TWI239128B - A blue-light generating femtosecond wavelength-tunable non-collinear optical parametric amplifier - Google Patents

Abstract

The present invention discloses a means of the generation of tunable femtosecond pulses from 380 nm to 465 nm near the degenerate point of a 405 nm pumped type-I BBO noncollinearly phase-matched optical parametric amplifier (NOPA). The tunable UV/blue radiation is obtained from sum frequency generation (SFG) between the OPA output and the residual fundamental beam at 810 nm and cascaded second harmonic generation (SHG) of OPA. With a pumping energy of 75 mJ at 405 nm, the optical conversion efficiency from the pump to the tunable SFG is more than 5% and the efficiency of SHG of the OPA is about 2%.

Description

1239128 V. Description of the invention (1) 1 · TECHNICAL FIELD OF THE INVENTION The present invention relates to an optical parameter amplifier, and in particular, to the use of a series of non-linear optical mixing to generate a wavelength adjustable femtosecond (Femt〇sec〇nd) ) Non-collinear optical parameter amplifier to provide blue light and near-ultraviolet (38〇_460nm) —continuously adjustable optical parameter amplifier. 2. Prior art

In recent years, the use of Blu-ray has been increasing. High-density storage is the hottest industry. The application of this band in the field of biotechnology and environmental monitoring is particularly important. In addition, time-resolved and frequency-resolved studies, real-time studies of molecular dynamics, and spectral methods

The above applications have shown great development potential of blue light and near-ultraviolet light. However, both blue and near UV sources and detectors are lacking. In the past ten years, the development of non-linear crystals and laser technology has become more and more mature, making tunable wavelength light sources in this band possible. How to generate better and more convenient light sources and increase efficiency are important research and development directions. Optical parameter amplifiers are an important means of generating tunable wavelengths, but it is very difficult to directly generate blue light from optical parameter amplifiers. Usually, they need to undergo another non-linear optical process, such as frequency doubling (freqUency doububng) or sum-frequency generation. ), Increasing the complexity of the system and

Page 6 1239128 V. Description of the invention (2) Cost. In the currently published literature, the optical parameter amplification process is used to generate wavelength-tunable light sources, such as `` Ultrafast optical parametric amplifiers 丨 '' published by Giulio Cerullo in Review of Scientific Instruments 74, 1-17 (2003) in 2003. ; Howe-Siang Tan is equivalent to "Generation and amplification of ultrashort shaped pulses in the visible by a two-stage noncollinear optical parametric process'1" published in Opt Lett. 26, 1812-1814 (20 0 1) in 2001. P.Tzankov equals to 2002 published in Opt · Commun ·, 20 3, 107 ~ (2002) of " Broadband opti cal parametric amplification in the near UV-VIS "and Osvay equals to 2002 published in Appl. Phys. B: Lasers Opt. B74, S163 ~ 20 02 (20 0 2), Broadband amplification of ultraviolet laser pulses ", in the paper of Howe-Siang Tan et al., Is designed as a framework for generating visible light parameter amplification systems in general , But limited by the absorption characteristics of nonlinear crystals, the shortest output adjustable range is about 450 nm; in the paper by P. Tzankov et al. Osvay et al. , Is to directly use the non-linear optical parameter process to generate a wavelength-tunable light source; the designed structure is changed to a shorter wavelength excitation light source, so the output adjustable range is 346-453nm; and its structure is a general optical parameter amplification structure, Its focus is to use the base light source as a higher-order co-frequency to generate a shorter wavelength excitation light source to generate the required blue light and near-ultraviolet electromagnetic waves, but it will make the system more complicated and caused by multi-wavelength mirrors.

1239128 V. Description of the invention (3) Cost increases. In the paper of 0 s v a y et al., The emphasis is on combining the frequency of the generated field with the wavelength output, which complicates the system and causes re-signature due to the frequency combining process itself. It is also prone to unstable output due to mechanical problems. Also in Petro, it was published in 1994 by J. Appl. Phys. 76, 7704-7712 (1994), `` Eetens ion of tuning range of a femtosecond T i: Sapph i re laser amplifier through cascaded second-order nonlinear frequency conversion processes The architecture of the design in the paper is based on the optical mixing or combining architecture of the latter stage, which is equal to that of Chao-Kuei Lee, published in Opt · Express 11, 2070- 1708 (2003) in 2003. ， Generation of femtosecond laser pulses tunable from 380 nm to 465 nm via cascaded nonlinear optical mixing in a nonco1 linear optical parametric amplifier with a type-I phase matched BBO crystal ” Non-collinear optical parameter amplifiers have different principles.

Basu's U.S. Patent No. 5,144,629;] U.S.A. Patent No. 5,751,4 72, etc .; and U.S. Patent No. 5,7 51,4 7 2 by Stamm et al. The general optical parameter amplification architecture is adopted, and only signals (signal) and unwanted light (idler) are output. The conventionally known blue-green light output optical parameter amplifier is essentially the short wavelength required for frequency combination generation using the generated long wavelength output, or

Page 8 1239128 V. Description of the invention (4) Use a higher frequency to generate a shorter wavelength excitation light source. The disadvantages are that the original wavelength of the excitation light is not easy to produce (the high-order harmonic frequency conversion efficiency is poor), the group speed is not matched & with (Group Velocity Mismatch) and short-wavelength coating is not easy, and the cost is high. It is a combined frequency architecture, which makes the system more complicated, which is quite inconvenient and limited for use. ^ Therefore, the present invention addresses the shortcomings of the prior art, and proposes a non-collinear optical parameter amplifier with a tunable femtosecond (Femtosecond) wavelength. 3. SUMMARY OF THE INVENTION The object of the present invention is to provide a femtosecond non-collinear optical parameter amplifier with adjustable wavelength by using non-linear optical mixing in series. Cascaded Sum Frequency Generation of Non-col 1 inear Optical Parametric Amplification) provides a continuously adjustable blue-green light source generating device. A second object of the present invention is to provide a femtosecond non-collinear optical parameter amplifier with a wavelength adjustable by using a non-linear optical mixing in series, and using a non-linear optical mixing phenomenon in series, only a non-linear optical crystal is needed. It can provide a blue light source with a wavelength band (38 0 ~ 46 5nm), and its wavelength is continuously adjustable. It is still another object of the present invention to provide a method for utilizing non-linear optical mixing in series.

1 ^ 11 IIM Page 9 1239128 V. Description of the invention (5) A blue light parameter amplification system that generates a femtosecond non-collinear optical parameter amplifier with adjustable wavelength, which can be implemented at a lower cost and a simpler method. In order to achieve the above and other objectives, the present invention proposes a femtosecond non-collinear optical parameter amplifier with a tunable wavelength generated by series-connected non-linear optical mixing, which includes at least: an optical parametric amplification (OPA) excitation The frequency doubling device of the light source enters the incident light into the BB0 crystal for frequency doubling to become blue light after frequency doubling; a white light generating device that generates a low-frequency oscillating frequency and emits incident light into CaF2 f (window) to generate seed light; a rotation The rotating platform for crystals enables non-collinear optical parameter amplification crystals to rotate around the rotation axis; a plurality of lenses, silver mirrors and reflectors guide light to non-collinear optical parameter amplification crystals; The collinear optical parameter amplifying crystal, the crystal axis of which can be rotated around the rotation axis to adjust and change the wavelength of Cascaded Sum Frequency Generation (SFG). The above and other objects and advantages of the present invention will be more fully understood with reference to the following drawings and description of the preferred embodiment. 4. For implementation, please refer to FIG. 1 a, which is a schematic structural diagram of a string-joint-frequency optical parameter amplifier system 100 according to an embodiment of the present invention. The string-joint-frequency optical parameter amplifier of the first embodiment includes an excitation generator. Light source 丨 6 wavelength doubling device 12, a low-frequency white light generating device 15 (not shown), and a generation wave

12 ^ 9128 V. Description of the invention (6) Non-linear optical crystal 14 for adjustable non-collinear optical parameter amplification and some fixed sample fixtures, mirrors, time delay devices, and rotating platforms for rotating crystals (all (Not shown), so that the crystal 14 can be rotated along the rotation axis 22 to provide a crystal axis 22 that can change direction, thereby changing the phase matching conditions of the crystal. A Ti-sapphire laser, whose output power is greater than lm J / pulse, with near-infrared incident light 15 with a wavelength of ~ 80 Onm, when it enters the 5/95 beam splitter 1, about 5%. The light is reflected by the beam splitter 1 through the reflection aperture 4, and is reflected by two silver mirrors 9 on the moving platform 10, 180 degrees of reflection. After being focused by the 5 cm positive lens 5, the seed light 1 is generated by the 2 square meter CaF 2 window 6. 7. After passing through a parabolic lens 7 with a focal length of 5 cm, a silver mirror 9 and a silver-plated focusing lens 11 with a focal length of 15 cm, the seed light 17 is focused and incident into the 2 mm thick BB0 crystal 14 for PA. On the other hand, most of the incident light 15 passes through the 5/95 spectroscopy 1 and passes through adjustable attenuators, namely 30 cm positive lens 2 and 15 cm negative lens 3. The two silver mirrors 9 reflect at 180 degrees and enter the BB0 crystal 12 with a thickness of 200 micrometers for frequency doubling to become blue light 16 ~ 400nm after frequency doubling. This second statement is a wave (second harmonic genera ti on, SHG ) For pumping (non-col 1 inear Optical)

Parametric Amplification (NOPA), this blue light 16 is passed through a blue light total reflection mirror 8 and a silver-plated focusing lens with a focal length of 15 cm. The blue light 16 is focused into a 2 mm thick 0PA BB0 crystal 14. When you want to generate optical parameter amplification signal (Optical Parametric

Page 11 1239128 ~ V. Description of the invention (7)

Generation (OPG) seed light 17 travels in the direction shown in Figure lb, which corresponds to the generated unwanted light 20 (idler) 20 and the fundamental frequency of the remaining white light excitation light 19 to produce a string junction frequency (C ascaded Sum Frecjuency Generation (SFG) 21, the wavelength of this combined frequency will also be tunable as the rotation axis 23 of the crystal axis 22 direction is changed, that is to provide a continuously adjustable blue light output optical parameter amplifier. Please refer to Fig. 2a. Fig. 2a is a schematic diagram of the parameter amplification process and the optical axis of the string-joint-frequency non-linear optical parameter amplifier corresponding to Fig. 1. The symbols in the figure are defined as follows: & are the angle between the signal light 17 and the unwanted light 20 and the optical axis 22, and α is the seed light 17 and the excitation light (the super light generated by the OA excitation light). Fluorescence) The angle between 18 and 5 is the angle between the generated unwanted light 20 and the remaining fundamental frequency excitation light 丨 9 which is the remaining angle, which is relative to the angle between the generated combined frequency SFG21 and the unwanted light 20. As shown in Figure 2a, this architecture uses the idler light generated by 0PA when the excitation light 18 and white light injection signal (seeder) 17 are in a type 1 noncollinear structure and the angle is ^. ) 20 will automatically meet the phase matching conditions with the remaining bases, plus light to generate the combined frequency, and then automatically generate a series of combined frequency process. This embodiment also has a theoretical simulation comparison. When the string joining frequency occurs, the energy conservation and direction are matched as follows:

1239128 V. Description of the invention (8)

Tita ^ YQ = + ^^ 8〇〇 (1)

== ^ k [o) + BkW, 1 phase 1 ^, ωι, ω800 are frequencies of combined frequency 21, idler 20 f and hV, kSFG, kl, k8 ° are combined frequency 21, useless, respectively The wave vector of light and fundamental frequency 19, (e) and (〇) shown in the superscript are only U: polarized in the anterior axis direction, perpendicular to the light vehicle is 0 light (o-ray), otherwise e, " E ^ ay). When (1) is satisfied at the same time, it can be obtained, which can be sorted into [kWco ^ + kWj (2) We compare the results of this theoretical calculation with the experimental data of Example 1. Please refer to Figure 2b, vertical coordinate It is the adjustable range of SFG, and the horizontal axis is the angle between the injected signal (seeder) and the OPA excitation light. The solid black line is the adjustable range of SFG at different cool angles of the theoretical nose, the solid square is the optimal phase matching wavelength for calculation, the solid star is the wavelength obtained when the energy conversion output at the included angle is the maximum, the hollow circle and the cross point For the adjustable range obtained at -8 · 4 and _14 degrees, we can find that there is a good contrast between the experiment and the theory. The wavelength of the maximum output conversion efficiency has a good coincidence with the optimal phase matching point of the theoretical calculation. The adjustable range between two different angles is also within the theoretical range, and the measurement results have a good contrast with the theoretical values.

1239128

1239128 Brief description of the drawings 5. Brief description of the drawings: FIG. 1a is a schematic structural diagram of a string junction frequency optical parameter amplifier system in the embodiment of the present invention. Figure 1b is a schematic diagram of the crystal rotation axis and optical path in the system of Example 1 of the present invention. Figure 2a is a schematic diagram of the relative relationship between the crystal string splicing frequency, the remaining 8000 nm excitation light, the OPA excitation light, the opa signal, the OPA idler, and the optical axis of the crystal in the non-collinear optical parameter amplifier of the embodiment of the present invention. Figure 2b is the theoretical adjustable range when the included angle is -8 · 4 and -14 degrees according to the embodiment of the present invention. Figure 3a is the output frequency spectrum of the string junction frequency obtained by rotating the 0PA crystal when the included angle is -8 degrees in the embodiment of the present invention. Explanation of symbols: 1 · 5/95 light splitter 3 · 1 5 cm negative lens 5 · 5 cm positive lens 7 · focal length 5 cm parabolic lens 9. silver mirror 2 · 30 cm positive lens 4. aperture 6. 2 mm thick CaF2 window 8 · Blue light total reflection mirror 1 〇 · Mobile platform

Page 15 1259128 Brief description of the diagram 11 · Focal length 1 5 minutes Silver focusing lens 1 2 · 2 0 0 micron frequency bb 〇 crystal 13. The angle between OPA excitation light and seed light 14. 2 mm thick BBO crystal for OPA 15 Near-infrared ~ 800 nm incident light 16 · Blue light after frequency doubling ~ 4 0 0 nm 17 · Seed light produced by 2 mm thick CaF2 window 18 · Super fluorescence 19 produced by OPA excitation light · OPA fundamental frequency excitation Light 20 · OPA unwanted light (idler) 21 · Cascaded SFG 22. Optical axis 23 · OPA crystal rotation direction

1〇〇 · String junction frequency optical parameter amplifier system

Page 16

Claims (1)

1239128 6. Scope of patent application 1. A femtosecond non-collinear optical parameter amplifier connected in series with a non-linear optical mixing to generate a tunable wavelength includes at least: an optical source for generating optical parametric amplification (Optical Parametric Amplification, 0 pA) Frequency doubling device, which transmits the incident light into the BB0 crystal for frequency doubling, and becomes blue light of frequency doubling light; a white light generating device that generates a low frequency, and emits incident light into the CaF 2 window to generate seed light; for rotating crystals Rotate the platform so that the non-collinear optical parameter magnification crystal can rotate around the rotation axis; a plurality of lenses, silver mirrors and reflectors guide the light to the non-collinear optical parameter magnification crystal; For optical parameter amplification crystals, the crystal axis can be rotated around the rotation axis to change the wavelength of an adjustable combined frequency (Cascaded Sum Frequen-cy Generation, SFG). 2. The femtosecond non-collinear optical parameter amplifier according to item 1 of the patent application range, wherein the wavelength of the incident light is about 800 nm near-infrared light. 3. The femtosecond non-collinear optical parameter amplifier according to item 1 of the patent application scope, wherein the wavelength of the frequency-doubled light is about 40 Onm blue light. 4 · The femtosecond non-collinear optical parameter amplifier according to item 1 of the patent application range, wherein the thickness of the BB0 crystal for frequency doubling is 100 to 300 microns thick Page 17 1239128 6. Scope of patent application 5. The femtosecond non-collinear optical parameter amplifier according to item 1 of the patent scope 'where the thickness of the Ca window (win (jow) is 1 to 3 mm thick. Hour 6 · For example, the femtosecond non-collinear optical parameter amplifier of the scope of patent application, in which the tunable combined frequency is a blue light source with a wavelength of 38 0 to 65nm. The femtosecond non-collinear mode of scope of the patent application Optical parameter magnification 'wherein the angle between the seed light and the excitation light source is _8.4 degrees to 14 degrees.