulse width can be measured by a time delay fluorimetry technique. In a streak image tube a photoelectron beam, after being accelerated, is rapidly deflected across a phosphor screen. Over the past years improvements in image tube design have reduced the limit of streak camera time resomtion to about 0.5 ps [2,3]. Unfortunately, however, short and long term fluctuations of the beginning of tile streak are several hundred times tile resolution limit. This instability is due to tile lack of shot-to-shot reproducibility of the voltage ramp used to sweep the photoelectron beam across the phosphor screen. Conventional techniques for generating the driving voltage involve inherently unstable 404
avalanche-type pulsers s~.ch as high pressure spark gaps, krypton, or avalanche transistor stacks. Techniques for generating a nearly jitter-free streak deflection have been demonstrated recently. Bradley et al. [4] have driven a streak camera at a repetition rate of 140 Mllz with a RF driving voltage that is synchronized with a CW mode-locked dye laser and have achieved stable operation with a temporal fluctuation of 3 ps. Of more relevance to this work is the achievement of comparable temporal precision (-+2 ps) by Mourou and Knox [5,6] with a non recurrent laser. The high voltage driving pulse was obtained by means of a laser-activated photoconductive switch [7]. When the switching element is integrated into a wide bandwidth geometry the shape of the generated electrical pulse is solely determined by the energy and shape of the optical trigger pulse. In order to alleviate tim thermal runaway instability in the switching clement a lfigh voltage electrical bias pulse shorter than the thermal instability build up time (NM 20/~s) was used. It was pointed out [5,6] that one cause of the remaining temporal jitter was tile voltage amplitude fluctuations ofonly 1% that gave rise to fluctuations in sweep speed. From this observation it was clear that DC biased switching and laser stabilization are pre-
Volume 34, number 3
OPTICS COMMUNICATIONS
requisites for the ultimate temporal stability of the streak camera. Apparently unaware of those results, a similar technique has been used later by Margulis et al. [8]. Ajitter of +15 ps was found. A DC biased switching technique has been developed recently [ 1 ] and is used in this work to provide the ramping voltage for a streak camera. Tile extremely stable short and long term operation of the streak camera allows the accumulation of hundreds of shots. A picosecond time delay fluorimetry technique has been demonstrated with this system. Time shifts as small as 1 psec can be measured even with 20 psec actinic pulses. To demonstrate the technique the tim. rescence decay time of malachite green in water (2 psec) was measured.
2. Experimental Fig. 1 shows the experimental arrangement. Two pulses are selected from the train of a mode-locked Nd 3+ • YLF oscillator, one by a double Pockels cell switch out system (contrast >105) and one by a single Pockels cell switch out system (contrast >103),
[
and are directed along separate beam lines. The higher contrast pulse is used to irradiate a 2 mm gap cryo. genic Si-switch. The electrical pulse generated provides the deflection voltage for a Photochron I! streak tube ($20 photocathode). The lower contrast pulse is frequency doubled and directed towards a sample cell at the entrance of the streak camera. Detection of the output of the streak camera is by a four state, magnetically focused image intensifier and an optical multi. channel analyzer. The resolution of the system was focusing limited to about 5 or 6 ps, less than the width of any temporal structure to be resolved. An OMA II was used to collect and store large numbers of streaked traces that could then be averaged and background corrected. Tile cryogenic switching apparatus [ 1 ] consists of a 3 ns 50-~2 microstrip transmission line on a sapphire substrate. The microstrip line is interrupted by a block of Au-doped Si with dimensions 1 mm X 0.5 mm X 2 mm. The 1 mm thick sapphire substrate is fastened to a brass plate that is in contact with a liquid nitrogen cold trap. Tile apparatus is enclosed in a chamber at a pressure of a 1 millitorr to prevent condensation on tile cold components. The stripline is biased by a 3
A0.524
!
Nd 3' : YLF osmllatm
September 1980
pm
re.
Oouble ! / ~ pulse
I
swich-out
I I 1.048/Jrn
i j L '
3ns Cryogenic SI swi 3kV power supply
Adjustable delay line
5 k~?,
[ ,,-OMA
m
i
Image intensifier "
T
2. ,.j, Image - converter tube
Fig. 1. Fxperimental arrangement. 405
Volume 34, number 3
OPTICS COMMUNICATIONS
kV power supt~ly through a 5 k~2 resistor. At this bias ~t~ltage the cryogenic Si-sw~tch passes a 10/aA current. [!tvon irradiation by a laser pulse the Au-doped Si becomes conducting thereby discharging the biased stripline, The fast pulse produced is shown in fig. 2. (A 1,5 ns cha~e line biased to 2.4 kV was used for this oscillogrmn.) The laser energy of 150/aJ -+ 10% that activates the Si-switch is about 20 times the value n,xluired to provide 50% switching efficiency. Laser ener~" and optical pulse shape fluctuations are believed to be responsible for the residual jitter of a few picosezonds. In fi'-3-3 are shown two traces of crystal violet emission in glycerol that demonstrate the stability of our s.vstem. Each trace is an average of 70 laser shots that were accumulated in 20 minute time intervals separated by 3 hours. The long term drift as evidenced by a displacement of the half point is about 0.6 ps, or roughtly 2/3 of an OMA channel. This is a severe test of the system because data is usually accumulated over a i/2 hour interval. Similar experiments were repeated with the consistent result being that after the s3.'stem had warmed tip, drift over an afternoon was less than a picosecond (one OMA cilannel) demonstrating excellent stability. When a piece of glass a few
i
"
September 1980
millimeters thick is inserted in the frequency doubled beam the arrival of the excitation pulse is delayed by a few picoseconds. In fig. 4 are presented streaked traces of the average of 30 laser shots, separated by a delay time corresponding to the addition of 2.1 mm of ~ass to the beam line. From the index of refraction of the glass we estimate the time delay should be 3.9 ps compared to the observed average shift of 3.9 --. 0.5 ps. Also shown in fig. 4 is the difference of the two traces. Amplitude of the signal difference is proportional to the introduced time delay. The signal to noise ratio of the signal difference indicates that, by averaging only over few ten of shots this technique can give rise to subpicosecond precision. The low timing jitter that characterizes our streak camera system allows a local sweep speed calibration to be made that does not involve the generation of a train of pulses with a bounce etalon and is thus independent of field curvature which can cause errors. A coaxial adjustable delay line can be used to change the arrival time of the electrical deflection pulse and thereby provide a shift of :he streak trace which can be measured. We note that the lack of zero time and
T
.
t -
.
.
.
.
.
.
•
.
o
.
.
•
.
°
•
.
.
.
.
.
11
.
.
.
°
.
kv
.
%
J
S/ ~1 ns (Two Divisions)
__
1 -30
I
I
-20
l
I
L .... I....
-10
0 TIME
I~. 2. l-ast pulse produced by switching tile cryogenic Siswitch with 1.06 um light.
406
L_
1 10
__L_
I
20
I____J__
30
(psec)
Fig. 3. Two series of 70 acctllltulated shots of tryst;.|! violel in glycerol fluorescence taken 3 hours apart.
Volume 34, number 3
OPTICS COMMUNICATIONS
September 1980
1 m
.5 W
Q.
4
'I" m
B
1
2
3
4
5
6
7
LIFETIME (psec) Fig. 5. Shift from the zero time versus the 1/e fluorescence decay time. I -30
I -20
t -10
I 0
I 10
I 20
I 30
TIME (plec)
l:gi. 4. Two series of 30 accumulated shots of the optical excitation. The optical delay path has been offal by 3.9 ps. In the bollonl, lhe difference between the two series showing the subpicosecond timing precision. Optical pulse width: 18 ps.
sweep speed tluctuations allow the entire streak trace Io be used and permit signal multiplexing. Exponential decay times that are much less than the temporal width of the excitation pulse can be measured by a time delay technique. The convolution of a gaussian excitation profile and an exponential characterized by a I/e time of nmch less than the excitation pulse width is easily shown to be approximately gaussian in shape but with its maximum shifte,J from that of the excitation profile by a time equal tc the decay time of the exponential [9]. The tinting accuracy of our streak camera system allows us to measure such time shifts. It is important tt, realize that dispersive effects taking place in the collection optics and streak-image tube make it necessary to calibrate zero time for the wavelength of the signal (rather than using the maximum of the 0.530 tam excitation directly which can give errors estimated to be "1 ps). In our experiments a dye whose emission spectrum was similar to that of the system to be studied but with a decay time that is long compared with the excitalion pulse width was used to provide a zero time
calibration. Crystal violet in glycerol was used as the long lifetime reference because of the close match of its emission spectrum with that of malaclffte green in water. The 1/e decay t.,ne of the crystal violet sample was measured to be 85 ps. Because of the high viscositi~' of the glycerol and the very short decay time of malachite green in water, the effects of rotational reorientation were ignored. The half point of the rise for the 85 ps decay thne convolution is used as ,'he timing mark. Because of the finite lifetime of the emission, the half point is not exactly at zero time as defined by the maximum of the excitation but precedes it by 1.2 ps. In fig. 5 is plotted the shift from zero time versus 1[e decay time for tile convolution of an exponential and an 18 ps FWHM gaussian. As the decay time of the exponential increases, the sensitivity of the shift decreases so that this technique is most useful for decay times less than about one-half of the pulse width. A malachite green sample that was 2 × 10 -3 M in distilled water and a crystal violet sample of 5 × i0 --5 M in glycerol were prepared. Emission measurements were made using a 1 mm path lengfll cell that was hnaged at .f/1.9 onto the photocathode of the streak camera. A cylindrical lens was used to focus the excitation beam to a sharp line in the sample, the inaage of w!fich was streaked, so that slits did not have to be used to obtain good time resolution. Tiffs technique optimized the collection of fluorescent lieu and the use of the excitation pulse. 407
Volume 34, m, mln'r 3
OPTICS COMMUNICATIONS
September 1980
3. Conclusion Crystal Violel
We have used a nearly jitter-free streak camera system to demonstrate a picosecond time delay fluorimetry technique. The extremely stable DC biased Si-switch that we have used to drive the streak camera allows hundreds of laser shots to be averaged so that the picosecond decay time of samples with a low quantum yield emission can be measured with an enhanced signal to noise ratio.
L M~,a~cl~t
Acknowledgements
,=
!
:
i
l
I
I
I
I
-15
-10
-5
0
5
10
15
20
I
TIME (psec)
Fig. 6. Malachite in water fluorescence against the crystal ~iolet in glycerol fluorescence. Both signals are obtained ut.~m accumulation of 100 shots. The shift from the zero time is clearly observed.
M. Stavola wishes to acknowledge the support of ONR (grant N00014-78-00596). This work was partially supported by the following sponsors: Exxon Research and Engineering Company, General Electric Company, Northeast Utilities, Empire State Electric Energy Research Corporation, New York State Energy Research and Development Authority, and the Eastman Kodak Company,
References In fig. 6 are displayed the OMA traces of the emission of maiactfite green in water averaged over 120 Laser shots and also of crystal violet in glycerol averaged over 80 laser shots. Th.~ shift of the center of the malachite green trace from the 1[2 point of the rise of tl~e crystal violet emission is measured to be 2'..8 + 1 ps. Two corrections are to be made. The 1/2 l:~int of the crys':ai violet emission preceeds the maximum of the excitation by 0.9 ps if the effect of the t'mite lifetime of the crystal violet fluorescence and also the difference in the indices of refraction for the different solvents are considered. This makes the shift of malachite green emission with respect to the excitation i.q + ~ ps corresponding to a 1/e decay time of 2: + 1 ps. This result is in excellent agreement with the r:~easurement of Ippen et al. [10] of 2.1 ps as determined from absorption recovery.
~.08
[1] M. Stavola, M. Sceats and (;. Mourou, Optics Comm. 34 (1980) 4o9. [2] For a good review on streak cameras, see for instance: D.J. Bradley, G.H.C. New, Proc. IEEE 62 (1974) 313. [31 D.J. Bradley, Optics and Laser Technoiog. 11 (1979) 23. [41 MC. Adams, D.J. Bradley, W. Sibbett and J.R. Taylor, Chem. Phys. Lett. 66 (1979)428. [51 W. Knox, W. Friedman and G. Mourou, CLEA. 1979 meeting paper I-2. [61 G. Mourou and W. Knox, Appl. Phys. Lett. 36 (1980) 623. [71 G. Mourou and W. Knox, Appl. Phys. Lett. 35 (1979) 492. [81 W. Margulis, W. Sibett, J.R. Taylor and D.J. Bradley, Optics Comm. 32 (1980) 331.
[9] G. Mourou and M.M. Mallcy, Optics C()mm. 13 (1975) 41"2.
[lOl E.P. Ippen, C.V. Shank and A. Bergman, Chem. Phys. Lett. 38 (1976) 611.
OPTICS COMMUNICATIONS
September 1980
PICOSECOND TIME DELAY FLUORIMETRY USING A JITTER-FREE STREAK CAMERA
Michael STAVOLA l~'l~r~mt'm of Chcmisto', U~lh,ersio' o f Rochester, R~dwster, 3,'eu, York 1462 Z US,4
Gerard MOUROU and Wayne KNOX L~boratory t.or Laa'r k'm'rgetics. Unirersity of Rochester, Rochester, .Yew York. 14623. US,4 Received 24 April 1980
A ,,treak camera driven with picosecond accuracy by a laser-activated cryogenic Si-switch has been used to measure the deca~ time of malachite green in wamr by a pulse fluorimetry technique. The single shot timing accuracy o1" the streak camera (a few psi corresponds to "--105; of the optical pulscwidth. The overall stability of the system allows the averaging of hundreds of laser shots without image translation improving both the signal to noise ratio and timing accuracy of the mca,qurements. The subpicosccond ti.ning accuracy afforded by shot averaging has enabled us to measure a 2 ps fluorescence decay time l\~r a low quantum yield sample with a 20 ps excitation pulse.
!. Introduction
In ~his paper we report on the operation of a non recurrent streak ca~m:ra with single-shot zero time jitter of a few picoseconds. This is accomplished by controlling the streak deflection voltage with a laser activated cryogenic Si switch [ 1 ]. The coupling of ~t'~estreak camera ~,_ndtile DC bias switching scheme ~ves rise to a system that is both extremely stable and operationally simple. The capabilities of the system are such that a fluorescent decay time of 2 ps corresponding to "-10% of the laser pulse width can be measured by a time delay fluorimetry technique. In a streak image tube a photoelectron beam, after being accelerated, is rapidly deflected across a phosphor screen. Over the past years improvements in image tube design have reduced the limit of streak camera time resomtion to about 0.5 ps [2,3]. Unfortunately, however, short and long term fluctuations of the beginning of tile streak are several hundred times tile resolution limit. This instability is due to tile lack of shot-to-shot reproducibility of the voltage ramp used to sweep the photoelectron beam across the phosphor screen. Conventional techniques for generating the driving voltage involve inherently unstable 404
avalanche-type pulsers s~.ch as high pressure spark gaps, krypton, or avalanche transistor stacks. Techniques for generating a nearly jitter-free streak deflection have been demonstrated recently. Bradley et al. [4] have driven a streak camera at a repetition rate of 140 Mllz with a RF driving voltage that is synchronized with a CW mode-locked dye laser and have achieved stable operation with a temporal fluctuation of 3 ps. Of more relevance to this work is the achievement of comparable temporal precision (-+2 ps) by Mourou and Knox [5,6] with a non recurrent laser. The high voltage driving pulse was obtained by means of a laser-activated photoconductive switch [7]. When the switching element is integrated into a wide bandwidth geometry the shape of the generated electrical pulse is solely determined by the energy and shape of the optical trigger pulse. In order to alleviate tim thermal runaway instability in the switching clement a lfigh voltage electrical bias pulse shorter than the thermal instability build up time (NM 20/~s) was used. It was pointed out [5,6] that one cause of the remaining temporal jitter was tile voltage amplitude fluctuations ofonly 1% that gave rise to fluctuations in sweep speed. From this observation it was clear that DC biased switching and laser stabilization are pre-
Volume 34, number 3
OPTICS COMMUNICATIONS
requisites for the ultimate temporal stability of the streak camera. Apparently unaware of those results, a similar technique has been used later by Margulis et al. [8]. Ajitter of +15 ps was found. A DC biased switching technique has been developed recently [ 1 ] and is used in this work to provide the ramping voltage for a streak camera. Tile extremely stable short and long term operation of the streak camera allows the accumulation of hundreds of shots. A picosecond time delay fluorimetry technique has been demonstrated with this system. Time shifts as small as 1 psec can be measured even with 20 psec actinic pulses. To demonstrate the technique the tim. rescence decay time of malachite green in water (2 psec) was measured.
2. Experimental Fig. 1 shows the experimental arrangement. Two pulses are selected from the train of a mode-locked Nd 3+ • YLF oscillator, one by a double Pockels cell switch out system (contrast >105) and one by a single Pockels cell switch out system (contrast >103),
[
and are directed along separate beam lines. The higher contrast pulse is used to irradiate a 2 mm gap cryo. genic Si-switch. The electrical pulse generated provides the deflection voltage for a Photochron I! streak tube ($20 photocathode). The lower contrast pulse is frequency doubled and directed towards a sample cell at the entrance of the streak camera. Detection of the output of the streak camera is by a four state, magnetically focused image intensifier and an optical multi. channel analyzer. The resolution of the system was focusing limited to about 5 or 6 ps, less than the width of any temporal structure to be resolved. An OMA II was used to collect and store large numbers of streaked traces that could then be averaged and background corrected. Tile cryogenic switching apparatus [ 1 ] consists of a 3 ns 50-~2 microstrip transmission line on a sapphire substrate. The microstrip line is interrupted by a block of Au-doped Si with dimensions 1 mm X 0.5 mm X 2 mm. The 1 mm thick sapphire substrate is fastened to a brass plate that is in contact with a liquid nitrogen cold trap. Tile apparatus is enclosed in a chamber at a pressure of a 1 millitorr to prevent condensation on tile cold components. The stripline is biased by a 3
A0.524
!
Nd 3' : YLF osmllatm
September 1980
pm
re.
Oouble ! / ~ pulse
I
swich-out
I I 1.048/Jrn
i j L '
3ns Cryogenic SI swi 3kV power supply
Adjustable delay line
5 k~?,
[ ,,-OMA
m
i
Image intensifier "
T
2. ,.j, Image - converter tube
Fig. 1. Fxperimental arrangement. 405
Volume 34, number 3
OPTICS COMMUNICATIONS
kV power supt~ly through a 5 k~2 resistor. At this bias ~t~ltage the cryogenic Si-sw~tch passes a 10/aA current. [!tvon irradiation by a laser pulse the Au-doped Si becomes conducting thereby discharging the biased stripline, The fast pulse produced is shown in fig. 2. (A 1,5 ns cha~e line biased to 2.4 kV was used for this oscillogrmn.) The laser energy of 150/aJ -+ 10% that activates the Si-switch is about 20 times the value n,xluired to provide 50% switching efficiency. Laser ener~" and optical pulse shape fluctuations are believed to be responsible for the residual jitter of a few picosezonds. In fi'-3-3 are shown two traces of crystal violet emission in glycerol that demonstrate the stability of our s.vstem. Each trace is an average of 70 laser shots that were accumulated in 20 minute time intervals separated by 3 hours. The long term drift as evidenced by a displacement of the half point is about 0.6 ps, or roughtly 2/3 of an OMA channel. This is a severe test of the system because data is usually accumulated over a i/2 hour interval. Similar experiments were repeated with the consistent result being that after the s3.'stem had warmed tip, drift over an afternoon was less than a picosecond (one OMA cilannel) demonstrating excellent stability. When a piece of glass a few
i
"
September 1980
millimeters thick is inserted in the frequency doubled beam the arrival of the excitation pulse is delayed by a few picoseconds. In fig. 4 are presented streaked traces of the average of 30 laser shots, separated by a delay time corresponding to the addition of 2.1 mm of ~ass to the beam line. From the index of refraction of the glass we estimate the time delay should be 3.9 ps compared to the observed average shift of 3.9 --. 0.5 ps. Also shown in fig. 4 is the difference of the two traces. Amplitude of the signal difference is proportional to the introduced time delay. The signal to noise ratio of the signal difference indicates that, by averaging only over few ten of shots this technique can give rise to subpicosecond precision. The low timing jitter that characterizes our streak camera system allows a local sweep speed calibration to be made that does not involve the generation of a train of pulses with a bounce etalon and is thus independent of field curvature which can cause errors. A coaxial adjustable delay line can be used to change the arrival time of the electrical deflection pulse and thereby provide a shift of :he streak trace which can be measured. We note that the lack of zero time and
T
.
t -
.
.
.
.
.
.
•
.
o
.
.
•
.
°
•
.
.
.
.
.
11
.
.
.
°
.
kv
.
%
J
S/ ~1 ns (Two Divisions)
__
1 -30
I
I
-20
l
I
L .... I....
-10
0 TIME
I~. 2. l-ast pulse produced by switching tile cryogenic Siswitch with 1.06 um light.
406
L_
1 10
__L_
I
20
I____J__
30
(psec)
Fig. 3. Two series of 70 acctllltulated shots of tryst;.|! violel in glycerol fluorescence taken 3 hours apart.
Volume 34, number 3
OPTICS COMMUNICATIONS
September 1980
1 m
.5 W
Q.
4
'I" m
B
1
2
3
4
5
6
7
LIFETIME (psec) Fig. 5. Shift from the zero time versus the 1/e fluorescence decay time. I -30
I -20
t -10
I 0
I 10
I 20
I 30
TIME (plec)
l:gi. 4. Two series of 30 accumulated shots of the optical excitation. The optical delay path has been offal by 3.9 ps. In the bollonl, lhe difference between the two series showing the subpicosecond timing precision. Optical pulse width: 18 ps.
sweep speed tluctuations allow the entire streak trace Io be used and permit signal multiplexing. Exponential decay times that are much less than the temporal width of the excitation pulse can be measured by a time delay technique. The convolution of a gaussian excitation profile and an exponential characterized by a I/e time of nmch less than the excitation pulse width is easily shown to be approximately gaussian in shape but with its maximum shifte,J from that of the excitation profile by a time equal tc the decay time of the exponential [9]. The tinting accuracy of our streak camera system allows us to measure such time shifts. It is important tt, realize that dispersive effects taking place in the collection optics and streak-image tube make it necessary to calibrate zero time for the wavelength of the signal (rather than using the maximum of the 0.530 tam excitation directly which can give errors estimated to be "1 ps). In our experiments a dye whose emission spectrum was similar to that of the system to be studied but with a decay time that is long compared with the excitalion pulse width was used to provide a zero time
calibration. Crystal violet in glycerol was used as the long lifetime reference because of the close match of its emission spectrum with that of malaclffte green in water. The 1/e decay t.,ne of the crystal violet sample was measured to be 85 ps. Because of the high viscositi~' of the glycerol and the very short decay time of malachite green in water, the effects of rotational reorientation were ignored. The half point of the rise for the 85 ps decay thne convolution is used as ,'he timing mark. Because of the finite lifetime of the emission, the half point is not exactly at zero time as defined by the maximum of the excitation but precedes it by 1.2 ps. In fig. 5 is plotted the shift from zero time versus 1[e decay time for tile convolution of an exponential and an 18 ps FWHM gaussian. As the decay time of the exponential increases, the sensitivity of the shift decreases so that this technique is most useful for decay times less than about one-half of the pulse width. A malachite green sample that was 2 × 10 -3 M in distilled water and a crystal violet sample of 5 × i0 --5 M in glycerol were prepared. Emission measurements were made using a 1 mm path lengfll cell that was hnaged at .f/1.9 onto the photocathode of the streak camera. A cylindrical lens was used to focus the excitation beam to a sharp line in the sample, the inaage of w!fich was streaked, so that slits did not have to be used to obtain good time resolution. Tiffs technique optimized the collection of fluorescent lieu and the use of the excitation pulse. 407
Volume 34, m, mln'r 3
OPTICS COMMUNICATIONS
September 1980
3. Conclusion Crystal Violel
We have used a nearly jitter-free streak camera system to demonstrate a picosecond time delay fluorimetry technique. The extremely stable DC biased Si-switch that we have used to drive the streak camera allows hundreds of laser shots to be averaged so that the picosecond decay time of samples with a low quantum yield emission can be measured with an enhanced signal to noise ratio.
L M~,a~cl~t
Acknowledgements
,=
!
:
i
l
I
I
I
I
-15
-10
-5
0
5
10
15
20
I
TIME (psec)
Fig. 6. Malachite in water fluorescence against the crystal ~iolet in glycerol fluorescence. Both signals are obtained ut.~m accumulation of 100 shots. The shift from the zero time is clearly observed.
M. Stavola wishes to acknowledge the support of ONR (grant N00014-78-00596). This work was partially supported by the following sponsors: Exxon Research and Engineering Company, General Electric Company, Northeast Utilities, Empire State Electric Energy Research Corporation, New York State Energy Research and Development Authority, and the Eastman Kodak Company,
References In fig. 6 are displayed the OMA traces of the emission of maiactfite green in water averaged over 120 Laser shots and also of crystal violet in glycerol averaged over 80 laser shots. Th.~ shift of the center of the malachite green trace from the 1[2 point of the rise of tl~e crystal violet emission is measured to be 2'..8 + 1 ps. Two corrections are to be made. The 1/2 l:~int of the crys':ai violet emission preceeds the maximum of the excitation by 0.9 ps if the effect of the t'mite lifetime of the crystal violet fluorescence and also the difference in the indices of refraction for the different solvents are considered. This makes the shift of malachite green emission with respect to the excitation i.q + ~ ps corresponding to a 1/e decay time of 2: + 1 ps. This result is in excellent agreement with the r:~easurement of Ippen et al. [10] of 2.1 ps as determined from absorption recovery.
~.08
[1] M. Stavola, M. Sceats and (;. Mourou, Optics Comm. 34 (1980) 4o9. [2] For a good review on streak cameras, see for instance: D.J. Bradley, G.H.C. New, Proc. IEEE 62 (1974) 313. [31 D.J. Bradley, Optics and Laser Technoiog. 11 (1979) 23. [41 MC. Adams, D.J. Bradley, W. Sibbett and J.R. Taylor, Chem. Phys. Lett. 66 (1979)428. [51 W. Knox, W. Friedman and G. Mourou, CLEA. 1979 meeting paper I-2. [61 G. Mourou and W. Knox, Appl. Phys. Lett. 36 (1980) 623. [71 G. Mourou and W. Knox, Appl. Phys. Lett. 35 (1979) 492. [81 W. Margulis, W. Sibett, J.R. Taylor and D.J. Bradley, Optics Comm. 32 (1980) 331.
[9] G. Mourou and M.M. Mallcy, Optics C()mm. 13 (1975) 41"2.
[lOl E.P. Ippen, C.V. Shank and A. Bergman, Chem. Phys. Lett. 38 (1976) 611.