Conical lens, UV fused silica, installed

A conical lens, also known as a rotationally symmetric prism, is a lens composed of a conical surface and a plane. Cone lenses are commonly used to generate Bessel intensity distribution beams or conical non diverging beams. When transforming a collimated beam into a circular beam, the plane of the conical lens should face the collimated light source.

Conical lens, UV fused silica, installed

Overview

feature

• Installed Ø 1/2 inch and Ø 1 inch UV fused silica cone lens

• Bottom angles provided: 0.5 °, 1.0 °, 2.0 °, 5.0 °, 10.0 °, 20.0 °, and 40.0 °

• Provide versions without coating or coated with broadband anti reflective film

￮ 350 - 700 nm(-A膜)

￮ 650 - 1050 nm(-B 膜)

￮ 1050 - 1700 nm(-C 膜)

• compatibleComponents of SM thread

• Also providedUnmounted ultraviolet fused silica cone lens

application

• laser drilling

• Optical Capture

• Optical coherence tomography (OCT)

A conical lens, also known as a rotationally symmetric prism, is a lens composed of a conical surface and a plane. Cone lenses are commonly used to generate Bessel intensity distribution beams or conical non diverging beams. When transforming a collimated beam into a circular beam, the plane of the conical lens should face the collimated light source.

Thorlabs' installed ultraviolet fused silica (UVFS) cone lens includes Ø 1/2 inch and Ø 1 inch versions, with SM05 (0.535 '-40) and SM1 (1.035' -40) thread housings, respectively, for compatibility with our SM thread series components. The base angle range of these conical lenses is from 0.5 ° to 40 °. They are made of high-quality ultraviolet fused silica, which is very suitable for high-power laser applications. The shell is engraved with wireless symbols and arrows pointing in the direction of wireless conjugation.

The installed conical lenses come in three versions with either uncoated or double-sided coated broadband anti reflective films: - A (350-700 nm), - B (650-1050 nm), or - C (1050-1700 nm). Both sides are coated with anti reflective film engraved to reduce surface reflection, thereby improving transmittance (R(avg) < 0.5%)。 If you need customized coating, please contact technical support.

When a conical lens refracts light, it follows Snell's law. Can be used to measure deflection angle:

among which,nIt is the refractive index of glass,alphaIt is the physical base angle of a conical lens,ßIt is the deviation angle between refracted light and the optical axis. Assuming the refractive index of air is 1 here. Please refer to Figure 1.1 for details.

General Specifications

beam shape

The beam generated by a conical lens

• Bessel beam: No diffraction

• Circular beam: very suitable for laser drilling

Figure 2.1:The absolute value of a Bessel function of order 0 (th). A true Bessel beam requires each ring to have the same energy as the central peak, therefore it requires noX quantityThe energy.

Figure 2.2:Cone lens ray diagram.

Bessel beam is a non diffracting concentric ring beam, and each concentric ring has the same power as the central ring. Technically speaking, it is impossible to generate Bessel beams because it requires noX quantityThe energy. But by passing a Gaussian beam through a conical lens and making the projection of the beam close to the conical surface of the lens, a beam very similar to the Bessel distribution can be generated. Figure 2.1 shows the absolute value of this 0 (th) order Bessel function.

When the beam is projected away from the lens, a single annular beam is formed. In fact, the beam is conical (i.e. the diameter increases with distance), but the light does not diverge, so the thickness of the ring remains unchanged (see Figure 2.2). The thickness of the ring is half the diameter of the incident laser beam. This type of beam is commonly used in laser drilling applications.

rounded corner

The intensity distribution of the generated Bessel beam and annular Gaussian beam will be affected by the top defect. If the top is circular, the central lobe of a zero order Bessel beam will exhibit intensity oscillations rather than spatial consistency (1), while a hollow Gaussian beam has an asymmetric ring with the tail facing towards the center or secondary ring (2). in order tobetterThorlabs manufactures conical lenses internally to reduce rounded cornersW AllControl the production process to ensure that the minimum diameter of the rounded corners is only 0.70 mm.

Figure 2.3:Experimental setup for generating hollow annular Gaussian beams.

Figure 2.4:As shown on the observation screen, the circular beam generated by Thorlabs' conical lens (a) and two general conical lenses [(b) and (c)]. The ring generated by Thorlabs cone lenses transitions from high intensity to low intensity in a short range, while general cone lenses transition on more pixels. The white horizontal line represents the location of the intensity distribution extracted in Figure 2.5.

Since any defects at the top of the conical lens can affect the properties of the emitted light beam, we demonstrate the quality of the Thorlabs conical lens by comparing the hollow Gaussian beams produced by the Thorlabs conical lens with two general conical lenses. The annular beam is generated using the experimental setup shown in Figure 2.3, which includes a 633 nm laser, GBE05-A 5X achromatic Galileo beam expander, SM2D25D SM2 ring driven variable aperture, conical lens (AX2520 and two general conical lenses with a cone angle of 20 °), and EDU-VS1 polystyrene observation screen. in order to obtainbetterPerformance: The laser incident on the conical lens must be a collimated small diameter beam. This can be achieved by first expanding the collimated beam, and then passing the beam through a 2.0 mm aperture. Then project the obtained beam shape onto the observation screen. The observation screen is located in the far-field position. For ease of movement, the observation screen is installed on a dovetail guide with a snap in slider.

Figure 2.4 shows the circular Gaussian beams generated by three types of test cone lenses displayed on the observation screen. In terms of beam quality, the Thorlabs conical lens (Figure 2.4 (a)) generates a clean circular beam with high contrast between the edges of the ring and the dark center. However, the quality of the circular beam generated by the conical lens of other manufacturers varies. As shown in Figure 2.4 (c), one of the rings generated by a general conical lens has poor contrast between high-intensity and low-intensity regions. The main ring appears weak, and a non-zero intensity distribution is visible within the ring. The second type of conical lens in the bottom image generates a clean ring, but the contrast between the edge of the ring and the dark center is noticeably weaker.

In order to highlight the intensity changes of the obtained beam, pseudo color scaled versions of these images were made and line contours were extracted. Figure 2.4 shows the original image (left) and the pseudo color image (right) side by side; A white line in the figure indicates the location of the intensity distribution map, and Figure 2.5 displays the corresponding pixel information. The comparison of the line intensity of the three tested conical lenses shows that Thorlabs' conical lens has the most distinct intensity peak, that isbetterContrast, because its intensity changes from bright to dark at the minimum number of pixels. And generally, conical lenses transition from bright edges to zero intensity centers over a larger pixel range, which can be seen at the tail where the asymmetric intensity peak slowly decays. This situation will result in a decrease in contrast between the bright ring and the hollow. Please note that the non-zero peak at the center of the ring is the expected effect, as only the idealbetterThe conical lens has high-intensity edges and zero intensity elsewhere. By improving the fillet diameter and reducing surface defects of the conical lens, the contrast between high-intensity areas and non-zero centers can be enhanced.

Figure 2.5:The line contour extracted from the circular beam image in Figure 2.4. Thorlabs' conical lens has the most distinct intensity peak, with the steepest transition from the bright edge to the zero intensity center. Intensity is expressed in arbitrary units and is not an absolute measurement. The position is also provided in arbitrary units, but it depends on the number of pixels.

damage threshold

Damage threshold of ultraviolet fused silica cone lens

Table 3.1 is the measurement data of Thorlabs ultraviolet fused silica lens. The damage threshold specification is fixed for all UV fused silica lenses, regardless of the size of the lens.

Table 3.1 Damage Threshold Specifications

annotation

a. The power density of the beam should be calculated in units of W/cm. Why is linear power density associated with long pulses and continuous lightbetterMeasurement, please refer to the "Continuous Wave and Long Pulse Laser" section below.

b. The specified damage threshold is an authentication measurement, rather than the actual damage threshold (i.e. the maximum output that optical components can withstand in a undamaged state).

Laser induced damage threshold tutorial

The following briefly introduces how to measure laser-induced damage threshold and how to determine whether optical components are suitable for specific applications based on damage threshold specifications. It is important to understand the laser-induced damage threshold (LIDT) of optical components when selecting them. The LIDT of optical components largely depends on the type of laser you are using. Continuous wave (CW) lasers generally cause damage through thermal effects (absorption of film or substrate). Pulsed lasers typically strip electrons from the lattice structure of optical components before causing thermal damage. Please note that the guidelines provided here are based on room temperature operation and brand new optical components (i.e., compliance with scratch spot specifications, no surface contamination, etc.). Due to the fact that dust or other particles on the surface of optical components can lower the damage threshold, we recommend keeping the surface of optical components clean and free from impurity contamination. For more information on cleaning optical components, please refer to our optical component cleaning tutorial.

test method

Thorlabs tests LIDT according to ISO/DIS 11254 and ISO 21254 standards.

Firstly, we will incident a low-power/energy beam onto the optical component under test. The 10 positions of the optical component are exposed to this laser beam for 30 seconds (continuous laser) or several pulses (specified pulse repetition rate). After exposure, use a microscope (magnification~100X) to detect the presence of visible damage. Record the number of damaged locations and their corresponding power/energy. Next, increase or decrease the power/energy of the incident light and expose it at 10 new positions on the optical component. Repeat the above process until damage is observed. In this way, the damage threshold is the highest power/energy that an optical component can withstand without damage. Figure 37B shows the test results of a BB1-E02 reflector.

According to the test results, the damage threshold of the reflector is 2.00 J/cm2 (532 nm, pulse width 10 ns, 10 Hz, Ø 0.803 mm). Please note that these tests were conducted on clean optical components as impurities and contaminants may significantly reduce the component damage threshold. This test result only represents a certain type of membrane layer, and the damage threshold specification of Thorlabs may vary depending on the membrane layer.

Continuous wave and long pulse lasers

When optical components are damaged by continuous wave (CW) laser, it is usually due to the absorption of laser energy causing surface melting or damage to the optical film layer (anti reflective film). When analyzing LIDT, pulses with a pulse width greater than 1 µ s can be considered as continuous lasers.

Table 37C Test Data Example

When the pulse width is between 1 ns and 1 µ s, laser-induced damage may occur due to absorption or dielectric breakdown, so users must analyze both continuous wave and pulse LIDT simultaneously. Absorption may be caused by inherent properties or surface irregularities of optical components; LIDT values are only valid for optical components that meet or exceed the surface quality specifications provided by the manufacturer. Although many optical components can withstand high-power continuous wave lasers, the continuous wave damage threshold of optical components such as bonded (such as achromatic dual lens) or high absorption (such as neutral density filter) is lower because the absorption or scattering of the bonding layer or metal film can reduce the damage threshold.

High pulse repetition frequency (PRF) pulsed lasers are similar to continuous beams. However, this largely depends on factors such as absorption and thermal diffusion, so there is no reliable method to determine whether high PRF lasers will damage optical components due to thermal effects. For high PRF beams, their average power and peak power must be compared to the same CW power. In addition, for highly transparent materials, when PRF increases, LIDT is almost non-existentW AllNo decrease.

In order to use the specified continuous wave damage threshold for optical components, it is necessary to understand the following information:

1. Your laser wavelength

2. Beam diameter (1/e (2))

3. Approximate intensity profile of a beam (such as Gaussian distribution)

4. Linear power density of the beam (total power divided by 1/e (2) beam diameter)

Thorlabs uses W/cm to express the LIDT value of CW laser. In this way, LIDT given by linear power density can be used for any beam diameter; No need to recalculate due to changes in spot size, as shown in Figure 37D. Calculate the average linear power density using the following formula.

The above calculation formula assumes a uniform beam intensity profile. Now, you must consider hotspots or other non-uniform intensity profiles in the beam and roughly calculate the maximum power density. For example, the maximum power density of Gaussian light is usually twice that of a uniform beam (as shown in Figure 37E).

Now, compare the maximum power density with the LIDT specified for optical components. If the testing wavelength of the optical component is not equal to your working wavelength, the damage threshold must be appropriately scaled. Based on experience, there is a linear relationship between damage threshold and wavelength. So, as the wavelength decreases, the damage threshold also decreases (for example, the damage threshold of LIDT at 1310 nm is 10 W/cm, and at 655 nm it decreases to 5 W/cm):

This rule of thumb only provides general trends and is not a quantitative analysis of LIDT and wavelength. For example, for continuous light applications, the damage threshold is well proportional to the absorption of the film layer and substrate, which may not necessarily be proportional to the wavelength. Although the above process is a good empirical rule for LIDT calculation, if the working wavelength is different from the LIDT wavelength, please contact technical support. If the actual power density is less than the adjusted damage threshold, then the optical component should be suitable for your application.

Please note that there is a certain margin of error between the damage threshold we calibrated online and our test results, which can accommodate the differences between different batches of products. If necessary, we can provide separate testing information and testing certificates. We will use similar optical components for damage analysis (without damaging the customer's optical components). Testing may require additional fees or delivery time. Please contact technical support for more information.

pulsed laser

As mentioned above, pulsed lasers generally introduce different types of damage to optical components compared to continuous wave lasers. Pulsed lasers typically do not cause damage to optical components through thermal effects; But it causes damage to the material by generating a strong electric field that can induce dielectric breakdown in the material. Unfortunately, it is very difficult to compare the LIDT specifications of optical components with the laser you are using. There are multiple mechanisms by which pulsed lasers damage optical components, and the degree of damage depends on the laser pulse width. The highlighted section in Table 37F summarizes the pulse width corresponding to our specified LIDT values.

Pulses less than 10 (-9) seconds lack reliability when compared to our specified LIDT values. In this ultra short pulse range, various mechanisms dominate the damage mechanism [2], such as multiphoton avalanche ionization. On the contrary, the damage to optical components caused by pulses between 10 (-7) s and 10 (-4) s is due to dielectric breakdown or thermal effects. This means that the damage threshold of both continuous and pulsed lasers must be compared with the laser beam to determine whether the optical component is suitable for your application.

Table 37F Laser Induced Damage Interval

When comparing the LIDT given under a specific pulse laser with the laser you are using, the following information needs to be understood:

1. Your laser wavelength

2. Your beam energy density (total energy divided by 1/e (2) area)

3. Your laser pulse width

4. Your laser pulse repetition frequency (PRF)

5. The beam diameter of your laser (1/e (2))

6. The approximate intensity distribution of a beam (such as Gaussian distribution)

Your beam energy density needs to be calculated in J/cm (2). Figure 37G illustrates why the energy density of LIDT is expressed by short pulse light sourcesbettermeasurement. Under these conditions, the LIDT given by energy density is independent of the spot size; Therefore, there is no need to readjust the LIDT value due to changes in spot size. The calculation process assumes that the light intensity distribution is uniform. You must adjust the energy density to deal with hotspots or other non-uniform intensity distributions in the beam, and roughly calculate the maximum energy density. For example, the maximum energy density of Gaussian light is usually twice that of a 1/e (2) beam.

Now compare the maximum energy density with the LIDT given by the optical component. If the testing wavelength of the optical component is not equal to your working wavelength, the damage threshold must be appropriately scaled [3]. According to experience, the damage threshold is proportional to the square root of the wavelength ratio. So, as the wavelength decreases, the damage threshold also decreases (for example, the damage threshold at 1064 nm is 1 J/m (2), and at 532 nm it decreases to 0.7 J/cm (2)):

The beam diameter is also important when comparing damage thresholds. Although LIDT is not related to spot size when expressed in J/cm ²; However, a large beam of light may illuminate more defects, which may lead to greater changes in the laser damage threshold [4]. For the data here, use a beam smaller than 1 mm to measure LIDT. When the beam size is greater than 5 mm, LIDT (J/cm2) will also be related to the beam diameter, as larger beams tend to expose more defects.

Now, it is necessary to compensate for the pulse width. The longer the pulse width, the more energy the optical component can withstand. For pulse widths ranging from 1 ns to 100 ns, the relationship can be approximated as:

This formula can be used to calculate and adjust LIDT based on your pulse width. If the maximum energy density of the laser used is less than the adjusted LIDT maximum energy density, the optical component is suitable for your application. Please note that this calculation only applies to pulsed lasers between 10 (-9) s and 10 (-7) s. For pulsed lasers between 10 (-7) s and 10 (-4) s, you also need to investigate whether they meet the requirements of continuous wave LIDT.

Please note that there is a certain margin of error between the damage threshold we calibrated online and our test results, which can accommodate the differences between different batches of products. If necessary, we can provide separate testing information and testing certificates. Please contact technical support for more information.

Laser induced damage threshold (LIDT) calculation

To introduce how to determine whether a given laser system damages optical components, many calculation examples of laser-induced damage threshold (LIDT) are given below. For the convenience of similar calculations, we provide a spreadsheet calculator that can be downloaded by clicking the button on the right. When using a calculator, first enter the LIDT value specified for the optical component and the relevant parameters of your laser system in the green box. The spreadsheet will calculate the linear power density of CW and pulse systems, as well as the energy density values of pulse systems. Use these values according tocognitionThe scaling method is to calculate the LIDT value of the optical component that has been adjusted and scaled proportionally. The calculator assumes a Gaussian beam profile, therefore correction factors (such as uniformity) must be introduced for other beam shapes. LIDT scaling is determined based on experience; Accuracy cannot be guaranteed. Note that in certain spectral regions, the absorption ability of optical elements or film layers towards laser may significantly reduce LIDT. These LIDT values are invalid for ultra short pulses with a pulse width less than 1 ns.

Figure 71A:The maximum light * of a Gaussian beam distribution is approximately twice that of a uniform beam distribution.

CW laser example

Assuming a CW laser system outputs a 0.5 W Gaussian beam with a diameter of 10 mm and 1/e (2) at 1319 nm. The average linear power density of the beam is obtained by directly dividing the total power by the beam diameter, which is 0.5 W/cm

However, the maximum power density of Gaussian beams is approximately twice that of uniform beams, as shown in Figure 71A. Therefore, the more accurate maximum linear power density of the system is 1 W/cm.

The CW LIDT specified for AC127-030-C achromatic dual lens is 350 W/cm, measured at 1550 nm. The CW damage threshold is usually directly proportional to the wavelength of the laser source, resulting in an adjusted LIDT value:

The adjusted LIDT value of 350 W/cm x (1319 nm/1550 nm)=298 W/cm is significantly higher than the maximum linear power density of the laser system, therefore the use of this dual lens in the system is safe.

Example of pulsed nanosecond laser: scaling with different pulse widths

Assuming a pulsed Nd: YAG laser system with a third harmonic output of 355 nm, 10 Hz, a pulse width of 2 ns, a single pulse energy of 1 J, and a Gaussian beam diameter of 1.9 cm (1/e (2)). The average energy density of each pulse is obtained by dividing the pulse energy by the beam area

As mentioned above, the maximum energy density of Gaussian beams is approximately twice the average energy density. Therefore, the maximum energy density of the beam is~0.7 J/cm (2).

Compare the energy density of this beam with the LIDT value of 1 J/cm (2) specified for BB1-E01 broadband dielectric film reflector and the LIDT value of 3.5 J/cm (2) specified for NB1-K08 Nd: YAG laser line reflector. Both LIDT values were measured at 355 nm using a pulsed laser with a pulse width of 10 ns and a repetition rate of 10 Hz. Therefore, it is necessary to adjust the shorter pulse width of the system. As described in the previous label, the LIDT value of nanosecond pulses is proportional to the square root of the laser pulse width:

Using this adjustment factor, the LIDT value of BB1-E01 broadband mirror becomes 0.45 J/cm (2), and the LIDT value of Nd: YAG laser line mirror becomes 1.6 J/cm (2), which are directly compared with the maximum energy density of the beam of 0.7 J/cm (2). Broadband mirrors are likely to be damaged by laser, but special laser line mirrors can be used in laser systems.

Example of pulsed nanosecond laser: scaling at different wavelengths

Assuming a pulsed laser system emits 10 ns pulses at 2.5 Hz, with each pulse having an energy of 100 mJ at 1064 nm and a 1/e (2) beam diameter of 16 mm, we now need to use a neutral density filter for attenuation. For Gaussian output, use these specifications to calculate a maximum energy density of 0.1 J/cm (2).

For a 10 ns pulse at 355 nm, the damage threshold of a reflective neutral density filter with NDUV10A Ø 25 mm and OD 1.0 is 0.05 J/cm (2), while for a 10 ns pulse at 532 nm, the damage threshold of a similar NE10A absorption filter is 10 J/cm (2). According to the description in the previous label, for nanosecond pulses, the LIDT value of the optical element is proportional to the square root of the wavelength:

According to this ratio, the adjusted LIDT value for reflective filters is 0.08 J/cm (2), and for absorptive filters it is 14 J/cm (2). In this case, to prevent optical damage, the absorption filter isbetterchoice.

Example of Pulse Microsecond Laser

Consider a laser system that generates 1 µ s pulses, with a single pulse energy of 150 µ J and a repetition rate of 50 kHz, which will result in a relatively high duty cycle of 5%. The system is located between CW and pulsed laser-induced damage, which may cause damage to optical components through any mechanism. Therefore, both CW and pulse LIDT values must be compared with the properties of the laser system to ensure safe operation.

If this longer pulse laser emits a Gaussian beam with a diameter of 12.7 mm and a wavelength of 980 nm, the linear power density of the laser output is 5.9 W/cm, and the single pulse energy density is 1.2 x 10 (-4) J/cm (2). Compare this value with the LIDT value of WPQ10E-980 polymer zero order quarter wave plate, which is 5 W/cm for 810 nm continuous wave and 5 J/cm for 10 ns pulse at 810 nm (2). As before, the CW LIDT of the optical component is linearly proportional to the laser wavelength, so the adjusted CW value at 980 nm is 6 W/cm. On the other hand, the pulse LIDT is proportional to the square root of the laser wavelength and the square root of the pulse width, so the adjusted value for a 1 µ s pulse at 980 nm is 55 J/cm (2). The pulse LIDT of optical components is significantly higher than the energy density of laser pulses, so a single pulse will not damage the waveplate. However, the average linear power density of laser systems is relatively high, similar to high-power CW beams, which may cause thermal damage to optical components.

Product ordering information

Installed conical lens, uncoated

These conical lenses are uncoated and used in the wavelength range of 185 nm to 2.1 µ m. Their substrate is ultraviolet fused silica, which is very suitable for applications from ultraviolet to near-infrared. Compared with N-BK7, UV fused silica has better uniformity and lower thermal expansion coefficient.

The optical components below are fixed in the housing through SM snap rings. Caution must be taken when removing optical components from the mounting bracket to prevent damage to the optical components.

a. The deflection angle is calculated using light at 532 nm.

b. Typical transmittance curve of a 10mm thick window panel.

General (14 items)

Installed conical lens, anti reflective film: 350-700 nm

These conical lenses are coated with an anti reflective film for the wavelength range of 350-700 nm, making them ideal for some near ultraviolet (NUV) and all visible light bands. This wavelength range is very suitable for helium neon lasers and other visible light lasers.

The optical components below are fixed in the housing through SM snap rings. Caution must be taken when removing optical components from the mounting bracket to prevent damage to the optical components.

a. The deflection angle is calculated using light at 532 nm.

b. Every surface.

General (14 items)

Installed conical lens, anti reflective film: 650-1050 nm

The wavelength range of the anti reflective film of these conical lenses is from 650 to 1050 nm, which is very suitable for many near-infrared (NIR) applications such as optical capture and corneal surgery.

The optical components below are fixed in the housing through SM snap rings. Caution must be taken when removing optical components from the mounting bracket to prevent damage to the optical components.

a. The deflection angle is calculated from 850 nm light.

b. Every surface.

General (14 items)

Installed conical lens, anti reflective film: 1050-1700 nm

The anti reflective film range of these conical lenses is from 1050 to 1700 nm, making them highly suitable for near-infrared (NIR) applications. This wavelength range covers wavelengths for applications such as optical coherence tomography (OCT), optical capture, and laser drilling. The use of conical lenses in these applications can improve the focusing depth of the sample arm.

The optical components below are fixed in the housing through SM snap rings. Caution must be taken when removing optical components from the mounting bracket to prevent damage to the optical components.

a. The deflection angle is calculated from 1310 nm light.

b. Every surface.

General (14 items)